A full-manganese-based layered oxide having a vacancy-ordered superstructure and a preparation method and application thereof

Abstract

The application belongs to the technical field of battery materials and electrochemistry, and discloses a full-manganese-based layered oxide with a vacancy-ordered superstructure and a preparation method and application thereof.The full-manganese-based layered oxide has a chemical formula of Na2Mn3O7, and its structure comprises sodium ion layers and manganese ion layers which are alternately arranged in sequence, the sodium ion layers and the manganese ion layers are bridged by oxygen, and the manganese ion layer has a vacancy-ordered superstructure of Mn-Mn-Mn-Mn-□, so that the manganese ion layer and the sodium ion layer locally form a Na-O-□ configuration when they are bridged.The full-manganese-based layered oxide has the vacancy-ordered superstructure, so that when the full-manganese-based layered oxide is used as a positive active material of a sodium ion battery, the capacity and reversibility contributed by the oxygen redox reaction can be significantly improved, and the voltage hysteresis caused by the oxygen redox reaction can be significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of battery materials and electrochemical technology, specifically relating to a fully manganese-based basal oxide with a vacancy-ordered superstructure, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices and electric vehicles. The expansion of the electric vehicle market will inevitably lead to the rapid depletion of lithium resources. Furthermore, the uneven distribution of lithium resources worldwide increases the cost of lithium-ion batteries. These factors limit the application of lithium-ion batteries in large-scale energy storage systems. As a promising alternative to lithium-ion batteries, sodium-ion batteries have attracted increasing attention due to the high abundance and low cost of sodium in the Earth's crust. Among these, layered oxides are currently a research hotspot for cathode materials in sodium-ion batteries, and improving the low capacity limitation of layered oxides is a problem that urgently needs to be solved.

[0003] Traditional charge compensation in cathodes is based on redox pairs of transition metals, with Ni being a common example. 2+ / Ni 3 + Ni 3+ / Ni 4+ Co 3+ / Co 4+ Fe 3+ / Fe 4+ Cu 2+ / Cu 3+ Mn 3+ / Mn 4+ And so on, while the energy density of the positive electrode is mainly limited by the content of variable-valence transition metals. For example, LiCoO2 is produced through Co... 3+ / 4+ To provide Li + Only with charge compensation from insertion / extraction can it achieve a capacity of only 150 mAh g. -1 The actual capacity. Around 2000, researchers discovered that lithium-rich manganese-based materials like Li₂MnO₃ possessed ultra-high capacities exceeding theoretical limits. Further research revealed that the additional capacity was provided by lattice oxygen (O) in the bulk phase. Due to the extremely high specific energy of lithium-rich materials, research on these materials has remained consistently popular. Since 2015, sodium-ion battery cathode materials with O redox properties have been reported, and this mechanism may further improve the energy density of sodium-ion batteries.

[0004] Li₂MnO₃ is believed to possess oxygen activity due to its unhybridized Li-O-Li configuration. However, researchers have also discovered oxygen activity in other cathode materials with special configurations such as Na-O-Li, Na-O-Mg, and Na-O-□ (□ refers to a cation vacancy). Conventionally prepared NaMnO₂ and Na...2 / 3 MnO2 does not possess the aforementioned special oxygen configuration, and therefore cannot stimulate oxygen activity. Thus, how to significantly improve the cathode capacity by introducing cation vacancies into the transition metal layer to construct a special Na-O-□ configuration and stimulate oxygen redox reactivity without doping with highly ionic elements such as Li and Mg has become a challenging research topic. This research provides guidance for improving the capacity of layered oxides using oxygen redox reactions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a full manganese base layer oxide with a vacancy-ordered superstructure, its preparation method and application. Introducing cation vacancies into the transition metal layer of the full manganese base layer oxide gives it a vacancy-ordered superstructure, thereby locally forming a Na-O-□ configuration. When used as a positive electrode active material for sodium-ion batteries, it can significantly improve the capacity and reversibility contributed by the oxygen redox reaction and significantly reduce the voltage hysteresis caused by the oxygen redox reaction.

[0006] To address the technical problem proposed in this invention, this invention provides a fully manganese-based crystalline oxide with a vacancy-ordered superstructure, the chemical formula of which is Na2Mn3O7. Its structure includes alternating sodium ion layers and manganese ion layers, which are bridged by oxygen. The manganese ion layer has a vacancy-ordered superstructure, thereby locally forming a Na-O-□ configuration (□ refers to a cation vacancy) when the manganese ion layer is bridged with the sodium ion layer.

[0007] In the above scheme, the vacancy-ordered superstructure is a special atomic arrangement Mn-Mn-Mn-Mn-□ (□ refers to a cation vacancy) with four manganese atoms plus one cation vacancy as the basic repeating unit.

[0008] In the above scheme, the phase structure of the all-manganese base oxide is a pure P2 phase or a pure P3 phase, and the phase structure is controlled by adjusting the sintering temperature.

[0009] In the above scheme, when the all-manganese base oxide is a pure P2 phase, the grain shape is plate-shaped and the grain size is 3-5μm; when the all-manganese base oxide is a pure P3 phase, the grain shape is spherical and the grain size is 300-500nm.

[0010] This invention also provides a method for preparing a fully manganese-based base oxide with a vacancy-ordered superstructure, comprising the following steps:

[0011] 1) Dissolve sodium salt, manganese salt and organic chelating agent in water, mix well to obtain precursor mixture;

[0012] 2) Heat the precursor mixture to dryness to obtain the precursor;

[0013] 3) After grinding the precursor into powder, it is first pre-fired in air and then sintered in air or oxygen atmosphere to obtain a full manganese base layer oxide with vacancy-ordered superstructure.

[0014] In the above scheme, the sodium salt is one of anhydrous sodium nitrate, anhydrous sodium acetate, anhydrous sodium hydroxide, and sodium acetate trihydrate.

[0015] In the above scheme, the manganese salt is one of anhydrous manganese nitrate, anhydrous manganese acetate, manganese nitrate tetrahydrate, and manganese acetate tetrahydrate.

[0016] In the above scheme, the organic chelating agent is one of citric acid and glycolic acid.

[0017] In the above scheme, the molar ratio of sodium salt, manganese salt and organic chelating agent is (0.6-0.75):1:(0.5-5).

[0018] In the above scheme, the molar ratio of sodium salt to water in step 1) is (0.1-5) mol: 1L.

[0019] In the above scheme, the heating temperature in step 2) is 70-95℃.

[0020] In the above scheme, the pre-firing temperature is 400-550℃ and the pre-firing time is 2-6h.

[0021] In the above scheme, the sintering temperature is 450-850℃ and the sintering time is 10-20h.

[0022] In the above scheme, when the sintering temperature is 450-750℃, a pure P3 phase is obtained; when the sintering temperature is 750-850℃ (excluding 750℃), a pure P2 phase is obtained.

[0023] The present invention also provides an application of a fully manganese-based morphological oxide with a vacancy-ordered superstructure, wherein the fully manganese-based morphological oxide is used as a positive electrode active material for sodium-ion batteries.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) This invention is the first to synthesize a novel all-manganese-based layered oxide, Na2Mn3O7, with a vacancy-ordered superstructure. This vacancy-ordered superstructure is a special atomic arrangement, Mn-Mn-Mn-Mn-□ (□ refers to a cation vacancy), with four manganese atoms and one cation vacancy as the basic repeating unit. This allows for the construction of a Na-O-□ configuration without doping with highly ionic elements such as Li and Mg. Therefore, when used as a positive electrode active material for sodium-ion batteries, it can significantly improve the capacity and reversibility contributed by the oxygen redox reaction. Compared with other positive electrode materials involving oxygen redox reactions, these two materials have higher capacity and better reversibility of the oxygen redox reaction, and the voltage hysteresis caused by the oxygen redox reaction is significantly reduced.

[0026] 2) The sol-gel method used in this invention is simple and easy to implement, and can obtain pure P2 phase and pure P3 phase all-manganese base oxide Na2Mn3O7 with regular morphology and uniform size. Furthermore, the phase structure can be controlled by adjusting the sintering temperature to meet actual needs. Attached Figure Description

[0027] Figure 1 This is the XRD pattern of the all-manganese base oxide with a vacancy-ordered superstructure prepared in Example 1.

[0028] Figure 2 This is a SEM image of the all-manganese base oxide with a vacancy-ordered superstructure prepared in Example 1.

[0029] Figure 3 These are HAADF STEM images and corresponding SAED patterns of all-manganese base layer oxides with vacancy-ordered superstructures prepared in Example 1.

[0030] Figure 4 The above are the charge-discharge curves of a coin cell assembled using the all-manganese base layer oxide with a vacancy-ordered superstructure prepared in Example 1 as the cathode material for a sodium-ion battery.

[0031] Figure 5 This is the XRD pattern of the all-manganese base oxide with a vacancy-ordered superstructure prepared in Example 2.

[0032] Figure 6 This is a SEM image of the all-manganese base oxide with a vacancy-ordered superstructure prepared in Example 2.

[0033] Figure 7 The images shown are HAADF STEM images and corresponding SAED patterns of all-manganese base layer oxides with vacancy-ordered superstructures prepared in Example 2.

[0034] Figure 8The above are the charge-discharge curves of a coin cell assembled using the all-manganese base layer oxide with a vacancy-ordered superstructure prepared in Example 2 as the cathode material for a sodium-ion battery.

[0035] Figure 9 These are XRD patterns of all-manganese base oxides with vacancy-ordered superstructures obtained at different sintering temperatures. Detailed Implementation

[0036] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0037] Example 1

[0038] A fully manganese-based base oxide with a vacancy-ordered superstructure is prepared by the following steps:

[0039] 1) Dissolve 0.2 mol anhydrous sodium acetate, 0.3 mol manganese acetate tetrahydrate and 0.3 mol citric acid in 0.5 L of water and mix well to obtain a precursor mixture;

[0040] 2) Heat the precursor mixture to 80°C and evaporate to dryness to obtain the precursor;

[0041] 3) After grinding the precursor into powder, it is first pre-calcined in air at 450°C for 4 hours, and then sintered in air at 850°C for 12 hours to obtain a full-manganese base oxide with a vacancy-ordered superstructure.

[0042] Figure 1 This is the XRD pattern of the all-manganese base layer oxide with vacancy-ordered superstructure prepared in this embodiment. As can be seen from the figure, the all-manganese base layer oxide in this embodiment is a pure P2 phase Na2Mn3O7. From the magnified view, many superstructure peaks can be seen between 10-30°, which is significantly different from the traditional P2 phase. These superstructure peaks indicate that there is an ordered arrangement of Mn and cation vacancies in its transition metal layer (i.e., manganese ion layer).

[0043] Figure 2 This is a SEM image of the all-manganese base layer oxide with vacancy-ordered superstructure prepared in this embodiment. As can be seen from the image, the pure P2 phase all-manganese base layer oxide Na2Mn3O7 synthesized in this embodiment has a disc-shaped grain shape and a grain size of 3-5 μm.

[0044] Figure 3These are HAADF STEM images and corresponding SAED patterns of the all-manganese base layer oxide with a vacancy-ordered superstructure prepared in this embodiment. As can be directly seen from the images, the pure P2-phase all-manganese base layer oxide Na2Mn3O7 synthesized in this embodiment possesses a vacancy-ordered superstructure, which is a special atomic arrangement Mn-Mn-Mn-Mn-□ with four manganese atoms plus one cation vacancy as the basic repeating unit, where □ represents a cation vacancy. The sodium ion layer and the manganese ion layer are bridged by oxygen. When the bridge is the □ of the manganese ion layer, a Na-O-□ configuration is locally formed. The additional superstructure diffraction points between the diffraction points of the layered structure in the SAED also prove the existence of a uniform vacancy-ordered superstructure within a single particle.

[0045] The all-manganese base oxide with vacancy-ordered superstructure prepared in this embodiment is used as the positive electrode active material of sodium-ion battery and assembled into a coin cell. The specific operation method is as follows: the above-mentioned all-manganese base oxide material with vacancy-ordered superstructure is mixed with carbon black conductive agent and polyvinylidene fluoride (PVDF) binder at a mass ratio of 8:1:1 and dispersed in N-methylpyrrolidone (NMP) and stirred to form a slurry. The slurry is uniformly coated on aluminum foil, dried and cut into electrode sheets, and assembled into a coin cell together with sodium sheet, glass fiber separator and sodium electrolyte (1 mol / L NaPF6 dissolved in DMC / EC / DEC at a volume ratio of 1:1:1).

[0046] A constant current charge-discharge test was performed on the coin cell. Figure 4 This coin cell operates at a current density of 15 mAg. -1 The 20-cycle charge-discharge curves within the voltage range of 1.5-4.5V show that during the first charge cycle, the P2 phase Na2Mn3O7 can provide 149.5 mAh / g. -1 The capacity is high; during discharge, the oxygen plateau of P2 phase Na2Mn3O7 can be maintained, indicating strong reversibility of oxygen redox. Within a voltage range of 1.5-4.5V, P2 phase Na2Mn3O7 exhibits a capacity as high as 205mAh g / g. -1 The specific capacity, after 20 cycles, is 148.2 mAh g. -1 This capacity is relatively advantageous among sodium-ion battery cathode materials, which is attributed to the locally formed Na-O-□ configuration stabilizing the redox reaction of oxygen.

[0047] Example 2

[0048] A fully manganese-based base oxide with a vacancy-ordered superstructure is prepared by the following steps:

[0049] 1) Dissolve 0.2 mol anhydrous sodium hydroxide, 0.3 mol manganese acetate tetrahydrate and 1.5 mol citric acid in 2 L of water and mix well to obtain a precursor mixture;

[0050] 2) Heat the precursor mixture to 90°C and evaporate to dryness to obtain the precursor;

[0051] 3) After grinding the precursor into powder, it is first pre-calcined in air at 500°C for 2 hours, and then sintered at 700°C in an oxygen atmosphere for 20 hours to obtain a full-manganese base oxide with a vacancy-ordered superstructure.

[0052] Figure 5 This is the XRD pattern of the all-manganese base layer oxide with vacancy-ordered superstructure prepared in this embodiment. As can be seen from the figure, the all-manganese base layer oxide in this embodiment is pure P3 phase Na2Mn3O7. From the magnified view, it can also be seen that there are many superstructure peaks between 10-30°, which also indicates that there is an ordered arrangement of Mn and cation vacancies in its transition metal layer (i.e., manganese ion layer).

[0053] Figure 6 This is a SEM image of the all-manganese base layer oxide with vacancy-ordered superstructure prepared in this embodiment. As can be seen from the image, the pure P3 phase all-manganese base layer oxide Na2Mn3O7 synthesized in this embodiment has a spherical grain shape and a grain size of 300-500 nm.

[0054] Figure 7 These are HAADF STEM images and corresponding SAED patterns of the all-manganese base layer oxide with a vacancy-ordered superstructure prepared in this embodiment. As can be seen from the images, the pure P3 phase all-manganese base layer oxide Na2Mn3O7 synthesized in this embodiment possesses a vacancy-ordered superstructure, which is a special atomic arrangement Mn-Mn-Mn-Mn-□ with four manganese atoms plus one cation vacancy as the basic repeating unit, where □ represents a cation vacancy. The bridging oxygen in some sodium and manganese ion layers also forms a Na-O-□ configuration. The additional superstructure diffraction points between the layered diffraction points in the SAED also prove the existence of a uniform vacancy-ordered superstructure within a single particle.

[0055] The all-manganese base oxide with vacancy-ordered superstructure prepared in this embodiment is used as the positive electrode active material of sodium-ion battery and assembled into a coin cell. The specific operation method is as follows: the above-mentioned all-manganese base oxide material with vacancy-ordered superstructure is mixed with carbon black conductive agent and polyvinylidene fluoride (PVDF) binder at a mass ratio of 8:1:1 and dispersed in N-methylpyrrolidone (NMP) and stirred to form a slurry. The slurry is uniformly coated on aluminum foil, dried and cut into electrode sheets, and assembled into a coin cell together with sodium sheet, glass fiber separator and sodium electrolyte (1 mol / L NaPF6 dissolved in DMC / EC / DEC at a volume ratio of 1:1:1).

[0056] A constant current charge-discharge test was performed on the coin cell. Figure 8 This coin cell operates at a current density of 15 mAg. -1 The 20-cycle charge-discharge curves within the voltage range of 1.5-4.5V show that during the first charge cycle, the P3 phase Na2Mn3O7 can provide 142mAh g / kg. -1 The capacity; the oxygen plateau of the P3 phase Na2Mn3O7 during the first discharge is 68 mAh g. -1 The specific capacity of P3 phase Na2Mn3O7 is high, and the oxygen plateau can be maintained, indicating strong reversibility of oxygen redox and a very small voltage hysteresis of only 0.12V. P3 phase Na2Mn3O7 discharges to 1.5V in the first cycle, with a specific capacity as high as 215mAhg. -1 Furthermore, the capacity of the P3 phase remained stable at 180.5 mAh after 20 cycles. -1 The capacity retention rate is 83.9%, and this excellent oxygen redox stability is due to the Na-O-□ configuration formed locally in the structure.

[0057] Example 3

[0058] A fully manganese-based base oxide with a vacancy-ordered superstructure is prepared by the following steps:

[0059] 1) Dissolve 0.22 mol sodium acetate trihydrate, 0.3 mol manganese nitrate tetrahydrate and 0.5 mol glycolic acid in 50 ml of water and mix well to obtain a precursor mixture;

[0060] 2) Heat the precursor mixture to 70°C and evaporate to dryness to obtain the precursor;

[0061] 3) After grinding the precursor into powder, it is first pre-calcined in air at 400℃ for 6 hours, and then sintered at 450℃ in an oxygen atmosphere for 20 hours to obtain a full manganese base layer oxide with a vacancy-ordered superstructure.

[0062] Example 4

[0063] A fully manganese-based base oxide with a vacancy-ordered superstructure is prepared by the following steps:

[0064] 1) Dissolve 0.2 mol anhydrous sodium nitrate, 0.3 mol manganese nitrate tetrahydrate and 0.15 mol citric acid in 200 ml of water and mix well to obtain a precursor mixture;

[0065] 2) Heat the precursor mixture to 95°C and evaporate to dryness to obtain the precursor;

[0066] 3) After grinding the precursor into powder, it is first pre-calcined in air at 550°C for 5 hours, and then sintered at 650°C in an oxygen atmosphere for 18 hours to obtain a full-manganese base oxide with a vacancy-ordered superstructure.

[0067] Figure 9 These are XRD patterns of all-manganese base-like oxides with vacancy-ordered superstructures obtained at different sintering temperatures. The figures show that above 750℃, pure P2 phase Na2Mn3O7 is formed, while below 750℃, pure P3 phase Na2Mn3O7 is formed.

[0068] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A fully manganese-based base oxide with a vacancy-ordered superstructure, characterized in that, Its chemical formula is Na2Mn3O7. Its structure includes alternating sodium ion layers and manganese ion layers, which are bridged by oxygen. The manganese ion layer has a vacancy-ordered superstructure, which is a special atomic arrangement Mn-Mn-Mn-Mn-□ with four manganese atoms plus one cation vacancy as the basic repeating unit. Thus, when the manganese ion layer and the sodium ion layer are bridged, a Na-O-□ configuration is locally formed, where □ refers to a cation vacancy. The method for preparing the all-manganese base oxide with a vacancy-ordered superstructure includes the following steps: 1) Dissolve sodium salt, manganese salt and organic chelating agent in water, wherein the organic chelating agent is citric acid or glycolic acid, and the molar ratio of sodium salt, manganese salt and organic chelating agent is (0.6-0.75):1:(0.5-2), mix evenly to obtain precursor mixture; 2) The precursor mixture is heated and evaporated to dryness to obtain the precursor; 3) After grinding the precursor into powder, it is first pre-fired in air at a temperature of 400-550℃ for 2-6 hours; then sintered in air or oxygen atmosphere at a temperature of 450-850℃ for 10-20 hours to obtain a full manganese base oxide with a vacancy-ordered superstructure. The phase structure of the all-manganese base oxide is either a pure P2 phase or a pure P3 phase. The phase structure is controlled by adjusting the sintering temperature: when 450℃≤sintering temperature≤750℃, a pure P3 phase is obtained; when 750℃<sintering temperature≤850℃, a pure P2 phase is obtained.

2. The all-manganese base-like oxide with a vacancy-ordered superstructure according to claim 1, characterized in that, When the all-manganese base oxide is a pure P2 phase, the grain shape is disc-shaped with a grain size of 3-5 μm; when the all-manganese base oxide is a pure P3 phase, the grain shape is spherical with a grain size of 300-500 nm.

3. A method for preparing a fully manganese-based base oxide with a vacancy-ordered superstructure as described in claim 1, characterized in that, Includes the following steps: 1) Dissolve sodium salt, manganese salt and organic chelating agent in water, wherein the organic chelating agent is citric acid or glycolic acid, and the molar ratio of sodium salt, manganese salt and organic chelating agent is (0.6-0.75):1:(0.5-2), mix evenly to obtain precursor mixture; 2) The precursor mixture is heated and evaporated to dryness to obtain the precursor; 3) After grinding the precursor into powder, it is first pre-fired in air at a temperature of 400-550℃ for 2-6 hours; then sintered in air or oxygen atmosphere at a temperature of 450-850℃ for 10-20 hours to obtain a full manganese base oxide with a vacancy-ordered superstructure. The phase structure of the all-manganese base oxide is either a pure P2 phase or a pure P3 phase. The phase structure is controlled by adjusting the sintering temperature: when 450℃≤sintering temperature≤750℃, a pure P3 phase is obtained; when 750℃<sintering temperature≤850℃, a pure P2 phase is obtained.

4. The method for preparing a fully manganese-based substrate oxide with a vacancy-ordered superstructure according to claim 3, characterized in that, The sodium salt is one of anhydrous sodium nitrate, anhydrous sodium acetate, anhydrous sodium hydroxide, and sodium acetate trihydrate; the manganese salt is one of anhydrous manganese nitrate, anhydrous manganese acetate, manganese nitrate tetrahydrate, and manganese acetate tetrahydrate.

5. The method for preparing a fully manganese-based substrate oxide with a vacancy-ordered superstructure according to claim 3, characterized in that, In step 1), the molar ratio of sodium salt to water is (0.1-5) mol: 1L.

6. The application of a full manganese base oxide with a vacancy-ordered superstructure as described in any one of claims 1-2, or a full manganese base oxide with a vacancy-ordered superstructure prepared by the preparation method described in any one of claims 3-5, in a sodium-ion battery.

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