A sodium-ion layered oxide material with a coating layer and a preparation method and application thereof

Abstract

The present invention discloses a sodium ion layered oxide material with a coating layer. The structural general formula of the sodium ion layered oxide in this material is NaxTMO2, including at least one of the O3 type and the P2 type; the coating layer is molybdenum disulfide and conductive carbon, and the TM is a combination of at least two of the transition metal elements Ni, Fe, Cu, Ti, Ag and the Mn element; the x is a positive number, and 0 < x ≤ 1. The present invention also discloses a preparation method and application of the above material. The material prepared by the method of the present invention can both effectively improve the rate performance of the material by constructing a continuous electron conduction network; and can regulate the formation process of the active sites on the positive electrode surface and the electrolyte interface layer, thereby reducing the interface transfer impedance during the ion deintercalation process; in addition, the surface coating can isolate the erosion of the humid air on the positive electrode material and inhibit the side reaction between it and the electrolyte. Therefore, the cycle stability of the composite coated layered oxide material is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials, specifically to a sodium-ion layered oxide material with a coating layer, its preparation method, and its application. Background Technology

[0002] Layered oxide cathode materials for sodium-ion batteries have attracted widespread attention due to their high operating voltage, considerable specific capacity, and simple synthesis process. However, under high-voltage operating conditions, these materials are prone to irreversible phase transitions accompanied by oxygen evolution. Oxygen evolution disrupts the surface structure of the material, thereby exacerbating interfacial side reactions between the material and the electrolyte. These side reactions form a thick solid electrolyte interphase (SEI) film during cycling, severely limiting the long-term cycling stability of the material. Furthermore, the high chemical reactivity of sodium makes layered oxides susceptible to Na⁺ / H⁺ exchange reactions in air, leading to the release of sodium ions from the crystal lattice and the generation of insulating byproducts such as Na₂CO₃, NaHCO₃, and NaOH. To overcome these limitations, researchers have extensively explored various modification strategies, mainly including heteroatom doping and surface coating. Heteroatom doping, by controlling the interlayer spacing in the layered structure, helps improve the overall structural stability of the material. However, this method mainly affects the bulk structure of the material and is difficult to effectively suppress oxygen evolution, side reactions, and irreversible phase transitions occurring on the material surface. In contrast, surface coating is considered a more effective strategy to mitigate surface degradation, as it can prevent positive electrode particles from being directly exposed to the electrolyte and humid air.

[0003] For example, Shi et al. [Acs Applied Materials & Interfaces, 2019, 11(27): 24122] in Na 0.78 Al 0.05 Ni 0.33 Mn 0.6 An Al2O3 coating was applied to the surface of the O2 cathode. This coating significantly suppressed the P2→O2 phase transition under high voltage, while mitigating irreversible side reactions and reducing unstable Mn / Ni species with high valence states generated by transition metal oxidation, thus effectively preventing the phase transition. The modified material achieved a specific capacity of 145.2 mAh g⁻¹, with a capacity retention of 85.1% after 100 cycles. However, the sodium ion conductivity of such metal oxide coatings is generally low, limiting the ion migration rate at the electrode-electrolyte interface. Dai et al. [Small, 2024, 20(2): 2305019] applied Al2O3 to NaNi... 1 / 3 Fe 1 / 3 Mn 1 / A sodium metaphosphate (NaPO3) nanolayer was constructed on the surface of 3O2. This coating not only provides a rapid diffusion channel for sodium ions but also effectively suppresses electrolyte side reactions, improving the stability of the material under high voltage. However, sodium metaphosphate has strong hygroscopicity, which is detrimental to the storage stability of the cathode material in air.

[0004] In summary, effectively suppressing interfacial side reactions in layered oxide materials and improving their electrochemical performance and air storage stability has become a key scientific problem that urgently needs to be solved in the preparation of cathode materials for sodium-ion batteries. Summary of the Invention

[0005] To address the poor air storage and cycle performance of existing sodium-ion battery layered oxide cathode materials, this invention provides a sodium-ion layered oxide material with a coating layer, wherein the coating layer is a composite layer of molybdenum disulfide and conductive carbon. The general structural formula of the sodium-ion layered oxide is NaxTMO2, including at least one of O3-type and P2-type sodium-ion layered oxide materials. Wherein, TM is a combination of at least two transition metal elements Ni, Fe, Cu, Ti, and Ag, and Mn; x is a positive number, and 0 < 0 < 1. <x≤1。

[0006] Furthermore, the mass of the coating layer accounts for 9% to 25% of the mass of the sodium ion layered oxide material having the coating layer.

[0007] Furthermore, the molybdenum disulfide accounts for 4% to 10% of the mass of the coated sodium ion layered oxide material, and the conductive carbon accounts for 5% to 15% of the mass of the coated sodium ion layered oxide material.

[0008] This invention also provides a method for preparing the above-mentioned sodium ion layered oxide material. This method employs a simple high-energy ball milling coating technique to obtain a layered oxide material with a uniform surface coating of MoS2 and conductive carbon. When used as a cathode material, it can effectively suppress the degradation of the bulk phase and interface during cycling, achieving a significant improvement in cycle stability.

[0009] The preparation method of the present invention is achieved through the following technical solution: 1) After the transition metal source precursors and sodium source are pre-reacted by high-energy ball milling, they are pressed into tablets using a tablet press and then calcined at high temperature to obtain sodium ion layered oxide with the general structural formula NaxTMO2. The metal elements contained in the transition metal source precursors, in addition to Mn, also contain at least two of Ni, Fe, Cu, Ti and Ag.

[0010] 2) Sodium ion layered oxide, MoS2 and conductive carbon are mixed and ball-milled to coat the surface of sodium ion layered oxide with MoS2 and conductive carbon, resulting in a sodium ion layered oxide material with the chemical formula NaxTMO2@MoS2 / C.

[0011] Furthermore, the transition metal source precursor is at least one selected from transition metal nitrate, transition metal acetate, transition metal oxide, and transition metal hydroxide.

[0012] Furthermore, each of the transition metal source precursors contains at least one metal element selected from Ni, Mn, Fe, Cu, Ag, and Ti.

[0013] Furthermore, the sodium source is at least one of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0014] Furthermore, the calcination reaction is carried out at a temperature of 850℃ to 1000℃ for 12 to 18 hours, and the atmosphere for the calcination reaction is air.

[0015] Furthermore, the high-energy ball milling time is 10–24 h, and the ball milling speed is 200–450 rpm.

[0016] The present invention also provides the application of the above-mentioned sodium-ion battery layered oxide material with coating as a positive electrode material for sodium-ion batteries.

[0017] The beneficial effects of this invention are: This invention employs a simple and easily implemented ball milling coating method to coat the surface of a sodium-ion layered oxide material with a layer of MoS2 and conductive carbon. This reduces side reactions between the cathode material surface and the electrolyte, improves interfacial stability, inhibits the dissolution of transition metal ions, and utilizes the two-dimensional layered structure of MoS2 to regulate the active sites on the cathode surface and the carbon coating layer to construct a continuous electron conduction network. It also reduces the structural degradation of the layered oxide cathode material during cycling and improves structural stability. Therefore, this invention can effectively improve the electrochemical performance and air stability of sodium-ion batteries. Attached Figure Description

[0018] Figure 1 The X-ray diffraction (XRD) patterns of the cathode materials prepared in Examples 1-5 and 9-11 are shown.

[0019] Figure 2 XPS images of the cathode materials prepared in Examples 1 and 5. Figure 3 The images show the electrochemical impedance spectroscopy (EIS) diagrams of the cathode materials prepared in Examples 1-5 and 9-11.

[0020] Figure 4 The graph shows the electrochemical cycling performance of the batteries assembled in Examples 1-4, 6, 9-11. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0022] Sodium ion layered oxide materials are prepared by the following method: (1) Sodium carbonate, nickel acetate, ferric oxide and manganese dioxide are thoroughly mixed in a stoichiometric ratio of 1.6:1:0.5:1, a small amount of ethanol is added, and the mixture is wet ball-milled, dried and ground to obtain the precursor. (2) The precursor was pressed into discs under 10 MPa pressure and then placed in a muffle furnace for sintering at 900 °C for 16 h. After cooling, the sintered product was obtained. Subsequently, the sintered product was crushed and ground to obtain layered oxide powder with the molecular formula NaNi. 1 / 3 Fe 1 / 3Mn 1 / 3 O2; denoted as NFM. Example

[0023] (1) Sodium carbonate, nickel acetate, manganese dioxide, copper acetate, titanium dioxide and silver nitrate were thoroughly mixed in a stoichiometric ratio of 4.2:3:4:1:1:1, wet-milled using a planetary ball mill, dried and ground to obtain the precursor; (2) The precursor was pressed into discs and placed in a muffle furnace for sintering at 900°C for 12 hours. After cooling, the sintered product was obtained. Subsequently, the sintered product was crushed, ground, and sieved to obtain layered oxide powder with the molecular formula Na. 0.8 Ni 0.3 Mn 0.4 Cu 0.1 Ti 0.1 Ag 0.1 O2, denoted as NMCTA. Example

[0024] (1) Sodium carbonate, nickel oxide, manganese dioxide, copper acetate, titanium dioxide, ferric oxide and silver nitrate were thoroughly mixed in a stoichiometric ratio of 4.7:3:4:1:1:0.2:0.8, wet ball milled using a planetary ball mill, dried and ground to obtain the precursor; (2) The precursor was pressed into discs and placed in a muffle furnace for sintering at 900°C for 12 hours. After cooling, the sintered product was obtained. Subsequently, the sintered product was crushed, ground, and sieved to obtain layered oxide powder with the molecular formula Na. 0.9 Ni 0.3 Mn 0.4 Cu 0.1 Ti 0.1 Ag 0.02 Fe 0.08 O2, denoted as NMCTAF0.9. Example

[0025] (1) Sodium carbonate, nickel oxide, manganese dioxide, copper acetate, titanium dioxide, ferric oxide and silver nitrate were thoroughly mixed in a stoichiometric ratio of 5.25:3:4:1:1:0.2:0.8, wet-milled using a planetary ball mill, dried and ground to obtain the precursor; (2) The precursor was pressed into discs and placed in a muffle furnace for sintering at 900°C for 12 hours. After cooling, the sintered product was obtained. Subsequently, the sintered product was crushed, ground, and sieved to obtain layered oxide powder with the molecular formula NaNi. 0.3 Mn 0. 4Cu 0.1 Ti 0.1 Ag 0.02 Fe 0.08 O2, denoted as NMCTAF1. Example

[0026] Weigh out 0.5 g of MoS2, 1.5 g of carbon powder, and 7.5 g of sodium ion layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was ball-milled at 300 rpm for 20 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NFM-MS. Example

[0027] Weigh out 1.0 g of MoS2, 1.0 g of carbon powder, and 8.0 g of sodium ion layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was ball-milled at 200 rpm for 24 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NFM-MS1. Example

[0028] Weigh out 0.4 g of MoS2, 1.0 g of carbon powder, and 7.9 g of sodium ion layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3O2 was ball-milled at 300 rpm for 20 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NFM-MS2. Example

[0029] Weigh out 0.8 g of MoS2, 0.5 g of carbon powder, and 8.7 g of sodium ion layered oxide NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was ball-milled at 400 rpm for 10 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NFM-MS3. Example

[0030] Weigh out 0.4 g of MoS2, 1 g of carbon powder, and 8.5 g of sodium ion layered oxide cathode material Na. 0.8 Ni 0.3 Mn 0.4 Cu 0.1 Ti 0.1 Ag 0.1 O2 was ball-milled at 400 rpm for 12 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NMCTA-MS. Example

[0031] Weigh out 1 gram of MoS2, 1.5 grams of carbon powder, and 10 grams of sodium ion layered oxide cathode material Na. 0.9 Ni 0.3 Mn 0.4 Cu 0.1 Ti 0.1 Ag 0.02 Fe 0.08 O2 was ball-milled at 350 rpm for 16 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NMCTAF0.9-MS. Example

[0032] Weigh out 1 gram of MoS2, 1 gram of carbon powder, and 8 grams of sodium ion layered oxide cathode material NaNi. 0.3 Mn 0.4 Cu 0.1 Ti 0.1 Ag 0.02 Fe 0.08 O2 was ball-milled at 200 rpm for 20 hours to obtain a sodium-ion layered oxide cathode material with MoS2 / C composite coating, denoted as NMCTAF1-MS.

[0033] The cathode materials prepared in some of the embodiments were characterized by phase composition, electrochemical performance, and air stability tests. The results are as follows: Figure 1 XRD patterns of the cathode materials prepared in Examples 1-5, 9-11. Figure 1 (a) It can be seen that the diffraction peaks of samples NFM and NFM-MS match the diffraction peaks of the O3 phase standard diffraction card (PDF#54-0887), respectively. This result confirms that both samples exhibit an O3 phase layered structure. The XRD patterns of samples NNMCAT, NNMCAT-MS, NNMCATF0.9, NNMCATF0.9-MS, NNMCATF1, and NNMCATF1-MS are shown below. Figure 1 As shown in (a) and (b), the diffraction peaks correspond to those of the P2 phase (PDF#54-0894), indicating that they both possess a P2-type layered structure. The coated sample exhibited a characteristic MoS2 peak at 14.7°, and the positions of the characteristic diffraction peaks in the XRD pattern did not change significantly after coating with MoS2 / C. This confirms that MoS2 was successfully coated onto the material surface without inducing a significant transformation in the bulk structure.

[0034] Figure 2 The XPS spectra of Examples 1 and 5 show that the sample of Example 1 contains elements such as iron, manganese, nickel, and oxygen. The sample of Example 5, in addition to these elements, also contains Mo and S. After coating, the peak intensities of iron, manganese, nickel, and oxygen weaken, indicating a decrease in the surface layer content of these elements. Comparing the fine spectra of Mn before and after coating reveals that Mn... 3+ and Mn 4+ The change in the proportion of the two valence states before and after coating indicates that during the coating process, a chemical reaction occurred between the coating layer and the matrix material, resulting in a tight coating on the surface layer.

[0035] Figure 3 Electrochemical impedance spectroscopy (EIS) of the cathode materials prepared in Examples 1-5 and 9-11 is shown. Figure 3 It can be seen that the charge transfer resistance of the coated sample is significantly reduced, which is beneficial to improving the rate performance of the material.

[0036] Figure 4 The cycle performance and rate performance of the cathode materials prepared in Examples 1-4, 6, 9-11 are analyzed. Figure 4 It can be seen that after coating, the synthetic material exhibits improved cycle performance and rate capability during charge and discharge. This may be attributed to its good conductivity and the surface coating layer's ability to block side reactions in the electrolyte.

[0037] To investigate the air stability of the cathode materials prepared in Examples 1-11, the pH of the cathode materials after immersion in water was tested. The pH was tested as follows: 1 g of material was immersed in 10 ml of deionized water for 15 min, and the pH value of the aqueous solution was recorded. The results are shown in Table 1. Table 1 shows that during air exposure, the surface layered structure of the uncoated material underwent Na+ oxidation. + / H + The PVDF exchange and adsorbs CO2 from the air, generating alkaline substances such as NaOH and Na2CO3. During electrode coating, the PVDF binder undergoes defluorination and degradation in an alkaline environment, leading to binder failure and insufficient adhesion, resulting in coating difficulties. However, the pH of the samples after surface coating is lower than that of the uncoated samples. This is attributed to the physical barrier formed by the MoS2 coating layer on the material surface, reducing the formation of alkaline substances and improving the material's air stability.

[0038]

[0039] The above descriptions are merely a few embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the protection scope of the present invention.

Claims

1. A sodium ion layered oxide material having a coating layer, characterized in that, The chemical formula of the sodium ion layered oxide material with the coating layer is NaxTMO2@MoS2 / C, wherein the general structural formula of the sodium ion layered oxide is NaxTMO2, including at least one of O3-type sodium ion layered oxide materials and P2-type sodium ion layered oxide materials; the coating layer is a composite layer of molybdenum disulfide and conductive carbon, and TM is a combination of at least two of the transition metal elements Ni, Fe, Cu, Ti, and Ag and Mn; x is a positive number, and 0 <x≤1。 2. The sodium ion layered oxide material with a coating layer according to claim 1, characterized in that, The mass of the coating layer accounts for 9% to 25% of the mass of the sodium ion layered oxide material having the coating layer.

3. The sodium ion layered oxide material with a coating layer according to claim 1 or 2, characterized in that, The molybdenum disulfide accounts for 4% to 10% of the mass of the coated sodium ion layered oxide material, and the conductive carbon accounts for 5% to 15% of the mass of the coated sodium ion layered oxide material.

4. A method for preparing a sodium ion layered oxide material with a coating layer, characterized in that, The preparation method includes the following steps: 1) After the transition metal source precursors and sodium source are pre-reacted by high-energy ball milling, they are pressed into tablets using a tablet press and then calcined at high temperature to obtain sodium ion layered oxide with the general structural formula NaxTMO2. The metal elements contained in the transition metal source precursors, in addition to Mn, also contain at least two of Ni, Fe, Cu, Ti and Ag. 2) Sodium ion layered oxide, MoS2 and conductive carbon are mixed and ball-milled to coat the surface of sodium ion layered oxide with MoS2 and conductive carbon, resulting in a sodium ion layered oxide material with the chemical formula NaxTMO2@MoS2 / C.

5. The method for preparing the sodium ion layered oxide material with a coating layer according to claim 4, characterized in that, The transition metal source precursor is at least one of transition metal nitrate, transition metal acetate, transition metal oxide, and transition metal hydroxide.

6. The method for preparing a sodium ion layered oxide material with a coating layer according to claim 4 or 5, characterized in that, Each of the transition metal source precursors contains at least one metal element selected from Ni, Mn, Fe, Cu, Ag, and Ti.

7. The method for preparing a sodium ion layered oxide material with a coating layer according to claim 4 or 5, characterized in that, The sodium source is at least one of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

8. The method for preparing a sodium ion layered oxide material with a coating layer according to claim 4 or 5, characterized in that, The calcination reaction is carried out at a temperature of 850℃~1000℃ for 12~18h, and the atmosphere for the calcination reaction is air.

9. The method for preparing a sodium ion layered oxide material with a coating layer according to claim 4 or 5, characterized in that, The high-energy ball milling time is 10-24 hours, and the ball milling speed is 200-450 rpm.

10. The application of the sodium-ion battery layered oxide material with a coating layer as a cathode material of a sodium-ion battery according to any one of claims 1 to 3.

Images