Manganese-based layered oxide with mixed structure as well as preparation method and application of manganese-based layered oxide

Abstract

The invention belongs to the technical field of sodium ion battery materials and electrochemistry, and provides a manganese-based layered oxide with an ordered and disordered mixed structure as well as a preparation method and application of the manganese-based layered oxide. The chemical formula of the oxide is NaxMyMnyO (x is larger than 0 and smaller than 1, y is larger than 0 and smaller than 1, and M is one or more of Mg, Fe, Al, Zn, Co, Ni, Cu and other elements), and the oxide belongs to a P2 phase and is composed of a specific ordered (-Mn-Mn-M-) and disordered (-Mn-Mn-Mn-) structure. The preparation method comprises the following steps: dissolving a sodium salt, an M salt, a manganese salt and an organic chelating agent in water according to a specific ratio to prepare a precursor mixed solution, heating, evaporating to dryness, grinding, and sintering. Compared with a traditional material, the oxide serving as a sodium-ion battery positive electrode active material can remarkably improve the capacity and reversibility of an oxidation-reduction reaction, inhibit voltage decline and enhance the stability of a crystal structure, is simple in synthesis process and low in cost, is expected to be applied to the fields of electric automobiles and large-scale energy storage, and relieves the mileage and price problems.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion battery materials and electrochemical technology, and specifically relates to a manganese-based layered oxide with a mixed structure, a preparation method and an application thereof. Background Art

[0002] Currently, lithium-ion batteries dominate the market for portable electronics and electric vehicles. However, due to the increasing demand for lithium and concerns about the high cost of lithium, researchers are developing battery energy storage technologies based on new chemistries. Sodium-ion batteries have attracted much attention due to their abundant resources, environmental friendliness, and low price. Among them, layered oxide cathodes are one of the most commercially promising cathode materials for sodium-ion batteries.

[0003] Traditional layered oxide cathodes mainly rely on cations (such as Ni 2+ ,Co 3+ ) The redox process provides charge compensation to drive the entire electrochemical reaction and contribute to the capacity. Recent studies have shown that the theoretical capacity and energy density of batteries can be effectively improved by utilizing the reversible redox reactions of anions, such as oxygen ions, rather than just cations. However, such compounds (such as Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Oxygen redox reactions such as the formation of oxygen vacancies, dimerization of OO (2O 2- →O2 n- ), O2 release, transition metal ion migration, phase change and cracking, which lead to poor cyclic stability, fast voltage decay and low safety of the material. In order to alleviate these problems, some solutions have been proposed, such as surface engineering and element doping to design and prepare positive electrode materials. However, these methods are often limited by factors such as complex synthesis steps, high cost and unclear mechanism. Therefore, it has become a scientific problem to design highly stable and reversible anionic reactive morphological oxides through simple synthesis methods. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a manganese-based layered oxide with an ordered and disordered mixed structure and its application in view of the shortcomings of the prior art. 2 / 3 M 1 / 3 Mn 2 / 3O2, through the simple adjustment of the chemical ratio of M / Mn, it forms two different structural configurations, one is an ordered structural configuration -M-Mn-M-; the other is a disordered structural configuration -Mn-Mn-Mn-. When used as a positive electrode active material for sodium ion batteries, it has extremely high specific capacity and extremely small voltage decay, and the stability and reversibility of the crystal structure and electrochemical reaction are greatly improved, effectively solving the above-mentioned problems faced by the anion reaction positive electrode. The manganese-based layered oxide of the ordered and disordered mixed structure of the present invention is used as a positive electrode material for sodium ion batteries, with a capacity of more than 200mAh g -1 The high capacity and stable cycle voltage of the cathode solve the dilemma of the anion reaction type cathode that cannot achieve both high capacity and stable voltage. Its simple synthesis process and low price are expected to be applied to electric vehicles and large-scale energy storage, alleviating mileage and price anxiety.

[0005] In order to achieve the above object, the present invention provides a manganese-based layered oxide with a mixed structure, characterized in that the manganese-based layered oxide has a chemical formula of Na 1-x M y Mn 1-y O2, 0<x<1, 0<y<1, belongs to the P2 phase, M is one or more of Mg, Fe, Al, Zn, Co, Ni, and Cu, and the mixed structure includes an ordered structure and a disordered structure, wherein in the ordered structure, two manganese atoms plus one M atom are arranged in the atomic form of -M-Mn-M- as the basic repeating unit; in the disordered structure, continuous manganese atoms -Mn-Mn-Mn- are arranged in the atomic form of the basic repeating unit. Furthermore, the average particle size of the manganese-based layered oxide is 1-2 μm, and the grain shape is plate-like.

[0006] The present invention also provides a method for preparing the manganese-based layered oxide having a mixed structure as described above, characterized in that it comprises the following steps: 1) Dissolve sodium salt, M salt, manganese salt and organic chelating agent in water and mix them evenly to obtain a precursor mixture; 2) heating the precursor mixture to dryness to obtain a precursor; 3) After the precursor is ground into powder, it is first pre-fired in air and then sintered in air or oxygen atmosphere to obtain a manganese-based layered oxide with an ordered and disordered mixed structure.

[0007] Furthermore, the sodium salt is one or more of anhydrous sodium nitrate, anhydrous sodium acetate, anhydrous sodium hydroxide, and sodium acetate trihydrate.

[0008] 5. The preparation method according to claim 3, characterized in that the M salt is one or more of anhydrous nitrate, anhydrous acetate, hexahydrate nitrate, and tetrahydrate acetate.

[0009] Furthermore, the manganese salt in step 1) is one or more of anhydrous manganese nitrate, anhydrous manganese acetate, manganese nitrate tetrahydrate, and manganese acetate tetrahydrate.

[0010] Furthermore, the organic chelating agent is one or more of citric acid and glycolic acid.

[0011] Furthermore, the molar ratio of the sodium salt, M salt, manganese salt, and organic chelating agent is (0.2-0.21): 0.05: 0.25: 0.3; and the volume of water is 0.1-1L.

[0012] Furthermore, the heating temperature in step 2) is 70-95°C; the pre-sintering temperature in step 3) is 400-550°C, and the pre-sintering time is 2-6h; when the sintering temperature is 750-900°C, the sintering time is 10-20h.

[0013] The present invention also provides an application of the manganese-based layered oxide with a mixed structure or the manganese-based layered oxide prepared by the above method as a positive electrode active material of a sodium ion battery.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention synthesizes for the first time a manganese-based layered oxide with a mixed structure of ordered and disordered structures, including two structural units, one is an ordered structural configuration -M-Mn-M-; the other is a disordered structural configuration -Mn-Mn-Mn-. The solid solution mixing of configurations with different oxygen activities in three-dimensional space is achieved, avoiding the excessive and regional concentration of oxygen-oxidation reactions. When used as a positive electrode active material for sodium ion batteries, it can significantly improve the capacity and reversibility of its redox reaction contribution. Compared with other positive electrode materials involving oxygen redox reactions, the redox reaction capacity of this material is high and the reversibility is good, the crystal structure is stable, and the voltage decay caused by the oxygen redox reaction is significantly suppressed.

[0015] 2) The modification process adopted in the present invention is simple and easy to implement. It only needs to simply adjust the chemical ratio of Mg / M to obtain a manganese-based layered oxide with a mixed structure of ordered and disordered structures, thus avoiding the cumbersomeness and uncertainty of post-processing processes such as foreign ion doping or surface coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work. In the drawings: Figure 1 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 XRD and refined patterns of O2.

[0017] Figure 2 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 SEM image of O2.

[0018] Figure 3 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 X-ray energy dispersion spectrum of O2.

[0019] Figure 4 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Comparison of charge and discharge curves of different cycles at O20.1C.

[0020] Figure 5 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Capacity comparison chart after 50 cycles at O20.1C.

[0021] Figure 6 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Comparison of discharge voltage after 200 cycles under O21C.

[0022] Figure 7 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Capacity comparison chart after 200 cycles under O21C.

[0023] Figure 8 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Comparison of high-angle annular dark-field images of O2 charged to 4.5V. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections.

[0026] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0027] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0028] In the embodiments shown in the drawings, the indications of directions (such as up, down, left, right, front and back) used to explain the structure and movement of the various components of the present invention are not absolute but relative. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, the indications of these directions also change accordingly.

[0029] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation of the present invention will be described below with reference to the accompanying drawings.

[0031] Example 1 A manganese-based layered oxide with an ordered and disordered mixed structure is prepared by the following steps: 1) Dissolve 0.2 mol of anhydrous sodium acetate, 0.05 mol of magnesium acetate tetrahydrate, 0.25 mol of manganese acetate tetrahydrate and 0.3 mol of citric acid in 0.3 L of water and mix well to obtain a precursor mixture; 2) heating the precursor mixture to 80°C and evaporating to dryness to obtain a precursor; 3) After the precursor was ground into powder, it was pre-sintered at 450 °C in air for 4 h, and then sintered at 850 °C in air for 18 h to obtain a manganese-based layered oxide Na with a mixed structure of ordered and disordered structures. 2 / 3 Mg 1 / 6 Mn 5 / 6 O2.

[0032] Example 2 A manganese-based layered oxide with an ordered and disordered mixed structure is prepared by the following steps: 1) Dissolve 0.21 mol of anhydrous sodium hydroxide, 0.05 mol of magnesium acetate tetrahydrate, 0.25 mol of manganese acetate tetrahydrate and 0.3 mol of citric acid in 0.3 L of water, mix well, and obtain a precursor mixture; mix well, and obtain a precursor mixture; 2) heating the precursor mixture to 90°C and evaporating to dryness to obtain a precursor; 3) After the precursor is ground into powder, it is pre-sintered at 500 °C in air for 2 h, and then sintered at 900 °C in oxygen atmosphere for 10 h to obtain a manganese-based layered oxide Na with a mixed structure of ordered and disordered structures. 2 / 3 Mg 1 / 6 Mn 5 / 6 O2.

[0033] Example 3 A manganese-based layered oxide with an ordered and disordered mixed structure is prepared by the following steps: 1) Dissolve 0.2 mol sodium acetate trihydrate, 0.05 mol magnesium acetate tetrahydrate, 0.25 mol manganese acetate tetrahydrate and 0.5 mol glycolic acid in 0.3 l water and mix well to obtain a precursor mixture; 2) heating the precursor mixture to 70°C and evaporating to dryness to obtain a precursor; 3) After the precursor is ground into powder, it is pre-sintered at 400 °C in air for 6 h, and then sintered at 800 °C in oxygen atmosphere for 20 h to obtain a manganese-based layered oxide Na with a mixed structure of ordered and disordered structures. 2 / 3 Mg 1 / 6 Mn 5 / 6 O2.

[0034] Example 4 A manganese-based layered oxide with an ordered and disordered mixed structure is prepared by the following steps: 1) Dissolve 0.2 mol of anhydrous sodium nitrate, 0.05 mol of anhydrous magnesium acetate, 0.25 mol of anhydrous manganese nitrate and 0.3 mol of glycolic acid in 0.3 L of water and mix well to obtain a precursor mixture; 2) heating the precursor mixture to 95°C and evaporating to dryness to obtain a precursor; 3) After the precursor is ground into powder, it is pre-sintered at 550 °C in air for 5 h, and then sintered at 750 °C in oxygen atmosphere for 20 h to obtain a manganese-based layered oxide Na with a mixed structure of ordered and disordered structures. 2 / 3 Mg 1 / 6 Mn 5 / 6 O2.

[0035] Figure 1 The XRD and refined patterns of the manganese-based layered oxide with a mixed structure of ordered and disordered structures prepared in this example. From the XRD pattern, it can be seen that the material belongs to the P2 phase. Further combined with the refinement results, it is found that it contains two phase structures, one is the Na2 phase composed of ordered units -Mg-Mn-Mn 2 / 3 Mg 1 / 3 Mn 2 / 3 O2 phase, and the other is Na composed of disordered units -Mn-Mn-Mn 2 / 3 MnO2 phase, in which the two phases are in a ratio of 4:1, confirming the Na 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 is a mixed structure of order and disorder.

[0036] Figure 2 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in this embodiment 2 / 3 Mg 1 / 6 Mn 5 / 6 The SEM image of O2 shows that the grain shape is plate-like and the particle size is 1~2μm.

[0037] Figure 3 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in this embodiment 2 / 3 Mg 1 / 6 Mn 5 / 6X-ray energy dispersion spectrum of O2 shows that the four elements Na, Mg, Mn, and O are evenly distributed throughout the particle.

[0038] The ordered and disordered mixed structure manganese-based layered oxide Na 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 is used as the positive electrode active material of the sodium ion battery and assembled into a button battery. The specific operation method is: the manganese-based layered oxide Na 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 was mixed evenly with carbon black conductive agent and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1 and dispersed in N-methylpyrrolidone (NMP) and stirred to form a slurry. The slurry was evenly coated on aluminum foil, dried and cut into electrode sheets, and assembled into button cells together with sodium sheets, glass fiber separators and sodium electrolyte (1 mol / L NaPF6 dissolved in DMC / EC / DEC with a volume ratio of 1:1:1) for electrochemical performance testing.

[0039] Figure 4 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in this example 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Comparison of charge and discharge curves of different cycles under O20.1C. As can be seen from the figure, the capacity of the two is similar in the first cycle. As the cycle progresses, Na 2 / 3 Mg 1 / 3 Mn 2 / 3 The shape of the charge and discharge curve of O2 is constantly changing, and the original oxygen platform disappears. 2 / 3 Mg 1 / 6 Mn 5 / 6 For O2, the charge-discharge curve does not change much, and the oxygen platform is still maintained even after 50 cycles. This shows that the ordered-disordered mixed structure greatly improves the reversibility and stability of the oxygen-redox reaction process.

[0040] Figure 5 The ordered and disordered mixed structure of manganese-based layered oxide Na prepared in Example 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Capacity comparison of 50 cycles of O2 at 0.1C.2 / 3 Mg 1 / 6 Mn 5 / 6 O2 vs Na 2 / 3 Mg 1 / 3 Mn 2 / 3 O2 has a higher capacity. Even after 50 cycles, it still has 186.21mAh g -1 The ultrahigh capacity of the 2-Hydrogen-Oxy ...-Oxy-

[0041] Figure 6 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Comparison of discharge average voltage after 200 cycles of O21C. Similar to most anion reactive layered oxides, Na 2 / 3 Mg 1 / 3 Mn 2 / 3 The voltage of O2 decays very quickly, from 2.60 to 2.28V. 2 / 3 Mg 1 / 6 Mn 5 / 6 The voltage of O2 has almost no attenuation, only 0.19mV per cycle, which shows that the ordered and disordered mixed structure can effectively solve the voltage drop problem.

[0042] Figure 7 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3 Capacity comparison of 200 cycles under O21C. At a higher current density (150 mAg -1 ), Na 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 still shows better stability and capacity retention.

[0043] Figure 8 The manganese-based layered oxide Na with a mixed structure of ordered and disordered structures prepared in Example 1 2 / 3 Mg 1 / 6 Mn 5 / 6 O2 and the common single ordered structure of manganese-based layered oxides Na 2 / 3 Mg 1 / 3 Mn 2 / 3Comparison of high-angle annular dark field images of O2 charged to 4.5V. It can be seen that under high voltage, Na 2 / 3 Mg 1 / 3 Mn 2 / 3 The structure of O2 is severely damaged, and a large number of intracrystalline cracks appear. 2 / 3 Mg 1 / 6 Mn 5 / 6 The entire O2 particle remains intact, indicating that the ordered and disordered mixed structure effectively suppresses interlayer slip and lattice stress, and enhances the structural stability of the material.

[0044] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A manganese-based layered oxide having a mixed structure, characterized in that: The chemical formula of manganese-based layered oxide is Na 1- x M y Mn 1-y O2, 0<x<1, 0<y<1, belongs to the P2 phase, M is one or more of Mg, Fe, Al, Zn, Co, Ni, and Cu, and the mixed structure includes an ordered structure and a disordered structure, wherein in the ordered structure, two manganese atoms plus one M atom are arranged in the atomic form of -M-Mn-M- as the basic repeating unit; in the disordered structure, continuous manganese atoms -Mn-Mn-Mn- are arranged in the atomic form of the basic repeating unit.

2. The manganese-based layered oxide having a mixed structure according to claim 1, characterized in that: The average particle size of the manganese-based layered oxide is ~2 μm, and the grain shape is plate-like.

3. A method for preparing a manganese-based layered oxide having a mixed structure as claimed in claim 1 or 2, characterized in that: The steps include: 1) dissolving sodium salt, M salt, manganese salt and organic chelating agent in water and mixing them evenly to obtain a precursor mixed solution; 2) heating the precursor mixture to dryness to obtain a precursor; 3) After the precursor is ground into powder, it is pre-fired in air and then sintered in air or oxygen atmosphere to obtain a manganese-based layered oxide with an ordered and disordered mixed structure.

4. The preparation method according to claim 3, characterized in that: The sodium salt is one or more of anhydrous sodium nitrate, anhydrous sodium acetate, anhydrous sodium hydroxide, and sodium acetate trihydrate.

5. The preparation method according to claim 3, characterized in that: The M salt is one or more of anhydrous nitrate, anhydrous acetate, hexahydrate nitrate, and tetrahydrate acetate.

6. The preparation method according to claim 3, characterized in that: Step 1) The manganese salt is one or more of anhydrous manganese nitrate, anhydrous manganese acetate, manganese nitrate tetrahydrate, and manganese acetate tetrahydrate.

7. The preparation method according to claim 3, characterized in that: The organic chelating agent is one or more of citric acid and glycolic acid.

8. The preparation method according to claim 3, characterized in that: The molar ratio of the sodium salt, M salt, manganese salt, and organic chelating agent is (0.2-0.21): 0.05: 0.25: 0.3; the volume of water is 0.1-1L.

9. The preparation method according to claim 3, characterized in that: The heating temperature in step 2) is 70-95°C; the pre-sintering temperature in step 3) is 400-550°C, and the pre-sintering time is 2-6h; when the sintering temperature is 750-900°C, the sintering time is 10-20h.

10. Use of the manganese-based layered oxide with a mixed structure as claimed in claim 1 or 2 or the manganese-based layered oxide prepared by the method according to any one of claims 3 to 9 as a positive electrode active material for a sodium ion battery.

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