A Li + Doped p2-type layered oxide sodium-ion battery cathode material and method of making

Abstract

The application discloses a kind of Li + The application discloses a P2-type layered oxide sodium-ion battery positive electrode material and a preparation method thereof, and belongs to the technical field of sodium-ion battery materials. + The stable layered crystal framework is constructed by doping, and the material microstructure is optimized by combining a urea chelation hydrothermal method with a gradient high-temperature solid-phase sintering process. + The P2-O2 irreversible phase transition under high voltage is effectively inhibited by means of the "support effect" of Li The sodium-ion transmission path is shortened, and the electrode / electrolyte interface contact efficiency is improved, so that the cycle stability and interface kinetics performance of the material are simultaneously improved.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and relates to sodium-ion battery cathode materials and their preparation methods, specifically involving a Li... + P2-doped layered oxide cathode material for sodium-ion batteries and its preparation method. Background Technology

[0002] With the accelerated transformation of the global energy structure, lithium-ion batteries have become the mainstream choice for energy storage and power batteries. However, lithium resources are scarce in the earth's crust and unevenly distributed geographically, which has led to a continuous increase in the cost of raw materials for lithium-ion batteries, limiting their promotion and application in the field of large-scale energy storage.

[0003] Sodium-ion batteries have become an ideal alternative technology for large-scale energy storage systems and low-speed power batteries due to their advantages such as abundant sodium resources, low raw material costs, and high electrochemical safety. Among the cathode materials of sodium-ion batteries, P2-type layered transition metal oxides (general formula NaxTMO2) exhibit excellent electrochemical kinetic characteristics due to their open sodium-ion diffusion channels and high theoretical specific capacity, making them an important research direction for cathode materials.

[0004] However, P2-type layered oxide cathode materials face significant technical bottlenecks in practical applications: during deep charge-discharge processes, especially in the high-voltage range of 2.0-4.2V, the material is prone to irreversible P2-O2 phase transitions, leading to lattice distortion, layered structure collapse, and consequently, rapid capacity decay. This is accompanied by deterioration of interfacial dynamics and a significant increase in charge transfer resistance. Existing modification methods for this problem are often complex, costly, and have limited modification effects, failing to meet the demands of industrial production. Therefore, there is an urgent need to develop a simple, efficient, and low-cost modification strategy for P2-type layered oxides. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a Li + P2-doped layered oxide cathode material for sodium-ion batteries and its preparation method, using Li + Doping stabilizes the layered framework, effectively suppressing the irreversible P2-O2 phase transition under high voltage. It also optimizes the microstructure of the material, improves its overall electrochemical performance, and achieves synergistic improvement in cycle stability, interfacial kinetics, and rate performance. Furthermore, the preparation process is simple and controllable, making it suitable for large-scale industrial production.

[0006] This invention is achieved through the following technical solution: A Li + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material includes the following steps: Step 1: Dissolve MnSO4·H2O and FeSO4·H2O in deionized water at an equimolar ratio to form a mixed solution with a transition metal ion concentration of 0.8~1.2 mol / L. Add urea to the mixed solution at a urea to transition metal ion molar ratio of (3~5):1, and stir until evenly dispersed. Transfer the solution to a hydrothermal reactor and react at 150~170℃ for 10~14 h. After cooling, filter, wash, and dry to obtain MnSO4·H2O. 0.5 Fe 0.5 CO3 precursor; Step 2, press Mn 0.5 Fe 0.5 The stoichiometric ratio of CO3 precursor, NaOH powder, and LiOH powder is 1:(0.55~0.70):(0.03~0.07). The raw materials are ground until uniformly mixed to obtain a mixed powder. The mixed powder is placed in a tube furnace and heated to 430~470℃ in air atmosphere for 4~6 h, then heated to 880~920℃ and held for 10~14 h. After natural cooling, Li is obtained. + P2-doped layered oxide sodium-ion battery cathode material.

[0007] The present invention also has the following technical features: Preferably, the stirring in step one is carried out at 20~30℃ for 4~6 hours.

[0008] Preferably, the washing in step one involves alternating between deionized water and anhydrous ethanol for 3 to 5 times each.

[0009] Preferably, the drying in step one is vacuum drying at 50~70℃ for 10~14 h.

[0010] Preferably, the grinding and mixing time in step two is 30~60 min, and the particle size of the mixed powder is ≤50μm.

[0011] Preferably, the heating rate of the tubular furnace in step two is 2~4℃ / min.

[0012] This invention also protects a Li prepared according to the above method. + P2-type layered oxide sodium-ion battery cathode material with stoichiometric formula Na x Li y Mn 0.5 Fe 0.5 CO3O2, where x = 0.55~0.70 and y = 0.03~0.07.

[0013] Furthermore, the Li of the present invention +The doped P2-type layered oxide sodium-ion battery cathode material has a hexagonal P2-type crystal structure with space group P63 / mmc and lattice parameters a=4.75~4.83 Å, b=4.75~4.83 Å, c=15.5~15.8 Å. It exhibits a secondary spherical particle morphology with a particle size of 3~20 μm.

[0014] Compared with the prior art, the present invention has the following significant advantages: This invention utilizes precise Li + Doping stabilizes the layered framework of P2-type layered oxides, Li + The stable Li-O covalent bond formed with O generates a "pillar effect," which can effectively suppress the irreversible P2-O2 phase transition under high voltage, alleviate lattice distortion and structural collapse during cycling, and significantly improve the cycling stability of the material. The resulting material exhibits excellent cycling stability at 100 mA·g. -1 The capacity retention rate can reach 86.1% after 100 cycles at current density; This invention employs a urea chelation-assisted hydrothermal method to prepare the precursor, achieving a uniform distribution of Mn and Fe transition metal ions. After subsequent high-temperature sintering, the material retains a secondary spherical particle morphology of 5-15 μm. This morphology not only increases the contact area between the electrode and the electrolyte but also shortens the sodium ion transport path, effectively optimizing the interfacial kinetics of the material. This results in a charge transfer resistance as low as 66.0 Ω and a significantly improved rate performance at 500 mA·g. -1 It still exhibits high discharge specific capacity under high current density; The preparation process of this invention is simple and controllable, requiring no complex production equipment. The raw materials used, such as MnSO4·H2O, FeSO4·H2O, NaOH, and LiOH, are all common industrial raw materials, which are low in cost and environmentally friendly. The process parameters of gradient high-temperature sintering are easy to control industrially, making it suitable for large-scale industrial production and showing good prospects for industrial application.

[0015] The Li obtained in this invention + The doped P2-type layered oxide cathode material has a pure hexagonal P2-type crystal structure with no impurity phase formation, and Li + The electrochemical structure reversibility of the doped material is greatly improved, the redox peak potential difference is small and the peak shape is stable. Combined with the optimized microstructure, the cycle stability, interfacial kinetics performance and rate performance are synergistically improved. The material has excellent comprehensive electrochemical performance and can be widely used in sodium-ion battery applications such as large-scale energy storage and low-speed power batteries. Attached Figure Description

[0016] Figure 1 The XRD patterns of the cathode materials in Example 1 and Comparative Example 1 are shown below. Figure 2 For Fe0.5 Mn 0.5 SEM images of CO3 precursors (4 μm and 400 nm scale). Figure 3 SEM images (4 μm scale and 400 nm scale) of the cathode materials of Example 1 and Comparative Example 1. Figure 4 Cyclic performance curves (100 mA·g) of the cathode materials in Example 1 and Comparative Example 1 -1 ); Figure 5 Rate performance curves (20-500 mA·g) of the cathode materials in Example 1 and Comparative Example 1 -1 ); Figure 6 EIS spectra and equivalent circuits of the cathode materials in Example 1 and Comparative Example 1; Figure 7 XPS spectra of the cathode material in Example 1 (Na 1s, Fe 2p, Li 1s, Mn 2p); Figure 8 The image shows the SEM-EDS energy dispersive spectroscopy (EDS) spectrum of the cathode material in Example 1. Figure 9 For Fe 0.5 Mn 0.5 Thermogravimetric analysis curves of CO3 precursor and NaOH; Figure 10 Cyclic voltammetry curves (1.5-4.5 V) of the cathode materials in Example 1 and Comparative Example 1. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0018] Example 1 Step 1: Weigh 50 mmol MnSO4·H2O (8.45 g) and 50 mmol FeSO4·H2O (8.375 g), dissolve them in 100 mL deionized water; add 400 mmol urea (24.024 g), stir at 25 ℃ for 5 h; transfer to a 100 mL hydrothermal reactor, react at 160 ℃ for 12 h; after cooling, filter, wash alternately with deionized water and anhydrous ethanol 3 times each, and dry under vacuum at 60 ℃ for 12 h to obtain Mn 0.5 Fe 0.5 CO3 precursor; Step 2: Weigh 50 mmol Mn 0.5 Fe 0.5CO3 precursor (7.15 g), 31 mmol NaOH (1.24 g), and 2.5 mmol LiOH (0.0598 g) were ground for 30 min until homogeneous, yielding a mixed powder with a particle size ≤50 μm. The powder was then placed in a tube furnace and heated to 450 °C at a rate of 3 °C / min under air atmosphere, held for 5 h, and then heated to 900 °C and held for 12 h. After cooling, Na₂O₃ was obtained. 0.62 Li 0.05 Mn 0.5 Fe 0.5 O2 sodium-ion battery cathode material.

[0019] Na prepared using the present invention 0.62 Li 0.05 Mn 0.5 Fe 0.5 O2 sodium-ion battery cathode material is used in the assembly of sodium-ion batteries, and the specific operation is as follows: Positive electrode preparation: The positive electrode material, acetylene black and polyvinylidene fluoride were mixed at a weight ratio of 7:2:1. N-methylpyrrolidone was added to prepare a slurry (polyvinylidene fluoride concentration 0.2 g / mL). The slurry was ultrasonically treated for 3 min. It was then coated onto an aluminum foil current collector, vacuum dried at 60℃ for 12 h, rolled at 10 MPa pressure for 5 min, and cut into positive electrode sheets with a diameter of 12 mm.

[0020] Battery assembly: In an argon glove box (H2O, O2≤0.01 ppm), button cells were assembled using metallic sodium as the negative electrode, Whatman GF / D as the separator, and 1 mol / L NaPF6 (EC:DMC:EMC=1:1:1) as the electrolyte, and allowed to stand for 12 h.

[0021] Performance testing: at 20mA·g - ¹Activation was achieved by cycling the current density for 3 cycles within the voltage range of 2.0–4.2 V and at a current density of 100 mA·g. - ¹Cycling performance was tested at current density, and the capacity retention rate was 86.1% after 100 cycles.

[0022] Example 2 Step 1: Weigh 50 mmol MnSO4·H2O (8.45 g) and 50 mmol FeSO4·H2O (8.375 g), dissolve them in 100 mL deionized water; add 300 mmol urea (18.018 g), stir at 20℃ for 6 h; transfer to a 100 mL hydrothermal reactor, react at 150℃ for 14 h; after cooling, filter, wash alternately with deionized water and anhydrous ethanol 4 times each, and vacuum dry at 50℃ for 14 h to obtain Mn 0.5 Fe 0.5 CO3 precursor; Step 2: Weigh 50 mmol Mn 0.5 Fe 0.5 CO3 precursor (7.15 g), 27.5 mmol NaOH (1.10 g), and 1.5 mmol LiOH (0.0359 g) were ground for 50 min until homogeneous, yielding a mixed powder with a particle size ≤50 μm. The powder was then placed in a tube furnace and heated to 430 °C at a rate of 2 °C / min under air atmosphere, held for 6 h, and then further heated to 880 °C and held for 14 h. After cooling, Na₂O₃ was obtained. 0.55 Li 0.03 Mn 0.5 Fe 0.5 O2 sodium-ion battery cathode material.

[0023] Na prepared using the present invention 0.55 Li 0.03 Mn 0.5 Fe 0.5 The O2 sodium-ion battery cathode material is used to assemble sodium-ion batteries, with a capacity retention of 85.7% after 100 cycles and a charge transfer resistance of 68.3Ω.

[0024] Example 3 Step 1: Weigh 50 mmol MnSO4·H2O (8.45 g) and 50 mmol FeSO4·H2O (8.375 g), dissolve them in 100 mL deionized water; add 500 mmol urea (30.03 g), stir at 30℃ for 4 h; transfer to a 100 mL hydrothermal reactor, react at 170℃ for 10 h; after cooling, filter, wash alternately with deionized water and anhydrous ethanol 5 times each, and vacuum dry at 70℃ for 10 h to obtain Mn 0.5 Fe 0.5 CO3 precursor; Step 2: Weigh 50 mmol Mn 0.5 Fe 0.5 CO3 precursor (7.15 g), 35 mmol NaOH (1.40 g), and 3.5 mmol LiOH (0.0838 g) were ground for 60 min until homogeneous, yielding a mixed powder with a particle size ≤50 μm. The powder was then placed in a tube furnace and heated to 470 °C at a rate of 4 °C / min under air atmosphere, held for 4 h, and then further heated to 920 °C and held for 10 h. After cooling, Na₂O₃ was obtained. 0.70 Li 0.05 Mn 0.5 Fe 0.5 O2 sodium-ion battery cathode material.

[0025] Na prepared using the present invention 0.70 Li 0.07 Mn 0.5 Fe0.5 O2 sodium-ion battery cathode material is used to assemble sodium-ion batteries, with a capacity retention of 86.3% after 100 cycles and a capacity of 500 mA·g. -1 The specific capacity at the lower discharge level is 36.1 mAh·g. -1 .

[0026] Comparative Example 1 The difference from Example 1 is that LiOH was not added in step two, while the other preparation conditions were the same, resulting in undoped Na. 0.67 Mn 0.5 Fe 0.5 The O2 cathode material retains 56.1% of its capacity after 100 cycles and has a charge transfer resistance of 407.6 Ω.

[0027] Comparative Example 2 The difference from Example 1 is that the pre-sintering temperature in step two is 400°C, while the other preparation conditions are the same. The XRD pattern of the obtained cathode material shows a small number of impurity peaks, and the capacity retention rate after 100 cycles is 72.3%.

[0028] Comparative Example 3 The difference from Example 1 is that the high-temperature sintering temperature in step two is 850°C, while the other preparation conditions are the same. The resulting cathode material has insufficient crystallinity, and the capacity retention rate after 100 cycles is 68.5%.

[0029] Performance testing Crystal structure characterization: The crystal structure was characterized using a Bruker D8-ADVANCE X-ray diffractometer (Cu-Kα rays, λ=1.5406Å), with 2θ=10-80° and a scan rate of 2° / min. The results showed that the materials in Examples 1-3 had a pure P2 type structure with no O2 phase impurity peaks; the materials in Comparative Examples 1-3 had impurity peaks or crystallinity defects. Figure 1 The XRD patterns of the cathode materials in Example 1 and Comparative Example 1 are shown below; Figure 1 As shown, the diffraction peaks of Example 1 completely match the standard card PDF#27-0751, with no impurity peaks, indicating a pure P2 type structure; after cycling, Comparative Example 1 shows characteristic peaks of the O2 phase (around 2θ=35°), proving that an irreversible phase transition has occurred.

[0030] Microscopic morphology characterization: Observation using a Hitachi Regulus 8010 scanning electron microscope (Japan) showed that the materials in Examples 1-3 were secondary spherical particles with a particle size of 5-15 μm and a rough surface; the material in Comparative Example 1 showed obvious particle agglomeration. Figure 2 For Fe 0.5 Mn 0.5 SEM images of CO3 precursors (4 μm and 400 nm scales); such as Figure 2As shown, Fe 0.5 Mn 0.5 The CO3 precursor is a secondary spherical particle formed by the aggregation of primary nanoparticles, with a dense surface and uniform particle size.

[0031] Figure 3 SEM images (4 μm and 400 nm scales) of the cathode materials in Example 1 and Comparative Example 1; as shown Figure 3 As shown, the material in Example 1 retains a secondary spherical morphology, has a rough surface, and a large specific surface area; the material in Comparative Example 1 has agglomerated particles and an irregular morphology.

[0032] Electrochemical performance testing: Cyclic performance: at 100 mA·g -1 At current densities, the capacity retention rate of Examples 1-3 after 100 cycles was 85.7%-86.3%; that of Comparative Examples 1-3 was 56.1%-72.3%. Figure 4 Cyclic performance curves (100 mA·g) of the cathode materials in Example 1 and Comparative Example 1. -1 );like Figure 4 As shown, Example 1 exhibits slow capacity decay, with a capacity retention rate of 86.1% after 100 cycles; Comparative Example 1 shows rapid capacity decay, with a retention rate of only 56.1%.

[0033] Rate performance: at 500 mA·g -1 At the given current density, the discharge specific capacity of Examples 1-3 is 35.2-36.1 mA·h·g. -1 It is much higher than the 10.8 mA·h·g of Comparative Example 1. -1 . Figure 5 Rate performance curves (20-500 mA·g) of the cathode materials in Example 1 and Comparative Example 1 -1 );like Figure 5 As shown, the discharge specific capacity of Example 1 at all current densities is higher than that of Comparative Example 1 at 500 mA·g. -1 It remains at 35.2 mA·h·g -1 .

[0034] Impedance testing: Tested using a Shanghai Chenhua CHI-660F electrochemical workstation (frequency 0.1-100000Hz). The charge transfer resistance of Examples 1-3 was 66.0-68.3 Ω, which was significantly lower than the 407.6 Ω of Comparative Example 1. Figure 6 EIS spectra and equivalent circuits of the cathode materials in Example 1 and Comparative Example 1; Figure 6 As shown, the charge transfer resistance (Rct=66.0Ω) of Example 1 is much lower than that of Comparative Example 1 (Rct=407.6Ω), indicating that the interface dynamics are superior.

[0035] Figure 7XPS spectra of the cathode material in Example 1 (Na 1s, Fe 2p, Li 1s, Mn 2p); as shown Figure 7 As shown, the Na 1s binding energy is approximately 1074.58 eV, Fe 2p corresponds to +3 valence, Li 1s binding energy is approximately 60.02 eV, and Mn 2p shows Mn 3+ and Mn 4+ Coexistence, proving Li + Successful doping and the element valence state conforms to the design.

[0036] Figure 8 The image shows the SEM-EDS energy dispersive spectroscopy (EDS) spectrum of the cathode material in Example 1; as shown. Figure 8 As shown, Na, Mn, and Fe elements are uniformly distributed, proving that Na 0.62 Li 0.05 Mn 0.5 Fe 0.5 O2 synthesis was successful.

[0037] Figure 9 For Fe 0.5 Mn 0.5 Thermogravimetric analysis curves of CO3 precursor and NaOH; such as Figure 9 As shown, the weight loss is 7.66% (evaporation of water of crystallization) in the 35-245℃ range and 25.58% (decomposition of carbonates) in the 245-850℃ range, providing a basis for the sintering process.

[0038] Cyclic voltammetry test: scan voltage 1.5-4.5 V, scan rate 0.1 mV·s -1 The redox peak potential difference in Examples 1-3 is small and the peak shape is stable, while the peak shape shift in Comparative Example 1 is obvious. Figure 10 The cyclic voltammetry curves (1.5-4.5 V) for the cathode materials of Example 1 and Comparative Example 1 are shown. Figure 10 As shown, the redox peak potential difference in Example 1 is small and the peak shapes overlap in three cycles, while the peak shape shift in Comparative Example 1 is obvious, proving that Li + Doping improves structural reversibility.

[0039] This invention utilizes precise Li + Doping stabilizes the layered framework of P2-type layered oxides, Li + The stable Li-O covalent bond formed with O generates a "pillar effect," which can effectively suppress the irreversible P2-O2 phase transition under high voltage, alleviate lattice distortion and structural collapse during cycling, and significantly improve the cycling stability of the material. The resulting material exhibits excellent cycling stability at 100 mA·g. -1 The capacity retention rate can reach 86.1% after 100 cycles at current density; This invention employs a urea chelation-assisted hydrothermal method to prepare the precursor, achieving a uniform distribution of Mn and Fe transition metal ions. After subsequent high-temperature sintering, the material retains a secondary spherical particle morphology of 5-15 μm with a particle size of 3-20 μm. This morphology not only increases the contact area between the electrode and the electrolyte but also shortens the sodium ion transport path, effectively optimizing the interfacial kinetics of the material. This results in a charge transfer resistance as low as 66.0 Ω and a significantly improved rate performance at 500 mA·g. -1 It still exhibits high discharge specific capacity under high current density; The Li obtained in this invention + The doped P2-type layered oxide cathode material exhibits a pure hexagonal P2-type crystal structure with space group P63 / mmc and lattice parameters a = 4.75–4.83 Å, b = 4.75–4.83 Å, c = 15.5–15.8 Å. No impurity phases are formed, and Li... + The electrochemical structure reversibility of the doped material is greatly improved, the redox peak potential difference is small and the peak shape is stable. Combined with the optimized microstructure, the cycle stability, interfacial kinetics performance and rate performance are synergistically improved. The material has excellent comprehensive electrochemical performance and can be widely used in sodium-ion battery applications such as large-scale energy storage and low-speed power batteries.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the present invention.

Claims

1. A Li + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material, characterized in that... Includes the following steps: Step 1: Dissolve MnSO4·H2O and FeSO4·H2O in deionized water at an equimolar ratio to form a mixed solution with a transition metal ion concentration of 0.8~1.2 mol / L. Add urea to the mixed solution at a urea to transition metal ion molar ratio of (3~5):1, and stir until evenly dispersed. Transfer the solution to a hydrothermal reactor and react at 150~170℃ for 10~14 h. After cooling, filter, wash, and dry to obtain MnSO4·H2O. 0.5 Fe 0.5 CO3 precursor; Step 2, press Mn 0.5 Fe 0.5 The stoichiometric ratio of CO3 precursor, NaOH powder, and LiOH powder is 1:(0.55~0.70):(0.03~0.07). The raw materials are ground until uniformly mixed to obtain a mixed powder. The mixed powder is placed in a tube furnace and heated to 430~470℃ in air atmosphere for 4~6 h, then heated to 880~920℃ and held for 10~14 h. After natural cooling, Li is obtained. + P2-doped layered oxide sodium-ion battery cathode material.

2. The Li according to claim 1 + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material, characterized in that... The stirring described in step one is carried out at 20~30℃ for 4~6 hours.

3. The Li according to claim 1 + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material, characterized in that... The washing described in step one involves alternating between deionized water and anhydrous ethanol for 3 to 5 times each.

4. The Li according to claim 1 + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material, characterized in that... The drying process described in step one involves vacuum drying at 50-70°C for 10-14 hours.

5. The Li according to claim 1 + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material, characterized in that... The grinding and mixing time in step two is 30~60 min, and the particle size of the mixed powder is ≤50μm.

6. The Li according to claim 1 + A method for preparing a P2-doped layered oxide sodium-ion battery cathode material, characterized in that... The heating rate of the tubular furnace described in step two is 2~4℃ / min.

7. A Li prepared by the method according to any one of claims 1 to 6 + A P2-doped layered oxide sodium-ion battery cathode material, characterized in that... The stoichiometric formula is Na x Li y Mn 0.5 Fe 0.5 CO3O2, where x = 0.55~0.70 and y = 0.03~0.

07.

8. The Li according to claim 7 + A P2-doped layered oxide sodium-ion battery cathode material, characterized in that... It has a hexagonal P2 type crystal structure, space group P63 / mmc, lattice parameters a=4.75~4.83 Å, b=4.75~4.83 Å, c=15.5~15.8 Å, and exhibits a secondary spherical morphology with a particle size of 3~20 μm.

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