P2 type layered sodium ion positive electrode material based on Cu doping and MgO surface coating and preparation method of P2 type layered sodium ion positive electrode material

Abstract

The invention discloses a preparation method of a P2 type layered sodium ion positive electrode material based on Cu doping and MgO surface coating, and the preparation method comprises the following steps: (1) weighing raw materials according to a stoichiometric formula Na < 0.67 > Ni < 0.33-x > Cu < x > Mn < 0.67 > O < 2 >, and respectively dispersing the raw materials into distilled water, (2) sequentially and uniformly dispersing the dispersed solutions into an aqueous solution of citric acid, stirring in a microwave reactor, heating at the temperature of 100-110 DEG C until the solvent is completely evaporated to form green gel, grinding the gel into powder, pre-sintering at the temperature of 500-510 DEG C, taking out, uniformly grinding again, and roasting at the temperature of 950-1000 DEG C to obtain a roasted product; and (3) adding a C4H6MgO4. 4H2O solution into the roasted product suspension, stirring at the temperature of 80-90 DEG C until the solvent is completely evaporated, and roasting the powder at the temperature of 550-600 DEG C to obtain the product Na < 0.67 > Ni < 0.33-x > Cu < x > Mn < 0.67 > O < 2 > (at) y MgO. The structural stability, the interface stability and the dynamic performance of the material under a high-voltage condition are improved through a dual modification strategy of combining partial replacement of crystal lattices by copper ions (Cu < 2 + >) and surface coating of magnesium oxide (MgO).

Description

Technical Field

[0001] This invention relates to the field of sodium ion cathode material technology, specifically to a P2-type layered sodium ion cathode material based on Cu doping and MgO surface coating, and its preparation method. Background Technology

[0002] Sodium-ion batteries (SIBs), as a low-cost alternative to lithium-ion batteries, have attracted widespread attention from researchers in recent years due to the abundance and low price of sodium resources. However, the cathode material remains a key limiting factor in achieving high energy density and long cycle life.

[0003] P2 type layered oxides (general formula Na) x TMO2 has become a research hotspot due to its large interlayer spacing and excellent rate performance, among which Na 0.67 Ni 0.33 Mn 0.67 O2 is considered a promising cathode material due to its high specific capacity and low cost. However, during high-voltage charging and discharging, it is prone to the P2 → O2 phase transition, accompanied by Na layer slippage and drastic volume changes, which leads to cycle decay, microcrack formation and exacerbation of electrolyte side reactions. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating, and its preparation method. This is achieved through the use of copper ions (Cu... 2+ A dual modification strategy combining partial lattice substitution and magnesium oxide (MgO) surface coating was adopted to improve the structural stability, interfacial stability and kinetic properties of the material under high voltage conditions.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating, characterized by the following steps:

[0006] (1) According to the stoichiometric formula Na 0.67 Ni 0.33-x Cu x Mn 0.67 O2, weigh out CH3COONa, NiC4H6O4·4H2O, MnC4H6O4·4H2O, and C4H6CuO4·H2O, and disperse them separately in distilled water.

[0007] (2) Disperse the well-dispersed solution into the aqueous solution of citric acid in sequence, then stir in a microwave reactor and heat at 100-110℃ until the solvent is completely evaporated to form a green gel. Grind the gel into powder, pre-calcine at 500-510℃, take it out and grind it evenly again, and then calcine it at 950-1000℃ to obtain the calcined product.

[0008] (3) Dissolve C4H6MgO4·4H2O in anhydrous ethanol, disperse the calcined product in anhydrous ethanol to form a suspension, add the C4H6MgO4·4H2O solution to the calcined product suspension, stir at 80-90℃ until the solvent is completely evaporated, and calcine the powder at 550-600℃ to obtain product Na. 0.67 Ni 0.33-x Cu x Mn 0.67 O2@yMgO.

[0009] In the above scheme: x = 0.03-0.15, and the mass fraction of MgO y is 1-5wt%.

[0010] Preferred: x = 0.05, y = 3 wt%.

[0011] In the above scheme, the molar ratio of citric acid to transition metal ions (Ni, Mn, Cu) is 1:1.

[0012] In the above scheme: in step (2), preheat for 5-6 hours.

[0013] In the above scheme: in step (2), the calcination time is 10-12h and the heating rate is set to 3 ℃ / min.

[0014] In the above scheme: in step (3), roasting is carried out for 5-6 hours.

[0015] The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating yields a P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating.

[0016] This invention is in Na 0.67 Ni 0.33 Mn 0.67 O2 matrix partially uses Cu 2+ Replace Ni 2+ (Constitutes Na) 0.67 Ni 0.33- x Cu x Mn 0.67Cu-MgO dual modification (hereinafter referred to as "Cu-MgO dual modification" or "bulk-boundary dual strategy") can simultaneously suppress the high-voltage P2-O2 phase transition and significantly reduce interfacial side reactions. It has a low average particle size and exhibits high discharge capacity, excellent rate performance, and good cycle stability in electrochemical performance. It is a promising sodium-ion layered nickel-manganese-based cathode material. Attached Figure Description

[0017] Figure 1 for Na 0.67 Ni 0.33-x Cu x Mn 0.67 Schematic diagram of the synthesis process of O2@yMgO sample.

[0018] Figure 2 For NM and Na 0.67 Ni 0.33-x Cu x Mn 0.67 XRD patterns of O2 (x=0.03,0.05,0.1,0.15).

[0019] Figure 3 for (a) Na 0.67 Ni 0.33-x Cu x Mn 0.67 Cyclic performance of O2 (x=0.03,0.05,0.1,0.15) at 1C and (b) rate performance.

[0020] Figure 4 The X-ray diffraction patterns of samples NM, NCM, NCM@1MgO, NCM@2MgO, NCM@3MgO and NCM@5MgO are shown in the right figure, which shows the shift of the main XRD peak.

[0021] Figure 5 The XRD patterns of samples (a) NM, (b) NCM, (c) NCM@1MgO, (d) NCM@2MgO, (e) NCM@3MgO and (f) NCM@5MgO are shown.

[0022] Figure 6 SEM images of samples (a) NM, (b) NCM, (c) NCM@1MgO, (d) NCM@2MgO, (e) NCM@3MgO and (f) NCM@5MgO.

[0023] Figure 7 TEM images of samples (a) NM and (b) NCM@3MgO, and atomic-level EDS spectrum of NCM@3MgO (c).

[0024] Figure 8 X-ray photoelectron spectra of NM, NCM, and NCM@3MgO: (a) full-spectrum scan; (b) Cu2p spectrum of NCM@3MgO and (c) Mg1s spectrum; (d) Ni2p spectrum and (e) Mn2p spectrum; (f) Mn2p spectrum. 3 / 2 Mn obtained by peak fitting 3+ / Mn 4+ ratio.

[0025] Figure 9 (a) Initial charge-discharge curves of NM and NCM@3MgO; (b) Charge-discharge curves of NM and (c) NCM@3MgO at 1C; (d) Cycling performance of NM, NCM, and NCM@3MgO at 0.1C; Electrochemical performance of NM, NCM, NCM@1MgO, NCM@2MgO, NCM@3MgO, and NCM@5MgO; (e) Cycling performance at 1C rate; (f) Rate performance; (g) Cycling performance at 5C.

[0026] Figure 10 The galvanostatic intermittent titration curves and corresponding sodium ion diffusion coefficients of (a) NM, (b) NCM, and (c) NCM@3MgO are shown; the cyclic voltammetry curves of (d) NM, (e) NCM, and (f) NCM@3MgO at different scan rates are shown; and the contribution ratios of capacitance control and diffusion control to (g) NM, (h) NCM, and (i) NCM@3MgO are shown.

[0027] Figure 11 The images show the off-site X-ray diffraction patterns of (a) NM and (b) NCM@3MgO cathode materials at different stages of the first cycle; and (c) and (d) schematic diagrams of the crystal structure evolution of NM and NCM@3MgO during the sodium ion insertion / extraction process.

[0028] Figure 12 The total density of states of (a) NM, (b) NCM and (c) NCM@3MgO; and the skewed densities of states of Ni3d, Mn3d, Cu3d, Mg2p and O2p electrons in (d) NM, (e) NCM and (f) NCM@3MgO.

[0029] Figure 13 XRD patterns of (a) NM, (b) NCM and (c) NCM@3MgO samples after cycling.

[0030] Figure 14 The C1s and F1s energy spectra of (a) NM and (b) NCM@3MgO samples after cycling. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0032] Example 1

[0033] Preparation of P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating:

[0034] I. Ingredient Design

[0035] (1) Weigh a certain mass of CH3COONa, NiC4H6O4·4H2O, MnC4H6O4·4H2O and C4H6CuO4·H2O materials according to the molar ratio of Na:Ni:Mn:Cu=0.67:0.33:0.67:0.05.

[0036] (2) Disperse the weighed sample in distilled water at room temperature and stir for 30 min. Then, disperse the solution evenly in citric acid aqueous solution (the molar ratio of citric acid to transition metal ions (Ni, Mn, Cu) is 1:1). Transfer the solution into a microwave reactor and heat at 100-110℃ until the solvent is completely evaporated to form a green gel.

[0037] (3) The gel was ground into powder and then transferred into a tube furnace. It was pre-calcined at 500-510 °C for 5 hours. After being taken out, it was ground uniformly again. Then, it was calcined at 950-1000 °C for 10 hours with a heating rate of 3 °C / min and an air atmosphere to obtain the calcined product Na. 0.67 Ni 0.28 Cu 0.05 Mn 0.67 O2 (NCM).

[0038] Simultaneously prepare Na according to steps (1)-(3). 0.67 Ni 0.33 Mn 0.67 O2(NM).

[0039] Na with different doping amounts was then prepared with x values ​​of 0.03, 0.1, and 0.15. 0.67 Ni 0.33-x Cu x Mn 0.67 O2.

[0040] The calcined NCM sample was ground and dispersed in anhydrous ethanol. C4H6MgO4·4H2O was dissolved in anhydrous ethanol, and the C4H6MgO4·4H2O solution was added to the calcined product suspension. The mixture was stirred at 80-90℃ until the solvent was completely evaporated. The powder was then calcined at 550-600℃ for 5 hours, and the powder was ground to obtain the Na product. 0.67 Ni 0.28 Cu 0.05Mn 0.67 O2@MgO sodium ion cathode material, with MgO mass fractions of 1wt%, 2wt%, 3wt%, and 5wt%, respectively, the resulting products are denoted as NCM@1MgO, NCM@2MgO, NCM@3MgO, and NCM@5MgO.

[0041] The organizational process of sodium-ion batteries, including the preparation of electrode sheets and the assembly of sodium-ion batteries, is as follows:

[0042] The sodium-ion battery positive electrode material, conductive agent (Super-P), and binder (PVDF) prepared according to the present invention were weighed and ground evenly in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added to form a viscous slurry, which was then evenly coated onto the surface of the current collector (aluminum foil) using a coating machine. The aluminum foil coated with the slurry was placed in a vacuum drying oven at 120°C and vacuum dried for 12 hours. The electrode sheet was then removed, rolled, sliced, and weighed on a roller press for later use. The positive electrode sheet, sodium sheet, spring sheet, gasket, positive electrode shell, negative electrode shell, separator, and electrolyte were assembled into a CR2023 type coin cell in an argon-filled glove box. The electrolyte was 1.0 mol / L NaClO4 + EC / DEC (volume ratio 1:1) + 5.0% FEC. The water and oxygen content in the glove box were both less than 0.01 ppm. Electrochemical tests were conducted on the Xinwei testing system, with a nominal specific capacity of 1C = 160mAh / g.

[0043] Performance testing:

[0044] like Figure 2 Different doping amounts of Na 0.67 Ni 0.33-x Cu x Mn 0.67 O2 (x=0.03, 0.05, 0.1, 0.15) exhibits a hexagonal P2-type structure with the P63 / mmc space group, indicating that Cu ion doping did not change the Na 0.67 Ni 0.33 Mn 0.67 The material exhibits a layered structure of O2, but when the doping concentration reaches 0.1%, CuO impurity peaks appear.

[0045] like Figure 3 The sample with a doping concentration of 0.05% exhibited the best electrochemical cycling performance and rate capability, retaining a capacity of 80.7 mAh g⁻¹ after 100 cycles at 1C. -1 The capacity retention rate is 80.97%, and it still exhibits 81.85 mAh g⁻¹ at a current density of 10C. -1 The discharge capacity.

[0046] Figure 4The X-ray diffraction patterns of samples NM, NCM, NCM@1MgO, NCM@2MgO, NCM@3MgO and NCM@5MgO are shown in the right figure, which shows the shift of the main XRD peak.

[0047] All NCM and NCM@MgO samples exhibited a hexagonal P2-type structure with the P63 / mmc space group, indicating that Cu ion doping and a small amount of MgO surface treatment did not alter the Na+ structure. 0.67 Ni 0.33 Mn 0.67 O2 has a layered structure.

[0048] from Figure 5 It can be observed that the lattice parameters a and c of the NCM and NCM@MgO samples are very close, but both are slightly larger than those of the NM sample. This can be attributed to Cu. 2+ The ionic radius (0.73 Å) is greater than that of Ni. 2+ The ionic radius is 0.69 Å. The change in lattice parameters after MgO coating can be attributed to the entry of a small number of Mg ions into the lattice during high-temperature calcination.

[0049] like Figure 6 As shown, NM, NCM, and NCM@3MgO are all large hexagonal particles with a diameter of approximately 2-5 μm, indicating that the MgO surface treatment has little effect on the morphology of NM. Furthermore, the surfaces of NM and NCM are relatively smooth and flat. In contrast, the surface of NCM@3MgO has some irregular particles attached, which is caused by the MgO surface treatment.

[0050] like Figure 7 High-resolution electron microscopy (HRTEM) images revealed an ultrathin amorphous MgO coating layer on the surface of the NCM@3MgO sample. The NM sample exhibited an ordered lattice pattern with uniform spacing. The spacing between adjacent lattice fringes was 0.2486 nm, corresponding to the (100) plane of the P2-type crystal structure. In contrast, NCM@3MgO showed significant differences between the bulk and surface regions. The lattice fringes in the bulk and surface regions were 0.25104 nm and 0.1541 nm, respectively, corresponding to the (100) and (002) planes of MgO. Compared to the NM sample, the NCM@3MgO sample showed a larger lattice fringes spacing, consistent with Rietveld's refinement results. Furthermore, EDS spectra indicated that Na, Mn, Ni, Cu, Mg, and O were relatively uniformly distributed throughout the material.

[0051] like Figure 8 As shown, compared with the NM sample, the Mn content of NCM and NCM@3MgO is higher. 3+ The content was significantly reduced, and the excess Mn 3+This can cause Jahn-Teller distortion, which destabilizes the layered structure and degrades its electrochemical performance.

[0052] Figure 9 The charge-discharge curves show that NCM@3MgO has a specific capacity of approximately 20 mAh g at 4.2V. -1 The specific capacity is lower than that of NM (approximately 60 mAh g). -1 This indicates that Cu 2+ The synergistic effect of doping and MgO surface modification can suppress the P2-O2 phase transition, resulting in a decrease in the charge specific capacity of NCM@3MgO at 4.2V. Figure 9 b and Figure 9 Figure c shows the charge-discharge curves of NM and NCM@3MgO electrodes after multiple cycles at 1C. The NCM@3MgO electrode maintains a clear voltage characteristic and a stable curve shape, indicating its excellent structural integrity during cycling. In contrast, the characteristic high-voltage plateau of the NM electrode disappeared after 100 cycles, indicating severe structural degradation.

[0053] The NCM@3MgO sample exhibited the best electrochemical performance, with a capacity of 95.1 mAh g after 60 cycles at 0.1C. -1 The retention rate was 90.31%, while the original sample only had a retention rate of 65.02 mAh g. -1 The retention rate was 50.41%; after 200 cycles at 1C, the capacity was 90.46 mAh g. -1 The capacity retention rate was 90.88%, far exceeding the 16.06% of the original sample; it still exhibited a capacity of 92.1 mAh g⁻¹ at a current density of 10 C. -1 The discharge capacity of the original sample was only 24.47 mAh g⁻¹. -1 .

[0054] like Figure 10 As shown, the results indicate that the Na in the NCM@3MgO sample... + Diffusion coefficient (7.43*10) -11 cm 2 s −1 The concentration was significantly higher than that of the NCM sample (6.81*10). -11 cm 2 s −1 ) and NM (2.35*10 -11 cm 2 s −1 ) sample. This finding indicates that Cu 2+ The dual-strategy modification of doping and synergistic MgO coating is beneficial to the kinetic process, leading to enhanced diffusion.

[0055] When the scan rate starts from 0.1 mV / s −1 Increment to 1.0 mV S −1 The capacitive contribution of NCM@3MgO (from 82% to 98.6%) was significantly higher than that of NM (from 70.3% to 96.9%) and NCM (from 75.8% to 97.3%). This trend indicates that the storage behavior of NCM@3MgO is mainly influenced by the capacitive effect. This quasi-capacitive storage mechanism is beneficial for fast reaction kinetics, thereby improving the long-term cycling performance of the electrode.

[0056] Figure 11 In the NCM@3MgO, from OCP to 4.0V, the NCM remains in the P2 phase with only a slight shift in the (002) peak. When further charged to 4.3V, the (002) peak shifts to a lower angle, attributed to the P2-O2 phase transition, and a new diffraction peak at approximately 20° is observed, indicating the O2 phase. In contrast, from OCP to 4.3V, the NCM@3MgO shows only a slight shift in the (002) peak to a lower angle, with no obvious (002) peak of the O2 phase observed, exhibiting a pure P2 phase. This indicates that the P2-O2 phase transition is effectively suppressed throughout the charge-discharge process.

[0057] like Figure 12 The results show that the dual-strategy modification significantly increases the density of states near the Fermi level (Ef), indicating a reduction in electron migration resistance at the Fermi level. Therefore, NCM@3MgO exhibits excellent electronic conductivity, which is beneficial for charge transfer in electrochemical processes. The off-center density of states (pDOS) is as follows: Figure 10 As shown in df, Cu 2+ After synergistic modification by doping and MgO surface coating, the overlap between O-2p and TM-3d near the Fermi level is enhanced, indicating the formation of stronger Mn-O and Ni-O bonds, which suppresses the slippage of the transition metal layer and thus effectively suppresses the phase transition.

[0058] like Figure 13 Numerous cracks were observed in the NM sample, while the number of cracks was significantly reduced in the NCM sample, and almost no cracks were visible in the NCM@3MgO sample.

[0059] like Figure 14 In the C1S spectrum, the intensities of the CO and C=O peaks corresponding to the decomposition of carbonate solvents in the NM electrode are higher than those in the NCM@3MgO electrode. Furthermore, in the F1S spectrum, the CF peak (688.09 eV) of polyvinylidene fluoride (PVDF) and the Na-F peak (685.38 eV) generated from the decomposition of fluoroethylene carbonate (FEC) are observed, with the Na-F peak intensity of the NM electrode being higher than that of the NCM@3MgO electrode.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating, characterized in that, Prepare according to the following steps: (1) According to the stoichiometric formula Na 0.67 Ni 0.33-x Cu x Mn 0.67 O2, weigh out CH3COONa, NiC4H6O4·4H2O, MnC4H6O4·4H2O, and C4H6CuO4·H2O, and disperse them separately in distilled water. (2) Disperse the well-dispersed solution into the aqueous solution of citric acid in sequence, then stir in a microwave reactor and heat at 100-110℃ until the solvent is completely evaporated to form a green gel. Grind the gel into powder, pre-calcine at 500-510℃, take it out and grind it evenly again, and then calcine it at 950-1000℃ to obtain the calcined product. (3) Dissolve C4H6MgO4·4H2O in anhydrous ethanol, disperse the calcined product in anhydrous ethanol to form a suspension, add the C4H6MgO4·4H2O solution to the calcined product suspension, stir at 80-90℃ until the solvent is completely evaporated, and calcine the powder at 550-600℃ to obtain product Na. 0.67 Ni 0.33-x Cu x Mn 0.67 O2@yMgO.

2. The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating according to claim 1, characterized in that: x = 0.03-0.15, and the mass fraction of MgO y is 1-5 wt%.

3. The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating according to claim 1 or 2, characterized in that: x is 0.05 and y is 3 wt%.

4. The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating according to claim 3, characterized in that: The molar ratio of citric acid to transition metal ions is 1:

1.

5. The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating according to claim 4, characterized in that: In step (2), preheat for 5-6 hours.

6. The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating according to claim 5, characterized in that: In step (2), the calcination time is 10-12 hours and the heating rate is set to 3 °C / min.

7. The method for preparing P2-type layered sodium-ion cathode material based on Cu doping and MgO surface coating according to claim 6, characterized in that: In step (3), roasting is carried out for 5-6 hours.

8. A P2-type layered sodium-ion cathode material prepared by the method of any one of claims 1-7 based on Cu doping and MgO surface coating.

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