A high-stability layered oxide sodium-ion battery cathode active material and a preparation method thereof

Abstract

This invention relates to a highly stable layered oxide sodium-ion battery cathode active material and its preparation method. The chemical formula of the cathode active material is K. x Na y Cu α Ni β Mn 0.6 In the chemical formula O2, x represents the K doping amount; α represents the Cu doping amount; and β represents the Ni doping amount, where 0 ≤ x ≤ 0.35, 0.32 ≤ y ≤ 0.67, 0 ≤ α ≤ 0.4, 0 ≤ β ≤ 0.4, and x + y = 0.67, α + β = 0.4; the positive electrode active material exhibits a layered stacked morphology. This invention employs a novel bi-site substitution strategy, namely, large-radius K... + Riveted to prismatic Na + Position, Cu 2+ Occupied in transition metal sites; large radius K + Occupy Na + The presence of these sites results in larger interlayer spacing, providing more sodium ion storage sites and faster ion transport channels. Furthermore, K... + The larger interlayer spacing resulting from doping corresponds to a multilayered, oriented stacking of nanosheets in the microstructure, which is beneficial for sodium ion transport. This invention possesses high Cu content. 2+ / Cu 3+ Cu substitution with a high redox potential improves the stability of the material when exposed to air and water.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a highly stable layered oxide sodium-ion battery positive electrode active material and its preparation method. Background Technology

[0002] Sodium-ion batteries have significant advantages and promising prospects for large-scale energy storage applications due to their low cost, abundant natural resources, and electrochemical performance similar to lithium-ion batteries.

[0003] The specific capacity of positive electrode active materials for sodium-ion batteries is still far lower than that of negative electrode materials. Therefore, developing high-performance positive electrode active materials is key to promoting the large-scale application of sodium-ion batteries. Currently, sodium-ion positive electrode active materials mainly include four categories: sodium-based transition metal oxides, Prussian blue, polyanionic materials, organic molecules, and polymers.

[0004] Sodium-based transition metal oxides are considered one of the most promising cathode active materials for sodium-ion batteries for commercialization. However, during the production process of sodium-based transition metal oxides, exposure to air or water for a period of time leads to severe degradation of electrochemical performance, which limits their commercialization. Summary of the Invention

[0005] In view of the problem that the electrochemical performance of sodium-based transition metal oxides degrades severely after exposure to air or water for a period of time during the production process, the present invention aims to provide a highly stable layered oxide sodium-ion battery positive electrode active material and its preparation method. This positive electrode active material has the characteristics of good stability, excellent rate performance and long cycle life.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A highly stable layered oxide cathode active material for sodium-ion batteries, the chemical formula of which is K. x Na y Cu α Ni β Mn 0.6 O2, in the chemical formula:

[0008] x represents the K doping amount; α represents the Cu doping amount; β represents the Ni doping amount, where 0≤x≤0.35, 0.32≤y≤0.67, 0≤α≤0.4, 0≤β≤0.4, and x+y=0.67, α+β=0.4;

[0009] The positive electrode active material has a layered stacked structure at the microscopic level.

[0010] In the preferred embodiment, the positive electrode active material has a P2-type crystal structure with two types of sodium ion sites, namely Na e and Na f The ratio of sodium ions is Na e Na f = 0.32:0.35. The crystal structure of the positive electrode active material has a hexagonal close-packed structure with space group P63 / mmc.

[0011] In a preferred embodiment, the X-ray diffraction of the positive electrode active material includes characteristic peaks of the (100) crystal plane and characteristic peaks of the (002) crystal plane; the interlayer spacing of the (002) crystal plane of the positive electrode active material is...

[0012] In the preferred embodiment, the average particle size D of the positive electrode active material is... v 50 is 0.5-10μm.

[0013] In the preferred embodiment, after the positive electrode active material is exposed to air for more than one month, its electrochemical capacity decay is less than 5% compared to the positive electrode active material that is not exposed to air.

[0014] In the preferred embodiment, after the positive electrode active material is exposed to an aqueous environment for more than 24 hours, its electrochemical capacity decay is less than 5% compared to the positive electrode active material that is not exposed to an aqueous environment.

[0015] By placing the positive electrode active material in an air environment or a pure aqueous solution, the stability of the positive electrode active material can be investigated, as the material easily absorbs water and agglomerates.

[0016] As a general inventive concept, this invention also provides a method for preparing a highly stable layered oxide sodium-ion battery positive electrode active material, comprising the following steps:

[0017] (1) Prepare a mixed salt solution by mixing potassium salt, sodium salt, manganese salt, nickel salt, and copper salt in a predetermined ratio, and add...

[0018] Citric acid is dissolved in water, and the solution is evaporated by hydrothermal evaporation to obtain a sol-gel. The obtained gel is then dried and ground to obtain a solid powder.

[0019] (2) The solid powder obtained in step (1) is placed in an air atmosphere for the first stage of heating and calcination. The first stage of heating and calcination removes the organic components in the precursor. After the temperature drops to room temperature, the obtained sample is ground into a uniform powder.

[0020] (3) The uniform powder obtained in step (2) is pressed into tablets, and then the tablet sample is placed in an air atmosphere for a second stage of heating and calcination. After the temperature drops to room temperature, the block sample is ground into powder again to obtain the high-stability layered oxide sodium-ion battery positive electrode active material.

[0021] The preferred approach is to use a two-stage heating method, which is more conducive to the phase formation of layered oxide materials. In the first stage of heating, the organic components in the precursor are removed in the form of CO2 to form oxides. The second stage of heating is the phase formation process of layered metal oxides. Before this heating process, the sample after the first stage of heating is ground into fine particles and then pressed into a tablet to increase the contact area between the particles, which is more conducive to the phase formation of layered oxides.

[0022] Further preferred, the conditions for the first stage of heating and calcination are: the powder is heated in a muffle furnace at 5°C for 1 minute. -1 The heating rate is increased to 300-400℃, and the temperature is maintained for 6-12 hours;

[0023] The conditions for the second stage of heating and calcination are: the powder is heated in a muffle furnace at 5°C for 1 minute. -1 The heating rate is increased to 400-900℃, and the temperature is maintained for 6-12 hours;

[0024] The second stage of heating and calcination is at a higher temperature than the first stage, and heating to a higher temperature is beneficial for phase formation.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] (1) This invention provides a highly stable layered oxide sodium-ion battery cathode active material, which utilizes a novel dual-site substitution strategy, namely, a large-radius K... + Riveted to prismatic Na + Position, Cu 2+ Occupied in transition metal sites; large radius K + Occupy Na + The presence of these sites results in larger interlayer spacing, providing more sodium ion storage sites and faster ion transport channels. Furthermore, K... + The larger interlayer spacing caused by doping corresponds to the multilayer oriented stacking of nanosheets in the microstructure, which is beneficial to the transport of sodium ions.

[0027] (2) The present invention provides a high-stability layered oxide sodium-ion battery positive electrode active material with high Cu content. 2+ / Cu 3+ Cu substitution with a high redox potential improves the stability of the material when exposed to air and water.

[0028] (3) The present invention provides a method for preparing a highly stable layered oxide sodium-ion battery positive electrode active material, wherein the prepared layered stacked P2-K 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 O2 exhibits excellent rate performance, rapid sodium ion transport capacity, and superior cycling performance in 1 Ag. -1 At high current density, after 1800 cycles, its capacity retention rate is as high as 91.2%. Attached Figure Description

[0029] Figure 1 Na in Comparative Example 1 0.67 Mn 0.6 Ni 0.3 Cu 0.1 The refined XRD image of O2.

[0030] Figure 2 K in Example 1 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1 The refined XRD image of O2.

[0031] Figure 3 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 SEM image of O2.

[0032] Figure 4 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 TEM image of O2.

[0033] Figure 5 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 STEM image of O2 (with corresponding (101) crystal planes marked).

[0034] Figure 6 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6STEM image of O2 (with corresponding (002) crystal planes marked).

[0035] Figure 7 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 EDS mapping diagram of O2.

[0036] Figure 8 It is K x Na 0.67-x Cu 0.1 Ni 0.3 Mn 0.6 Rate performance diagram of O2 series layered oxide cathode active materials.

[0037] Figure 9 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 O2 in 1Ag -1 Long-term cycling stability under high current density.

[0038] Figure 10 It is K x Na 0.67-x Cu 0.1 Ni 0.3 Mn 0.6 Cyclic performance diagram of O2 series layered oxide cathode active materials.

[0039] Figure 11 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 SEM image of O2 after one month of exposure to air.

[0040] Figure 12 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 SEM image of O2 exposure in aquatic environments.

[0041] Figure 13 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6SEM image of O2 after 100 cycles at a current density of 0.1 Ag⁻¹.

[0042] Figure 14 Na obtained in Comparative Example 1 0.67 Cu 0.1 Ni 0.3 Mn 0.6 SEM image of O2. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] Preparation of the positive electrode active material: Potassium carbonate (K2CO3), sodium carbonate (Na2CO3), copper acetate (Cu(CH3COO)2·H2O), nickel acetate (Ni(CH3COO)2·4H2O), and manganese acetate (Mn(CH3COO)2·4H2O) were dissolved in an appropriate amount of deionized water in a molar ratio of K2CO3:Na2CO3:Cu(CH3COO)2·H2O:Ni(CH3COO)2·H2O:Mn(CH3COO)2·H2O = 0.025:0.31:0.1:0.3:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100% to 105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5℃ for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The heating rate was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide K was obtained. 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 O2.

[0046] The resulting layered sodium intercalated transition metal oxide K 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0047] Example 2

[0048] Preparation of the positive electrode active material: Potassium carbonate (K2CO3), sodium carbonate (Na2CO3), copper acetate (Cu(CH3COO)2·H2O), nickel acetate (Ni(CH3COO)2·4H2O), and manganese acetate (Mn(CH3COO)2·4H2O) were dissolved in an appropriate amount of deionized water in a molar ratio of K2CO3:Na2CO3:Cu(CH3COO)2·H2O:Ni(CH3COO)2·H2O:Mn(CH3COO)2·H2O = 0.05:0.285:0.1:0.3:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100% to 105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5℃ for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The heating rate was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide K was obtained. 0.1 Na 0.57 Cu 0.1 Ni 0.3 Mn 0.6 O2.

[0049] The resulting layered sodium intercalated transition metal oxide K 0.1 Na 0.57 Cu 0.1 Ni 0.3 Mn 0.6 O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0050] Example 3

[0051] Preparation of the positive electrode active material: Potassium carbonate (K2CO3), sodium carbonate (Na2CO3), copper acetate (Cu(CH3COO)2·H2O), nickel acetate (Ni(CH3COO)2·4H2O), and manganese acetate (Mn(CH3COO)2·4H2O) were dissolved in an appropriate amount of deionized water in a molar ratio of K2CO3:Na2CO3:Cu(CH3COO)2·H2O:Ni(CH3COO)2·H2O:Mn(CH3COO)2·H2O = 0.075:0.26:0.1:0.3:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100% to 105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5℃ for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The heating rate was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide K was obtained. 0.15 Na 0.52 Cu 0.1 Ni 0.3 Mn 0.6 O2.

[0052] The resulting layered sodium intercalated transition metal oxide K 0.15 Na 0.52 Cu 0.1 Ni 0.3 Mn 0.6 O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0053] Example 4

[0054] Preparation of the positive electrode active material: Potassium carbonate (K2CO3), sodium carbonate (Na2CO3), copper acetate (Cu(CH3COO)2·H2O), nickel acetate (Ni(CH3COO)2·4H2O), and manganese acetate (Mn(CH3COO)2·4H2O) were dissolved in an appropriate amount of deionized water in a molar ratio of K2CO3:Na2CO3:Cu(CH3COO)2·H2O:Ni(CH3COO)2·H2O:Mn(CH3COO)2·H2O = 0.1:0.235:0.1:0.3:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100-105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5℃ for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The heating rate was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide K was obtained. 0.2 Na 0.47 Cu 0.1 Ni 0.3 Mn 0.6 O2.

[0055] The resulting layered sodium intercalated transition metal oxide K 0.2 Na 0.47 Cu 0.1 Ni 0.3 Mn 0.6 O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0056] Example 5

[0057] Preparation of the positive electrode active material: Potassium carbonate (K2CO3), sodium carbonate (Na2CO3), copper acetate (Cu(CH3COO)2·H2O), nickel acetate (Ni(CH3COO)2·4H2O), and manganese acetate (Mn(CH3COO)2·4H2O) were dissolved in an appropriate amount of deionized water in a molar ratio of K2CO3:Na2CO3:Cu(CH3COO)2·H2O:Ni(CH3COO)2·H2O:Mn(CH3COO)2·H2O = 0.15:0.185:0.1:0.3:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100-105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5℃ for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The heating rate was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide K was obtained. 0.3 Na 0.37 Cu 0.1 Ni 0.3 Mn 0.6 O2.

[0058] The resulting layered sodium intercalated transition metal oxide K 0.3 Na 0.37 Cu 0.1 Ni 0.3 Mn 0.6 O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0059] Comparative Example 1

[0060] Sodium carbonate (Na₂CO₃), copper acetate (Cu(CH₃COO)₂·H₂O), nickel acetate (Ni(CH₃COO)₂·4H₂O), and manganese acetate (Mn(CH₃COO)₂·4H₂O) were dissolved in an appropriate amount of deionized water at a molar ratio of Na₂CO₃:Cu(CH₃COO)₂·H₂O:Ni(CH₃COO)₂·H₂O:Mn(CH₃COO)₂·H₂O = 0.335:0.1:0.3:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100-105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5°C for 1 minute.-1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 1 minute. -1 The temperature was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide Na was obtained. 0.67 Cu 0.1 Ni 0.3 Mn 0.6 O2.

[0061] The resulting layered sodium intercalated transition metal oxide Na 0.67 Cu 0.1 Ni 0.3 Mn 0.6 O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0062] Comparative Example 2

[0063] Sodium carbonate (Na₂CO₃), ferric nitrate (Fe(NO₃)₃·9H₂O), nickel acetate (Ni(CH₃COO)₂·4H₂O), and manganese acetate (Mn(CH₃COO)₂·4H₂O) were dissolved in an appropriate amount of deionized water at a molar ratio of Na₂CO₃:Fe(NO₃)₃·9H₂O:Ni(CH₃COO)₂·H₂O:Mn(CH₃COO)₂·H₂O = 0.335:0.1:0.3:0.6. The actual mass of the sodium source in the mixed raw materials was controlled within 100-105% of the theoretical mass to avoid sodium ion loss during the high-temperature phase formation process. After evaporating all the water from the solution, the resulting solid precursor sample was in air at 5°C for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The temperature was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide Na was obtained. 0.67 Fe 0.1 Ni 0.3 Mn 0.6 O2.

[0064] The resulting layered sodium intercalated transition metal oxide Na 0.67 Fe 0.1 Ni 0.3 Mn 0.6 O2 is ground into particles with an average particle size Dv 50 refers to particles ranging from 0.5 to 10 μm.

[0065] Comparative Example 3

[0066] Sodium carbonate (Na₂CO₃), nickel acetate (Ni(CH₃COO)₂·4H₂O), and manganese acetate (Mn(CH₃COO)₂·4H₂O) were dissolved in an appropriate amount of deionized water at a molar ratio of Na₂CO₃:Ni(CH₃COO)₂·H₂O:Mn(CH₃COO)₂·H₂O = 0.335:0.4:0.6. The actual mass of sodium source in the mixed raw materials could be controlled within 100-105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5°C for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1 The temperature was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide Na was obtained. 0.67 Ni 0.4 Mn 0.6 O2.

[0067] The resulting layered sodium intercalated transition metal oxide Na 0.67 Ni 0.4 Mn 0.6 O2 is ground into particles with an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0068] Comparative Example 4

[0069] Sodium carbonate (Na₂CO₃) and manganese acetate (Mn(CH₃COO)₂·4H₂O) were dissolved in an appropriate amount of deionized water at a molar ratio of Na₂CO₃:Mn(CH₃COO)₂·H₂O = 0.335:1. The actual mass of the sodium source in the mixed raw material was controlled within 100-105% of the theoretical mass to avoid the loss of sodium ions during the high-temperature phase formation process. After evaporating all the water in the solution, the resulting solid precursor sample was in air at 5°C for 1 minute. -1 The initial heating rate was increased to 400℃ and held for 10 hours to remove all organic components. After cooling, the resulting powder sample was ground into a fine powder and then pressed into tablets using a tablet press. The resulting sample was then placed in air at 5℃ for 5 minutes. -1The temperature was increased to 900℃ for a second time and held for 10 hours. After natural cooling, layered sodium intercalated transition metal oxide Na was obtained. 0.67 MnO2.

[0070] The resulting layered sodium intercalated transition metal oxide Na 0.67 MnO2 is ground to an average particle size D v 50 refers to particles ranging from 0.5 to 10 μm.

[0071] Electrochemical performance testing:

[0072] Battery Assembly: The sodium-ion battery transition metal oxide positive electrode active materials obtained in Examples 1-5 and Comparative Examples 1-4 were used as active materials. They were mixed at a mass ratio of active material: acetylene black: polyvinylidene fluoride (PVDF) of 8:1:1, and an appropriate amount of N-methylpyrrolidone was added to form a viscous slurry. This slurry was coated onto a rough aluminum foil and baked in a vacuum drying oven at 80°C for 8 hours. After complete drying, the entire electrode sheet was shaped into appropriately sized circular electrodes using a die-cutting machine. Using metallic sodium as the counter electrode, glass fiber as the separator, and 1 mol / L NaClO4 (EC and DEC in a 1:1 solvent volume ratio) as the electrolyte, 2016 coin cells were assembled in an argon-protected glove box. The batteries were tested within a voltage range of 2.0–4.0 V, with 1C = 170 mAg. -1 The electrochemical cycling performance was tested at 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C, and the results are shown in Table 1.

[0073] Table 1 Based on Na 0.67 Mn 0.6 Ni 0.3 Cu 0.1 Crystal parameters after XRD refinement of O2 sample

[0074]

[0075] Table 2 is based on K 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1 Crystal parameters after XRD refinement of O2 sample

[0076]

[0077] Table 3 Electrochemical performance tests of sodium-ion battery transition metal oxide cathode active materials obtained in Examples 1-5 and Comparative Examples 1-4

[0078]

[0079] Figure 1 Na in Comparative Example 1 0.67 Mn 0.6 Ni 0.3 Cu 0.1 The XRD pattern of O2 shows that the sample without alkali metal doping belongs to the P2 type layered oxide structure, which is a hexagonal close packing with a space group of P63 / mmc. The corresponding refinement error values ​​are Rp<10% and Rwp<15%, indicating that the calculated refinement results are true and reliable.

[0080] Figure 2 K in Example 1 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1 The O2 refinement image shows that the sample doped with alkali metal K belongs to the P2 type layered oxide structure, which is a hexagonal close packing with a space group of P63 / mmc. The refinement error values ​​are Rp<10% and Rwp<15%, indicating that the calculated refinement results are true and reliable. In addition, the refinement results show that the doping of alkali metal did not change the crystal form of the material.

[0081] Figure 3 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 SEM image of O2, from Figure 1 It can be seen that the material produced by this invention method exhibits obvious layered stacking structural characteristics.

[0082] Figure 4 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 TEM image of O2; the material produced by this invention appears as a sheet-like material with clearly defined edges.

[0083] Figure 5 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 STEM image of O2 (marking the corresponding (101) crystal planes, with the measured lattice spacing d = 0.243 nm).

[0084] Figure 6 K obtained in Example 1 0.05 Na 0.62 Cu0.1 Ni 0.3 Mn 0.6 STEM image of O2 (marking the corresponding (002) crystal plane, with a measured lattice spacing d = 0.564 nm), where the distance of the (002) crystal plane corresponds to the interlayer spacing along the c-axis. In this invention, the lattice spacing corresponding to the (002) crystal plane of the sample after alkali metal site doping is greater than the lattice spacing of the XRD standard card (PDF#70-3726), which indicates that K ions have been successfully doped into the crystal structure and have expanded the interlayer spacing along the c-axis.

[0085] Figure 7 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 The EDS mapping of O2 shows that K, Na, Mn, Ni, Cu, and O elements are uniformly distributed on the surface of the sample particles prepared in this invention, which indicates that this invention method is a suitable method for preparing a uniform layered oxide.

[0086] Figure 8 It is K x Na 0.67-x Cu 0.1 Ni 0.3 Mn 0.6 The rate performance diagram of O2 series layered oxide cathode active materials shows that the series of samples prepared by this invention method all have excellent rate performance.

[0087] Figure 9 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 O2 in 1Ag -1 Long-term cycling stability under high current density.

[0088] Figure 10 It is K x Na 0.67-x Cu 0.1 Ni 0.3 Mn 0.6 Cyclic performance diagram of O2 series layered oxide cathode active materials.

[0089] Figure 11 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6SEM image of the sample after one month of O2 exposure to air. The image shows that the sample still maintains a good layered structure after one month of exposure to air, demonstrating excellent air stability.

[0090] Figure 12 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 SEM images of O2 exposed to an aquatic environment show that some slippage occurred between the layered oxide stacks of the sample after water treatment, but the overall layered structure was still well maintained, demonstrating excellent water stability.

[0091] Figure 13 K obtained in Example 1 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 O2 in 0.1Ag -1 The SEM image after 100 cycles at the current density clearly shows the interface between the activated carbon and the layered oxide. After 100 electrochemical cycles, the sodium-ion battery oxide material prepared by this invention still maintains a good layered structure, exhibiting excellent structural stability.

[0092] Figure 14 Na obtained in Comparative Example 1 0.67 Cu 0.1 Ni 0.3 Mn 0.6 The SEM images of O2 show that the undoped samples do not exhibit clear edges and layered structures, indicating that the larger interlayer spacing in the c-axis direction after alkali metal doping is conducive to the formation of layered oxides.

[0093] Table 1 shows Na 0.67 Mn 0.6 Ni 0.3 Cu 0.1 The lattice parameters corresponding to the refined XRD results of O2, and the site occupancy results of the refined metal ions, show that transition metals Mn, Ni, and Cu occupy the same site, while Na ions occupy two different sites. f and Na e The ratio is 0.35:0.32.

[0094] Table 2 shows K 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1The lattice parameters corresponding to the XRD refinement results of O2, and

[0095] Na 0.67 Mn 0.6 Ni 0.3 Cu 0.1 The XRD refinement results for O2 are consistent, with transition metals Mn, Ni, and Cu occupying the same site, while Na ions occupy two different sites. f and Na e Among them, K ions occupy the Na+ ions. e Site. Additionally, comparison.

[0096] K 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1 O2 and Na 0.67 Mn 0.6 Ni 0.3 Cu 0.1 The results of the O2 refinement show that K after K doping... 0.05 Na 0.62 Mn 0.6 Ni 0.3 Cu 0.1 The unit cell parameters a, b, and c of the O2 sample are all greater than those of the undoped Na sample. 0.67 Mn 0.6 Ni 0.3 Cu 0.1 O2 sample.

[0097] Table 3 shows the electrochemical performance tests of the sodium-ion battery transition metal oxide cathode active materials obtained in Examples 1-5 and Comparative Examples 1-4.

[0098] Comparative analysis of Example 1 and Comparative Example 1 shows that the K-doped sample exhibits a higher electrochemical capacity. This indicates that the larger interlayer spacing and regular layered stacking morphology after K doping are beneficial to the storage and transport of sodium ions, thus providing a higher capacity.

[0099] Comparative analysis of Examples 1-5 shows that the charge / discharge capacity of the material decreases with increasing K doping content. This may be because the doping of larger inert K ions into the crystal structure reduces the electrochemical capacity of the material and even hinders the transport of sodium ions, leading to a decrease in capacity.

[0100] Comparative analysis of Examples 1-5 shows that the 1C capacity retention rate of the materials described in Examples 1-5 of this invention is maintained in the range of 97.2-100%, the air stability is maintained in the range of 98.8-100%, the water stability is maintained in the range of 98.2-100%, and the average coulombic efficiency is maintained in the range of 100% ± 0.5. This indicates that the series of layered oxide materials described in this invention all exhibit excellent structural stability, cycle stability, and air and water stability.

[0101] Comparative analysis of samples 1-3 shows that the electrode materials prepared by the method of this invention without K-ion doping all exhibit lower initial electrochemical capacity, as well as lower cycle stability, water and air stability, especially sample 3, which shows lower stability in Na+. 0.67 The electrode material of the (Mn-Ni-Fe)O2 system exhibited short circuits under high current 1C cycling, demonstrating poor performance and even worse stability in water and air. This may be because divalent Fe ions are unstable in water and air environments and are easily oxidized, resulting in the instability of the electrode material.

[0102] Comparative analysis of Example 1 and Comparative Example 4 shows that the electrode material of Comparative Example 4 exhibits a higher initial electrochemical capacity. This is due to the increased Mn content, which allows Mn to undergo oxidation during the electrochemical process. 2+ / Mn 3+ The conversion of Mn ions transfers two electrons, resulting in a higher initial capacity. However, compared to Example 1, Comparative Example 4 exhibits worse stability. This is due to the Jameer-Taylor effect of Mn ions in the electrochemical reaction, which leads to structural instability and thus instability in electrochemical performance, resulting in rapid capacity decay and poor stability to water and air.

[0103] The above content is only a specific implementation example of the present invention, and not all application examples of the present invention. All schemes that follow the technical concept of the present invention or make modifications based on the technical concept of the present invention are within the protection scope of the claims of the present invention.

Claims

1. A high-stability layered-oxide sodium-ion battery cathode active material, characterized in that, The positive electrode active material has a chemical formula of K 0.05 Na 0.62 Cu 0.1 Ni 0.3 Mn 0.6 O2; The positive electrode active material has a layered stack structure in microcosm.

2. The high-stability layered-oxide sodium-ion battery cathode active material of claim 1, wherein, The crystal structure of the positive electrode active material is a P2-type structure, having two sites of sodium ions, i.e., Na e and Na f , with a ratio of the number of sodium ions of Na e : Na f = 0.32:0.

35.

3. The high-stability layered-oxide sodium-ion battery cathode active material of claim 1, wherein, The crystal structure of the positive electrode active material has hexagonal closest packing, space group P63 / mmc.

4. The high-stability layered-oxide sodium-ion battery cathode active material of claim 3, wherein, The x-ray diffraction of the positive electrode active material contains characteristic peaks of (100) crystal face and (002) crystal face.

5. The highly stable layered-oxide sodium-ion battery cathode active material of claim 1, wherein, The average particle diameter D of the positive electrode active material is preferably 0.5 to 10 μm. v 50 is 0.5 to 10 μm.

6. The highly stable layered-oxide sodium-ion battery cathode active material of claim 1, wherein, After the positive electrode active material is exposed to air for more than one month, the attenuation of the electrochemical capacity is less than 5% compared with the positive electrode active material not exposed to air.

7. The highly stable layered-oxide sodium-ion battery cathode active material of claim 1, wherein, After the positive electrode active material is exposed to a water environment for more than 24 hours, the attenuation of the electrochemical capacity is less than 5% compared with the positive electrode active material not exposed to the water environment.

8. A method for preparing the high-stability layered-oxide sodium-ion battery cathode active material according to any one of claims 1-7, characterized in that, The method comprises the following steps: (1) A mixed salt solution is prepared by mixing potassium salt, sodium salt, manganese salt, nickel salt and copper salt in a certain proportion, citric acid is added and dissolved in water, and then the solution is hydrothermally evaporated to dryness to obtain a sol-gel, the obtained gel is dried and ground to obtain a solid powder; (2) The solid powder obtained in step (1) is subjected to first-stage temperature rising calcination in an air atmosphere, the first-stage temperature rising calcination removes the organic components in the precursor, and after the temperature drops to room temperature, the obtained sample is ground into a uniform powder; (3) The uniform powder obtained in step (2) is pressed into a tablet, and then the tablet-shaped sample is subjected to second-stage temperature rising calcination in an air atmosphere, and after the temperature drops to room temperature, the block-shaped sample is ground into a powder again to obtain the high-stability layered oxide sodium ion battery positive electrode active material.

9. The method of claim 8, wherein the method is characterized by: The first temperature rising calcination is carried out at a temperature rising rate of 5°C / min in a muffle furnace to a temperature of 300-400°C, and the temperature is maintained for 6-12 hours. -1 The second temperature rising calcination is carried out at a temperature rising rate of 5°C / min in a muffle furnace to a temperature of 600-700°C, and the temperature is maintained for 6-12 hours. The conditions for the second stage of heating and calcination are as follows: the powder is heated in a muffle furnace at 5°C for 1 minute. -1 The heating rate is increased to 400-900℃, and the temperature is maintained for 6-12 hours; The temperature of the second-stage temperature rising calcination is higher than that of the first-stage temperature rising calcination, and rising to a higher temperature is conducive to phase formation.

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