A sodium electric layer oxide positive electrode of hetero-coherent double superlattice and a preparation method thereof

Abstract

The application discloses a sodium electric layer-like oxide positive electrode of heterogeneous coherent double superlattice and a preparation method. x Li 1‑x ]Li y Ni m Fe z Mn 2m O2, which is an O3 type positive electrode material, 0.9<=x<=0.97, 0.04<=y<=0.06, 0.04<=z<=0.06, m=0.3, y+z+3m=1, 0.08<=1-x+y<=0.15. The material is prepared by a solid phase sintering method, the element distribution is uniform, and the structure simultaneously exists in two kinds of superlattices of a fence type and a honeycomb type. By precisely controlling the nickel and manganese ratio and introducing lithium and iron, the formation of the fence type and the honeycomb type heterogeneous coherent double superlattice structure is successfully induced. The structure can not only activate the reversible oxidation and reduction reactions of anions and cations to improve the specific capacity, but also effectively inhibit the transition metal migration and oxygen release in the cycle process. The lithium in the sodium layer enhances the structural stability by forming LiO6 columnar units, the double superlattice effectively inhibits the transition metal migration, reduces the oxygen release and provides a sodium ion transmission channel, so that the oxidation and reduction reversibility and the structural durability of the material are significantly improved. The positive electrode material has high reversible specific capacity, high energy density and long cycle life at a high working voltage, and is especially suitable for the requirements of long service life, high safety and low cost of sodium ion batteries in the large-scale energy storage field.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion battery layered oxide cathode with heterogeneous coherent double superlattice and its preparation method. Background Technology

[0002] Currently, lithium-ion batteries, widely used in grid-scale energy storage systems, are facing severe challenges, primarily due to the limited global lithium resources and their highly uneven geographical distribution. With the rapid development of the electric vehicle industry, the demand for lithium resources continues to rise, further intensifying resource competition and gradually diminishing the cost advantage of lithium-ion batteries in large-scale energy storage applications. Against this backdrop, sodium-ion batteries, with their abundant resources and economic advantages, have emerged as a promising alternative energy storage technology. Sodium is abundant and evenly distributed in the Earth's crust, and its raw material cost is significantly lower than that of lithium. Furthermore, sodium-ion batteries operate on a similar principle to lithium-ion batteries and can be produced within the existing lithium battery industry chain, possessing a significant industrialization foundation. These characteristics make sodium-ion batteries particularly suitable for grid-scale energy storage applications that are cost-sensitive but have relatively low energy density requirements.

[0003] Among sodium-ion battery cathode materials, manganese-based layered oxide materials have attracted widespread attention due to their high theoretical specific capacity, suitable operating voltage, abundant resource reserves, environmental friendliness, and relatively simple synthesis process, demonstrating a good cost advantage. However, such materials still face severe challenges in practical applications: (1) Their capacity below 4V mainly depends on the limited redox reaction of transition metals (TM), resulting in a low theoretical capacity. If the upper limit cutoff voltage is increased to above 4V, a higher capacity can be achieved, but the mechanical stability problem becomes more significant, leading to a further decline in cycle performance. (2) Irreversible phase transitions and lattice distortions easily occur during sodium ion insertion / extraction, resulting in poor cycle stability. (3) Transition metal elements such as Mn are prone to dissolution and migration, damaging the material structure and accelerating performance degradation.

[0004] Studies have shown that introducing Li, which has extremely low electronegativity, can... + It is one of the effective means. When Li + When occupying the TM layer, the strong ionic bonds formed between Li and oxygen can modulate the O 2p band structure, inducing a reversible oxygen anion redox reaction, thereby further increasing the capacity; simultaneously, Li + With Mn 4+ The difference in plasma radius contributes to the formation of locally ordered superlattice structures, enhancing the stability of the crystal framework. Furthermore, due to the Ni... 2+ With Li + Having similar ionic radii, therefore, theoretically speaking, when Ni 2+ and Mn 4+A molar ratio of 1:2 between the two elements will form a honeycomb superstructure. Furthermore, introducing Fe with a larger radius into manganese-based materials increases the TM-O bond length and reduces the band gap between the O band and the conduction band. This facilitates better electron gain and loss for lattice oxygen, and the ligand charge transfer effect of Fe 3d-O2p can also optimize oxygen reactions, enhancing the material's kinetic properties. However, existing modification studies are mostly limited to single-element doping or simple co-doping, making it difficult to achieve synergistic improvements in multiple properties. For example, Li-activated anionic redox reactions lead to irreversible oxygen release, and the introduction of excessive Ni or Fe may exacerbate structural degradation during cycling. Therefore, how to construct a composite superlattice structure that can simultaneously stabilize anionic and cation redox reactions in materials through precise multi-element site control remains a pressing technical challenge in this field.

[0005] Based on the above analysis, this invention aims to provide a novel layered oxide cathode material for sodium-ion batteries and its preparation method. By precisely designing the Ni / Mn molar ratio to induce the formation of a honeycomb superlattice framework, and synergistically introducing trace amounts of Li at Na and TM sites to construct a LiO6 prism stabilizer and a fence-type superlattice, while simultaneously introducing an appropriate amount of Fe to activate anion redox, an O3 cathode material with a heterogeneous coherent dual superlattice structure is finally prepared. This material can simultaneously activate and stabilize cation redox below 4V and anion redox above 4V, improving Na… + The diffusion rate is reduced, inhibiting the migration of transition metals, thus exhibiting excellent rate performance and structural stability. Furthermore, this cathode material demonstrates good electrochemical performance in full-cell testing, showing promising prospects for large-scale production. Summary of the Invention

[0006] The present invention aims to provide a sodium-ion layered oxide cathode material with a heterogeneous coherent double superlattice structure, which can be prepared by a simple high-temperature solid-state method and is suitable for large-scale energy storage devices.

[0007] Another objective of this invention is to propose a heterogeneous coherent double superlattice structure formed by element substitution.

[0008] This invention is achieved using the following technical solution:

[0009] Sodium, lithium, nickel, iron and manganese sources are mechanically ground and mixed to obtain a homogeneous mixture, which is then calcined in an air or oxygen atmosphere. After cooling, a cathode material with a heterogeneous coherent double superlattice structure is obtained.

[0010] Preferably, the molar ratio of sodium, lithium, nickel, iron and manganese is: Na : Li : Ni : Fe : Mn = (0.9~0.97): (0.08~0.15) : 0.3 : (0.04~0.06) : 0.6, and the content of each element can be arbitrarily adjusted within the above range.

[0011] Preferably, the sodium salt is selected from one or more of sodium carbonate, sodium nitrate, or sodium acetate.

[0012] Preferably, the manganese salt is selected from one or more of manganese carbonate, manganese acetate, or manganese trioxide.

[0013] Preferably, the calcination process is set at 800–1050°C for 10–15 hours, and the heating rate is controlled at 2–10°C / min.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The heterogeneous coherent double superlattice sodium-ion layered oxide cathode material provided by this invention can be prepared using a traditional solid-state reaction method. Specifically, it involves grinding and mixing sodium salt, lithium salt, and oxides of nickel, iron, and manganese, followed by one-step calcination to obtain the target product. This method has a simple process flow, requires no complex operations, and produces no pollutants or harmful gases during preparation, meeting the requirements of green and clean production and possessing good prospects for large-scale application.

[0016] Through precise elemental design, this invention successfully constructed two heterogeneous superlattice structures: a honeycomb NiMn6 superlattice that activates anion redox reactions, thereby enhancing the material's capacity; and a fence-type superlattice whose ultra-wide spacing facilitates sodium ion transport, thus stabilizing the crystal structure. Furthermore, lithium ions further activate cation redox activity by modulating local electron orbitals, resulting in excellent rate performance and cycle stability. The combined effect of these composite superlattices effectively suppresses transition metal layer slip and lattice mismatch, alleviating structural stress and enabling the material to exhibit both high structural stability and high specific capacity within the 1.5–4.5 V voltage range.

[0017] Therefore, the cathode material prepared by this invention exhibits high discharge capacity, high energy density and good cycle stability in half-cell tests. In addition, its preparation process is simple and easy to scale up, making it particularly suitable for large-scale energy storage applications of sodium-ion batteries. Attached Figure Description

[0018] Figure 1 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05Mn 0.6 X-ray diffraction (XRD) pattern of O2 material.

[0019] Figure 2 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 Schematic diagram of the structure of O2 material.

[0020] Figure 3 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 Scanning electron microscope (SEM) image of O2 material.

[0021] Figure 4 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 Transmission electron microscopy (TEM) EDS energy dispersive spectroscopy of O2 materials.

[0022] Figure 5 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 The first charge-discharge curve of O2 material assembled into a button cell at a 0.1C rate within a voltage range of 1.5-4.5V.

[0023] Figure 6 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 The first-cycle dQ / dV curve of O2 material assembled into a button cell at a 0.1C rate within a voltage range of 1.5-4.5V.

[0024] Figure 7 This is a comparison chart showing the rate performance of Example 1 and Comparative Example 1 as button cells assembled using sodium-ion battery cathode materials in the voltage range of 1.5-4.5V.

[0025] Figure 8This is a comparison of the electrochemical performance of Example 1 and Comparative Example 1, which were assembled into coin cells using sodium-ion battery cathode materials, after 100 cycles at a 0.5C rate within a voltage range of 1.5-4.5V.

[0026] Figure 9 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 The first two charge-discharge curves of a full cell assembled with O2 material and hard carbon anode at a current density of 0.1C.

[0027] Figure 10 Example 1 [Na] 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2 material is matched and assembled with hard carbon anode to achieve a full cell cycle performance of 100 cycles. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments.

[0029] The experimental methods mentioned in the following embodiments and comparative examples are all conventional methods. The embodiments of the present invention can obtain the same results through different implementation methods. Those skilled in the art can make appropriate modifications without violating the experimental results. Therefore, the present invention is not limited to the specific implementation of the following content.

[0030] Unless otherwise specified, the reagents and materials described in the following examples are commercially available.

[0031] Example 1

[0032] The following describes the preparation of a heterogeneous coherent double superlattice sodium-ion layered oxide cathode material. The chemical formula of the material in this embodiment is [Na 0.95 Li 0.05 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2.

[0033] The following describes the preparation process of sodium-ion layered oxide cathode material with heterogeneous coherent double superlattice:

[0034] At room temperature, powders were weighed according to a molar ratio of sodium carbonate:lithium carbonate:nickel oxide:ferric oxide:manganese oxide of 9.5:1:3:0.5:6. The powders were then thoroughly ground in a natural agate mortar for 45 minutes. Subsequently, the powders were pressed into cylindrical sheets approximately 3 mm thick using a 10 mm diameter mold. These sheets were placed in a muffle furnace and sintered in air at a heating rate of 5 °C / min to 1050 °C for 10 h. After natural cooling to approximately 100 °C, the powdered cathode material was obtained.

[0035] The following describes the preparation process of a sodium-ion layered oxide cathode with a heterogeneous coherent double superlattice:

[0036] The prepared positive electrode material, polyvinylidene fluoride (PVDF), and conductive agent were mixed at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added dropwise, and the mixture was shaken for 20 min to prepare a uniform slurry. The slurry was then coated onto an Al foil current collector and transferred to a vacuum drying oven, heated to 80°C, and held for 12 h. Finally, it was cut into circular electrode sheets with a diameter of 10 mm using a manual cutting machine and properly stored for later use.

[0037] The positive electrode sheet prepared above was used in the preparation of a sodium-ion half-cell. The preparation process is as follows:

[0038] The electrolyte used was 1 mol / L NaClO4 solvent (a 1:1 volume ratio mixture of ethylene carbonate EC and dimethyl carbonate DEC). The separator (glass fiber filter paper separator, Whatman GF / D, battery grade) was cut into 20 mm diameter discs. The coin cell assembly used a CR2032 coin cell casing, assembled in the following order: negative electrode shell, sodium plate, separator, positive electrode plate, gasket, spring clip, and positive electrode shell. The casing was then sealed using a sealing machine under 50 MPa pressure. Each coin cell used approximately 100 μL of electrolyte, which was applied equally to both sides of the separator to ensure complete wetting. The entire coin cell assembly process was completed in an argon-atmosphere glove box. In this invention, all electrochemical performance tests were performed at room temperature, with the battery test voltage range being 1.5–4.5 V.

[0039] The positive electrode sheet prepared above was used in the preparation of sodium-ion full cells. The preparation process is as follows:

[0040] The electrolyte is a self-prepared NaClO4 solvent mixture. The separator (glass fiber filter paper separator, Whatman GF / D, battery grade) is cut into 20 mm diameter discs. The coin cell assembly uses a CR2032 coin cell case, assembled in the following order: negative electrode shell, hard carbon negative electrode sheet, separator, positive electrode sheet, gasket, spring clip, and positive electrode shell. The cells are sealed using a sealing machine under 50 MPa pressure. Each coin cell uses approximately 100 μL of electrolyte, which is applied equally to both sides of the separator to ensure complete wetting. The entire coin cell assembly process is performed in an argon-atmosphere glove box. In this invention, all full-cell electrochemical performance tests are conducted at room temperature, with a voltage range of 1.5–4.5 V.

[0041] Material structure and electrochemical performance characterization:

[0042] The crystal structure of the cathode material in Example 1 was analyzed using powder X-ray diffraction, and the results are as follows: Figure 1 As shown in the XRD pattern, the material in Example 1 is an O3-type cathode material. Its X-ray diffraction pattern shows fence-type and honeycomb-type superlattice diffraction peaks at 2θ = 17.2° and 20°~21°, respectively. A schematic diagram of its structure is shown below. Figure 2 As shown. Scanning electron microscopy characterized the morphology of the product from Example 1, as shown. Figure 3 As shown, the material is distributed in a lamellar pattern. Figure 4 The energy dispersive spectroscopy of the transmission electron microscope showed that Na, Ni, Fe, Mn and O elements were uniformly distributed in the sample particles. Figure 5-7 This indicates the presence of significant Ni and O redox plateaus in the material of Example 1, which endow the material with high discharge capacity and good rate performance under high voltage. Meanwhile... Figure 8 This demonstrates that the material exhibits good cycling stability, retaining 79% of its capacity after 100 cycles at a current density of 0.5C. The rate capability and cycling results of the full cell assembled with the HC anode in Example 1 are as follows: Figure 9 , Figure 10 As shown, the initial coulombic efficiency can reach 80% in the voltage range of 1.5-4.15V, and the capacity retention rate reaches 68% after 100 cycles at 0.5C.

[0043] Example 2

[0044] The chemical formula of the material prepared in this embodiment is [Na]. 0.97 Li 0.03 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0045] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 9.7:0.8:3:0.5:6, and other preparation conditions were the same as in Example 1.

[0046] Example 3

[0047] The chemical formula of the material prepared in this embodiment is [Na]. 0.93 Li 0.07 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0048] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 9.3:1.2:3:0.5:6. Other preparation conditions were the same as in Example 1.

[0049] Example 4

[0050] The chemical formula of the material prepared in this embodiment is [Na]. 0.9 Li 0.1 Li 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0051] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 9:1.5:3:0.5:6, and other preparation conditions were the same as in Example 1.

[0052] Example 5

[0053] The chemical formula of the material prepared in this embodiment is [Na]. 0.95 Li 0.05 Li 0.06 Ni 0.3 Fe 0.04 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0054] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 9.5:1.1:3:0.4:6, and other preparation conditions were the same as in Example 1.

[0055] Example 6

[0056] The chemical formula of the material prepared in this embodiment is [Na]. 0.95 Li 0.05 Li0.04 Ni 0.3 Fe 0.06 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0057] At room temperature, powder was weighed according to the following ratio: sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide 9.5:0.9:3:0.6:6. Other preparation conditions were the same as in Example 1.

[0058] Comparative Example 1

[0059] The material prepared in this embodiment has the chemical formula NaFe. 0.1 Mn 0.9 O2, the specific preparation process is the same as in Example 1, the difference being:

[0060] At room temperature, the powder was weighed according to the molar ratio of sodium carbonate: ferric oxide: manganese oxide of 10:1:9, and other preparation conditions were the same as in Example 1.

[0061] Comparative Example 2

[0062] The material prepared in this embodiment has the chemical formula NaNi. 0.3 Mn 0.7 O2, the specific preparation process is the same as in Example 1, the difference being:

[0063] At room temperature, the powder was weighed according to the molar ratio of sodium carbonate: nickel oxide: manganese trioxide of 10:3:7, and other preparation conditions were the same as in Example 1.

[0064] Comparative Example 3

[0065] The material prepared in this embodiment has the chemical formula NaNi. 0.3 Fe 0.1 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0066] At room temperature, the powder was weighed according to the molar ratio of sodium carbonate: nickel oxide: ferric oxide: manganese oxide of 10:3:1:6, and other preparation conditions were the same as in Example 1.

[0067] Comparative Example 4

[0068] The material prepared in this embodiment has the chemical formula NaLi. 0.03 Ni 0.3 Fe 0.07 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0069] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 10:0.3:3:0.7:6, and other preparation conditions were the same as in Example 1.

[0070] Comparative Example 5

[0071] The material prepared in this embodiment has the chemical formula NaLi. 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0072] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 10:0.5:3:0.5:6, and other preparation conditions were the same as in Example 1.

[0073] Comparative Example 6

[0074] The material prepared in this embodiment has the chemical formula NaLi. 0.08 Ni 0.3 Fe 0.02 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0075] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: lithium carbonate: nickel oxide: ferric oxide: manganese oxide of 10:0.8:3:0.2:6, and other preparation conditions were the same as in Example 1.

[0076] Comparative Example 7

[0077] The chemical formula of the material prepared in this comparative example is NaMg. 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0078] At room temperature, powder was weighed according to the molar ratio of sodium carbonate: magnesium oxide: nickel oxide: ferric oxide: manganese oxide of 10:0.5:3:0.5:6, and other preparation conditions were the same as in Example 1.

[0079] Comparative Example 8

[0080] The chemical formula of the material prepared in this comparative example is Na□. 0.05 Ni 0.3 Fe 0.05 Mn 0.6 O2, the specific preparation process is the same as in Example 1, the difference being:

[0081] At room temperature, the powder was weighed according to the molar ratio of sodium carbonate: nickel oxide: ferric oxide: manganese oxide of 10:3:0.5:6, and other preparation conditions were the same as in Example 1.

[0082] Table 1 Electrochemical performance data of each example and comparative example

[0083]

Claims

1. A hetero-coherent bilayered sodium electroactive oxide cathode, characterized in that, The positive electrode material has both honeycomb type and fence type superlattice structures, and has a chemical formula of [Na x Li 1-x ]Li y Ni m Fe z Mn 2m O2, is an O3 type positive electrode material, 0.9≤x≤0.97, 0.04≤y≤0.06, 0.04≤z≤0.06, m=0.3, y+z+3m=1, 0.08≤1-x+y≤0.15; and the lithium element exists in the sodium layer and the transition metal layer simultaneously.

2. A method of preparing a sodium electro-layered oxide positive electrode of a hetero coherent bi-superlattice as claimed in claim 1, characterized in that, The method comprises the following steps: The sodium source, the lithium source, the nickel source, the iron source and the manganese source are fully ground to obtain a mixture, the molar ratio of sodium, lithium, nickel, iron and manganese is 0.9-0.97:0.03-0.15:0.3:0.04-0.06:0.6, the sodium is obtained from one of sodium carbonate, sodium nitrate and sodium acetate, the manganese is obtained from one of manganese carbonate, manganese acetate and manganese sesquioxide, the mixture is calcined and then cooled, the sintering atmosphere is air or oxygen atmosphere, the sintering equipment is a muffle furnace, the sintering temperature is 800-1050 DEG C, the temperature rising speed is 2-10 DEG C / min, and the positive electrode material with double superlattice structure is obtained.

3. A sodium-ion battery of inhomogeneous coherent bi-superlattice, characterized in that, The sodium battery layered oxide positive electrode with the heterogeneous coherent double superlattice structure comprises the positive electrode material with the double superlattice structure.

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