A modification method for surface reconstruction of layered oxide cathode materials in sodium-ion batteries induced by acid etching

Abstract

This invention discloses a modification method for acid etching-induced surface reconstruction of layered oxide cathode materials for sodium-ion batteries. The modification method includes: mixing sodium carbonate and nickel-iron-manganese hydroxide until homogeneous to obtain a first mixture; holding the first mixture at 800-1000°C in air and cooling to room temperature to obtain a sodium-based layered oxide host material; mixing the sodium-based layered oxide host material with a modification solution, etching for 0.5-2 hours, washing, and drying to obtain a second mixture, the modification solution including acetic acid; grinding the second mixture into powder, holding at 350-650°C in air and cooling to room temperature to obtain the sodium-ion battery layered oxide cathode material. This invention successfully achieves in-situ reconstruction of the surface structure using a simple acid etching method, forming a stable amorphous layer on the surface of the sodium-based layered oxide host material as a surface protective layer, enhancing hydrophobicity and air stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and specifically relates to a modification method for surface reconstruction of layered oxide cathode materials for sodium-ion batteries induced by acid etching. Background Technology

[0002] Lithium-ion batteries (LIBs) are widely used in everyday scenarios such as mobile electronic devices and electric vehicles. However, the limited reserves of lithium resources have prompted researchers to urgently seek alternative energy storage systems. Sodium-ion batteries (SIBs), due to their abundant sodium resources and advantages such as safety and environmental friendliness, are considered one of the most promising alternatives to lithium-ion batteries.

[0003] As a core component of sodium-ion batteries, the cathode material plays a crucial role in the overall performance of the battery. Among the many cathode materials for sodium-ion batteries, layered oxides have attracted widespread attention due to their potential high energy density and relatively simple synthesis process. The chemical formula of sodium-based layered oxides is Na. x TMO2 consists of alternating layers of transition metal (TM) and sodium. Based on the arrangement and occupancy of sodium ions, it can be classified into two typical configurations: P2 type and O3 type. Compared to P2, the O3 type layered oxide has an ABCABC stacking sequence in its crystal structure. This structure can accommodate more sodium ions, thus possessing a higher theoretical capacity. However, due to the large radius of sodium ions (1.02 Å), their insertion / extraction process in the electrode material is accompanied by changes in electronic structure, inevitably triggering irreversible structural transformations in the electrode material, leading to rapid capacity decay and structural collapse. Furthermore, the inherent high air sensitivity of O3 type layered transition metal oxides also results in high electrode manufacturing costs and performance degradation. Therefore, fundamental structural stability and air stability issues need to be addressed at the material level.

[0004] To address these issues, recent research has primarily focused on bulk doping and surface modification. However, bulk doping cannot effectively prevent electrolyte side reactions and air sensitivity defects. This is because the dopant elements are uniformly distributed within the cathode material, failing to form a dense protective layer, while side reactions and air-induced degradation mainly occur on the cathode material surface. While surface modification methods, such as conventional surface coating, can improve structural and air stability, current coating methods typically employ physical sintering or wet chemical methods. Physical sintering consumes considerable energy and requires strict control over the dimensions of the host material, making it difficult to obtain an ideal coating layer. Wet chemical methods, which usually use deionized water as a solvent, are unsuitable for preparing electrodes sensitive to moisture, such as those made of O3-type oxides. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a modification method for acid etching-induced surface reconstruction of layered oxide cathode materials for sodium-ion batteries. Irreversible structural transformations and interfacial side reactions during cycling limit the cycle life and rate performance of sodium-ion batteries. Furthermore, residual alkali on the surface of layered oxide cathode materials and their inherent high air sensitivity also contribute to performance degradation. To solve these problems, the present invention proposes a modification method for acid etching-induced surface reconstruction of layered oxide cathode materials for sodium-ion batteries.

[0006] Another object of the present invention is to provide a highly air-stable sodium-ion battery layered oxide cathode material obtained by the above-mentioned modification method of acid etching-induced surface reconstruction of sodium-ion battery layered oxide cathode material.

[0007] Another object of the present invention is to provide a sodium-ion battery.

[0008] The objective of this invention is achieved through the following technical solution.

[0009] A method for modifying the surface of a layered oxide cathode material for sodium-ion batteries by acid etching-induced surface reconstruction includes the following steps:

[0010] Step 1: Sodium carbonate (Na2CO3) and nickel-iron-manganese hydroxide are mixed until homogeneous to obtain a first mixture. The first mixture is then kept at 800-1000℃ for 10-15 hours in air, and cooled to room temperature to obtain a sodium-based crystalline oxide substrate material (the structural formula of the sodium-based crystalline oxide substrate material is NaNi). 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), wherein, by molar amounts, the ratio of sodium carbonate to nickel-iron-manganese hydroxide is (1~1.08):1, and the structural formula of nickel-iron-manganese hydroxide is Ni 1 / 3 Fe 1 / 3Mn 1 / 3 (OH)2;

[0011] Step 2: Mix the sodium-based crystalline oxide substrate material and the modification solution, etch for 0.5 to 2 hours, wash, and dry to obtain a second mixture. The modification solution includes a solute and a solvent. The solute is acetic acid, and the concentration of the solute in the modification solution is 0.1 to 0.9 M.

[0012] In step 2, the ratio of the mass fraction of the sodium-based crystalline oxide substrate to the volume fraction of the modified solution is 1:(100~500), with the mass fraction in g and the volume fraction in mL.

[0013] In step 2, the sodium-based crystalline oxide substrate material and the modified solution are mixed and etched at room temperature and under ultrasonic conditions for 0.5 to 2 hours.

[0014] In step 2, the solvent is an alcohol solvent.

[0015] In the above technical solution, the alcohol solvent is at least one of anhydrous ethanol and ethylene glycol.

[0016] In step 2, the drying temperature is 80~120℃ and the drying time is 3~5 hours.

[0017] Step 3: Grind the second mixture into powder, keep it at 350~650°C for 3~10 hours in an air atmosphere, and cool it to room temperature to obtain the sodium-ion battery layered oxide cathode material.

[0018] In step 3, the heating rate to 350~650°C is 5~10 °C / min.

[0019] The above-mentioned modification method of acid etching-induced surface reconstruction of sodium-ion battery layered oxide cathode material yields a highly air-stable sodium-ion battery layered oxide cathode material.

[0020] A sodium-ion battery includes: a highly air-stable layered oxide cathode material for sodium-ion batteries.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention successfully reconstructs the surface structure in situ using a simple acid etching method, forming a stable amorphous layer as a surface protective layer on the surface of the sodium-based layered oxide host material. This also effectively removes residual alkalis (such as NaOH, NaHCO3, and Na2CO3) from the surface of the sodium-based layered oxide host material. The functions of the amorphous layer include: firstly, acting as a physical barrier, preventing direct contact between the highly air-stable sodium-ion battery layered oxide cathode material and air, thus enhancing hydrophobicity and air stability; secondly, acting as a fast ion-conducting layer, enhancing the electron transfer capability and surface active sites within the cathode material, significantly promoting the formation of Na+. + The transport of ions provides richer ion diffusion pathways; finally, the amorphous layer can also mitigate the structural collapse and cracking of the cathode material during cycling, resulting in a superior electrochemical performance. Attached Figure Description

[0023] Figure 1 The images show the XRD patterns of the highly air-stable layered oxide cathode materials for sodium-ion batteries prepared in Examples 1-3.

[0024] Figure 2 The XRD patterns of the sodium-ion battery cathode materials prepared in Comparative Examples 1-4 are shown.

[0025] Figure 3 SEM image of the highly air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1;

[0026] Figure 4 The image shows an HRTEM image of the highly air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1.

[0027] Figure 5 Here is a SEM image of the sodium-ion battery cathode material prepared in Comparative Example 1;

[0028] Figure 6 Here is an HRTEM image of the sodium-ion battery cathode material prepared in Comparative Example 1;

[0029] Figure 7 To compare the sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1 at 15 mA g. -1 Charge-discharge curves at current density;

[0030] Figure 8 To compare the sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1, the test was conducted at 300 mA g. -1 Cyclic performance at current density;

[0031] Figure 9 To compare the sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1, the test was conducted at 750 mA g. -1 Cyclic performance at current density;

[0032] Figure 10 The rate performance graphs are shown for the sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared from the cathode material of Comparative Example 1.

[0033] Figure 11 To illustrate the application of the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 2 in Example 1, at 15 mA g... -1 Charge-discharge curves at current density;

[0034] Figure 12 To illustrate the application of the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 2 in Example 1, at 300 mA g...-1 Cyclic performance at current density;

[0035] Figure 13 To illustrate the application of the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 2 in Example 1, the sodium-ion battery was tested at 750 mA g. -1 Cyclic performance at current density;

[0036] Figure 14 To illustrate the application of the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 3 in Example 1, at 15 mA g... -1 Charge-discharge curves at current density;

[0037] Figure 15 To illustrate the application of the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 3 in Example 1, at 300 mA g... -1 Cyclic performance at current density;

[0038] Figure 16 To illustrate the application of the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 3 in Example 1, the sodium-ion battery was tested at 750 mA g. -1 Cyclic performance at current density;

[0039] Figure 17 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 2 was tested at 15 mA g. -1 Charge-discharge curves at current density;

[0040] Figure 18 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 2 was tested at 300 mA g. -1 Cyclic performance at current density;

[0041] Figure 19 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 3 was tested at 15 mA g. -1 Charge-discharge curves at current density;

[0042] Figure 20 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 3 was tested at 300 mA g. -1 Cyclic performance at current density;

[0043] Figure 21 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 3 was tested at 750 mA g. -1 Cyclic performance at current density;

[0044] Figure 22The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 4 was tested at 15 mA g. -1 Charge-discharge curves at current density;

[0045] Figure 23 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 4 was tested at 300 mA g. -1 Cyclic performance at current density;

[0046] Figure 24 The sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 4 was tested at 750 mA g. -1 Cyclic performance at current density;

[0047] Figure 25 The water contact angle of the positive electrode sheet prepared using the highly air-stable sodium-ion battery layered oxide positive electrode material of Example 1 as the positive electrode material;

[0048] Figure 26 The water contact angle of the positive electrode sheet prepared using the sodium-ion battery positive electrode material of Comparative Example 1 as the positive electrode material;

[0049] Figure 27 The XRD patterns of the highly air-stable sodium-ion battery layered oxide cathode material of Example 1 after standing in an air environment at 25°C and 50% relative humidity for 0 hours, 12 hours, 24 hours and 48 hours.

[0050] Figure 28 The XRD patterns of the sodium-ion battery cathode material of Comparative Example 1 after being left to stand in an air environment at a temperature of 25°C and a relative humidity of 50% for 0 hours, 12 hours, 24 hours and 48 hours.

[0051] Figure 29 SEM was performed on the highly air-stable sodium-ion battery layered oxide cathode material of Example 1, which was left to stand in an air environment at 25°C and 50% relative humidity for 48 hours.

[0052] Figure 30 SEM was performed on the sodium-ion battery cathode material of Comparative Example 1 after it had been left to stand in an air environment at 25°C and 50% relative humidity for 48 hours.

[0053] Figure 31 The charge-discharge curve of the sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 after aging for t hours is shown in Application Example 2.

[0054] Figure 32 The charge-discharge curve of the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1 after aging for t hours is shown in Application Example 2.

[0055] Figure 33 The charge-discharge curves of the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 2 after aging for t hours are shown in Application Example 2. Detailed Implementation

[0056] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0057] In this invention, 1C = 150mA g -1 .

[0058] Battery performance testing was conducted using the Blue Battery Testing System CT3002A; the test voltage range was 2V to 4V.

[0059] The nickel-iron-manganese hydroxide was purchased from GEM Co., Ltd., model S-3350A, battery grade.

[0060] Examples 1-3

[0061] A method for modifying the surface of a layered oxide cathode material for sodium-ion batteries by acid etching-induced surface reconstruction includes the following steps:

[0062] Step 1: Sodium carbonate (Na₂CO₃) and nickel-iron-manganese hydroxide are mixed and hand-ground in a mortar for 1 hour until homogeneous to obtain a first mixture. The first mixture is then kept at 900°C in a muffle furnace for 12 hours in air. After cooling to room temperature, it is hand-ground in a mortar for 1 hour to obtain a sodium-based crystalline oxide matrix material. The ratio of sodium carbonate to nickel-iron-manganese hydroxide by molar ratio is 1.05:1. The structural formula of nickel-iron-manganese hydroxide is Ni… 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂, the structural formula of the sodium-based crystalline oxide host material is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2;

[0063] Step 2: Mix the sodium-based morphological oxide host material and the modification solution, and etch it for 1 hour at room temperature and under ultrasonic (frequency 40kHz) conditions. Wash it three times with anhydrous ethanol, and obtain a solid powder after solid-liquid separation. Dry the solid powder at 120℃ for 3 hours to obtain a second mixture. The modification solution includes a solute and a solvent. The solute is acetic acid, and the solvent is anhydrous ethanol. The concentration of the solute in the modification solution is XM. The ratio of the mass fraction of the sodium-based morphological oxide host material to the volume fraction of the modification solution is 1:500. The unit of mass fraction is g, and the unit of volume fraction is mL. The value of X is shown in Table 1.

[0064] Step 3: Grind the second mixture (by hand in a mortar for 1 hour) into powder, place it in a muffle furnace, heat it to 450°C at a rate of 10 °C / min in an air atmosphere, hold it at 450°C for 5 hours, and cool it to room temperature to obtain a highly air-stable layered oxide cathode material for sodium-ion batteries.

[0065] Table 1

[0066]

[0067] Comparative Example 1

[0068] A method for preparing a sodium-ion battery cathode material includes: mixing sodium carbonate (Na2CO3) and nickel-iron-manganese hydroxide (Ni... 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂) Mix and hand-grind in a mortar for 1 hour until homogeneous to obtain the first mixture. In an air atmosphere, heat the first mixture in a muffle furnace at 900°C for 12 hours, cool to room temperature, and hand-grind in a mortar for 1 hour to obtain the sodium-based morphological oxide matrix material (NaNi). 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used as the positive electrode material for sodium-ion batteries, wherein the ratio of sodium carbonate to nickel iron manganese hydroxide by molar amount is 1.05:1.

[0069] Comparative Example 2

[0070] A method for preparing a sodium-ion battery cathode material includes the following steps:

[0071] Step 1, the nickel-iron-manganese hydroxide (Ni) from Example 1 is... 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2) and the modified solution (the same as the modified solution in Example 1) were mixed and etched at room temperature and ultrasonically (frequency 40 kHz) for 1 hour. After washing with anhydrous ethanol three times, solid powder was obtained after solid-liquid separation. The solid powder was dried at 120°C for 3 hours to obtain the first reactant. The mass ratio of nickel-iron-manganese hydroxide to the volume ratio of the modified solution was 1:500. The mass ratio is in g and the volume ratio is in mL.

[0072] Step 2: Grind the first reactant (by hand in a mortar for 1 hour) into powder, place it in a muffle furnace, heat it to 450°C at a rate of 10 °C / min in an air atmosphere, and hold it at 450°C for 5 hours. Cool it to room temperature to obtain the second reactant (modified nickel-iron-manganese hydroxide).

[0073] Step 3: Mix sodium carbonate (Na2CO3) and the second reactant, and hand-grind in a mortar for 1 hour until homogeneous. Then, keep it in a muffle furnace at 900°C for 12 hours in an air atmosphere. After cooling to room temperature, hand-grind in a mortar for 1 hour to obtain the sodium-ion battery cathode material.

[0074] Comparative Example 3

[0075] A method for preparing a sodium-ion battery cathode material is basically the same as that in Example 1, except that "acetic acid" is replaced with "citric acid".

[0076] Comparative Example 4

[0077] A method for preparing a sodium-ion battery cathode material is basically the same as that in Example 1, except that "acetic acid" is replaced with "oxalic acid".

[0078] The X-ray diffraction (XRD) patterns of the highly air-stable layered oxide cathode materials for sodium-ion batteries prepared in Examples 1-3 are shown below. Figure 1 As shown, the X-ray diffraction (XRD) patterns of the sodium-ion battery cathode materials prepared in Comparative Examples 1-4 are as follows: Figure 2 As shown, Figure 1 and Figure 2 PDF#25-0819 is the standard card for the O3 phase. (Source: [Insert PDF here]) Figure 1 and Figure 2 It can be seen that the high air-stable layered oxide cathode materials for sodium-ion batteries prepared in Examples 1-3 and the sodium-ion battery cathode materials prepared in Comparative Examples 1-4 both have a pure O3 phase (R3m) structure, good crystallinity, and Figure 1 The diffraction peaks of the (003) crystal plane at around 16.8° did not shift, indicating that the crystal framework did not change after acid etching, the interlayer spacing did not change, and no impurities were generated.

[0079] The scanning electron microscope (SEM) image of the highly air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 is shown below. Figure 3 As shown, the scanning electron microscope (SEM) image of the sodium-ion battery cathode material prepared in Comparative Example 1 is as follows. Figure 5 As shown, by Figure 3 and Figure 5It can be clearly observed that the air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 and the cathode material for sodium-ion batteries prepared in Comparative Example 1 both exhibit a spherical stacking morphology with a typical particle size of about 10 μm. The cathode material for sodium-ion batteries prepared in Comparative Example 1 has a high surface roughness and a large number of nipple-like protrusions. This type of structure is usually considered to be alkaline residue. The air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 exhibits extremely high surface smoothness, which indicates that the alkaline residue on its surface has been effectively removed.

[0080] The effect of acetic acid etching on the crystal surface structure was further investigated using high-resolution transmission electron microscopy (HRTEM). The edge portion of the highly air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 is shown in the HRTEM image. Figure 4 As shown, the high-resolution transmission electron microscope (HRTEM) image of the edge portion of the sodium-ion battery cathode material prepared in Comparative Example 1 is as follows. Figure 6 As shown ( Figure 6 The dashed line serves as the dividing line, with the edge of the sodium-ion battery positive electrode material to the right of the dashed line (and the back surface to the left of the dashed line)). Figure 4 and Figure 6 It can be clearly observed that both the air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 and the cathode material for sodium-ion batteries prepared in Comparative Example 1 exhibit clear and consistent lattice fringes, which correspond to the (003) crystal plane. The interlayer spacing of both the air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 and the cathode material for sodium-ion batteries prepared in Comparative Example 1 is 0.53 nm. This characterization result is consistent with... Figure 1 The crystal structure analysis results shown are consistent; compared with Comparative Example 1, the edges of the highly air-stable layered oxide cathode material for sodium-ion batteries prepared in Example 1 exhibit significant structural reconstruction, with the surface layer (thickness approximately 5-8 nm) showing a clear structural reconstruction phenomenon. Figure 4 The lattice fringes in the area (selected by the dashed line in the middle) become blurred and gradually evolve into an amorphous layer, while the internal region still maintains a good layered ordered structure.

[0081] The material was placed in an air environment with a temperature of 25°C and a relative humidity of 50% for 48 hours, and the result was obtained at hour 0 ( Figure 27 and Figure 28 (Pristine) 12 hours Figure 27 and Figure 28 "Air exposed for 12 hours" and 24 hours ( Figure 27 and Figure 28 "Air exposed 24h" and 48 hours ( Figure 27 and Figure 28Samples were taken from the "Air exposed 48h") and XRD tests were conducted. The material was one of the highly air-stable sodium-ion battery layered oxide cathode materials prepared in Example 1 and the sodium-ion battery cathode materials prepared in Comparative Example 1. Based on the highly air-stable sodium-ion battery layered oxide cathode materials prepared in Example 1, Figure 27 the XRD pattern shown was obtained. Based on the sodium-ion battery cathode materials prepared in Comparative Example 1, Figure 28 the XRD pattern shown was obtained. Figure 27 And Figure 28 in, PDF#25-0819 is the standard card for the O3 phase. In Figure 27 and Figure 28 "Sodium salt" represents sodium salts (during the air exposure of the material, side reactions occur with H2O and CO2 in the air to form sodium salts). In Figure 28 "Monoclinic O′3" represents the O′3-type monoclinic phase. As can be seen from Figure 28 when the sodium-ion battery cathode material prepared in Comparative Example 1 was exposed to this environment for 12 hours, there was no obvious change in the XRD pattern and the surface structure was intact. When exposed for 24 hours, an obvious O'3-type monoclinic phase appeared at about 16°. When the exposure time in air reached 48 hours, its structure completely collapsed and the characteristic diffraction peak intensity of the original O3 phase was significantly weakened to be hardly recognizable. As can be seen from Figure 27 in the XRD pattern of the highly air-stable sodium-ion battery layered oxide cathode material prepared in Example 1 of the present invention, there was no obvious change in the peak position. Even when exposed to air for 48 hours, only a small amount of Na salts could be observed. The above test results show that the highly air-stable sodium-ion battery layered oxide cathode material prepared in Example 1 of the present invention can significantly inhibit the formation of impurity phases during its exposure in air and effectively improve the air stability.

[0082] The highly air-stable sodium-ion battery layered oxide cathode material prepared in Example 1, which was placed in an air environment at a temperature of 25°C and a relative humidity of 50% for 48 hours, was subjected to morphological characterization. The obtained SEM is as shown in Figure 29 The sodium-ion battery cathode material prepared in Comparative Example 1, which was placed in an air environment at a temperature of 25°C and a relative humidity of 50% for 48 hours, was subjected to morphological characterization. The obtained SEM is as shown in Figure 30 The test results showed that after 48 hours of air exposure, a large number of scaly and fragmented impurities were visible on the surface of the sodium-ion battery cathode material of Comparative Example 1 ( Figure 30(Exemplary markings in the middle circle) Adhesion occurs, resulting in significant deterioration of the surface morphology. The highly air-stable sodium-ion battery layered oxide cathode material prepared in Example 1 showed no obvious impurity adhesion or morphological damage on its surface. This indicates that the highly air-stable sodium-ion battery layered oxide cathode material prepared in Example 1 of this invention exhibits significantly suppressed formation of sodium salts (mainly sodium carbonate) during air exposure, effectively improving the material's air stability and storage reliability.

[0083] Application Example 1

[0084] A method for preparing a sodium-ion battery (CR2032 standard coin cell) includes: assembling a positive electrode, a separator (separator wetted with electrolyte), and a negative electrode in the order of positive electrode, electrolyte, and negative electrode in an argon-atmosphere glove box. The negative electrode is a 12 mm diameter metallic sodium sheet, and the separator is a 19 mm diameter glass fiber membrane (Whatman, GF / A). The electrolyte includes sodium perchlorate (NaClO4), fluoroethylene carbonate (FEC), and propylene carbonate (PC). The concentration of sodium perchlorate in the electrolyte is 1.0 mol / L, and the concentration of fluoroethylene carbonate (FEC) in the electrolyte is 5 wt%. A method for obtaining the positive electrode includes: mixing positive electrode material, conductive carbon black (Super P), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone until homogeneous. The mass fractions of the positive electrode material, conductive carbon black (Super P), and N-methylpyrrolidone are specified. The mass ratio of P), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (N-methylpyrrolidone) was 80:10:10:0.5, with mass parts in mg and volume parts in mL, to obtain a positive electrode slurry. This slurry was coated onto a current collector (aluminum foil) and dried in a 120°C oven for 12 hours. The slurry was then cut into 10mm diameter electrodes, with a positive electrode material loading of 2 mg on each 10mm diameter electrode. The positive electrode material was one of the high-air-stable layered oxide positive electrode materials for sodium-ion batteries prepared in Examples 1-3 and Comparative Examples 1-4, respectively. The corresponding sodium-ion batteries were obtained from Examples 1-3 and Comparative Examples 1-4.

[0085] The positive electrode sheet prepared using the highly air-stable sodium-ion battery layered oxide positive electrode material from Example 1 as the positive electrode material was subjected to water contact angle (WCA) testing, and the results are as follows: Figure 25 As shown, the positive electrode sheet prepared using the sodium-ion battery positive electrode material of Comparative Example 1 as the positive electrode material was subjected to water contact angle (WCA) testing, and the results are as follows. Figure 26 As shown, by Figure 25 and Figure 26It can be seen that the water contact angle of the positive electrode sheet corresponding to Example 1 is 131±2°, while the water contact angle of the positive electrode sheet corresponding to Comparative Example 1 is 94±2°. Compared with Comparative Example 1, the positive electrode sheet prepared by using the highly air-stable sodium-ion battery layered oxide positive electrode material of Example 1 as the positive electrode material has better hydrophobicity, and the improvement in hydrophobicity indicates a significant enhancement in air stability.

[0086] At a current density of 15 mA g -1 At that time, charge-discharge tests were conducted on the sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1. The test results are as follows: Figure 7 As shown. By Figure 7 It can be seen that the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 1 can achieve an initial discharge specific capacity of 132.4 mAh g⁻¹. -1 The initial coulombic efficiency is approximately 100%; the initial discharge capacity of the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1 can reach 137.5 mAh g⁻¹. -1 The initial coulombic efficiency is approximately 95%. This invention has higher coulombic efficiency and higher capacity utilization.

[0087] At a current density of 300 mA g -1 Cycle performance tests were conducted on the sodium-ion battery prepared using the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared using the sodium-ion battery cathode material of Comparative Example 1. The test results are as follows: Figure 8 As shown.

[0088] At a current density of 750 mA g -1 Cycle performance tests were conducted on the sodium-ion battery prepared using the high air-stable layered oxide cathode material of Example 1 and the sodium-ion battery prepared using the sodium-ion battery cathode material of Comparative Example 1. The test results are as follows: Figure 9 As shown.

[0089] Discharge tests were conducted at different current densities on sodium-ion batteries prepared using the highly air-stable layered oxide cathode material of Example 1 and sodium-ion batteries prepared using the cathode material of Comparative Example 1, respectively, and the results were as follows: Figure 10 The rate performance diagram is shown. It illustrates 5 cycles at each current density, with one discharge specific capacity obtained per cycle. The current density increases from 0.5C, 1C, 2C, 5C to 10C, then sequentially decreases back to 5C, 2C, 1C, and 0.5C. Figure 10It can be seen that the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 1 has a discharge specific capacity (average value) of 118.8, 110.9, 107.8, 95.3 and 68.2 mAh g for current densities increasing from 0.5C, 1C, 2C, 5C to 10C, respectively. -1 The sodium-ion batteries prepared using the sodium-ion battery cathode material of Comparative Example 1 had discharge specific capacities (average values) of 131, 124.3, 110.6, 83.1, and 52.9 mAh g for current densities increasing from 0.5C, 1C, 2C, 5C to 10C, respectively. -1 The sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 1 exhibits a significantly better discharge specific capacity than Comparative Example 1 at high current densities, demonstrating excellent rate performance. This is because the amorphous layer formed after acetic acid etching contains many sodium vacancies, which accelerates the diffusion kinetics of sodium ions. In addition, acetic acid etching removes residual alkali on the surface, which significantly reduces interfacial impedance. Under the combined influence of these two factors, Example 1 demonstrates excellent rate performance at high current densities.

[0090] At a current density of 15 mA g -1 At that time, a charge-discharge test was conducted on the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 2. The test results are as follows: Figure 11 As shown. At a current density of 300 mAg -1 Then, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 2 was subjected to cycle performance testing, and the test results are as follows: Figure 12 As shown. At a current density of 750 mA g -1 Then, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 2 was subjected to cycle performance testing, and the test results are as follows: Figure 13 As shown.

[0091] At a current density of 15 mA g -1 At that time, a charge-discharge test was conducted on the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 3. The test results are as follows: Figure 14 As shown. At a current density of 300 mAg -1 Then, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 3 was subjected to cycle performance testing, and the test results are as follows: Figure 15 As shown. At a current density of 750 mA g -1 Then, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 3 was subjected to cycle performance testing, and the test results are as follows: Figure 16As shown.

[0092] At a current density of 15 mA g -1 At that time, a charge-discharge test was conducted on the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 2, and the test results are as follows. Figure 17 As shown. At a current density of 300 mA g -1 Then, the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 2 was subjected to cycle performance testing, and the test results are as follows: Figure 18 As shown.

[0093] At a current density of 15 mA g -1 At that time, a charge-discharge test was conducted on the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 3, and the test results are as follows. Figure 19 As shown. At a current density of 300 mA g -1 Then, the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 3 was subjected to cycle performance testing, and the test results are as follows: Figure 20 As shown. At a current density of 750 mA g -1 Then, the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 3 was subjected to cycle performance testing, and the test results are as follows: Figure 21 As shown.

[0094] At a current density of 15 mA g -1 At that time, charge-discharge tests were conducted on the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 4, and the test results are as follows. Figure 22 As shown. At a current density of 300 mA g -1 Then, the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 4 was subjected to cycle performance testing, and the test results are as follows: Figure 23 As shown. At a current density of 750 mA g -1 Then, the sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 4 was subjected to cycle performance testing, and the test results are as follows: Figure 24 As shown.

[0095] The charge-discharge test data of sodium-ion batteries prepared from the high air-stable layered oxide cathode materials of Examples 1-3 and sodium-ion batteries prepared from the cathode materials of Comparative Examples 1-4 are summarized in Table 2.

[0096] Table 2

[0097]

[0098] Cycle performance test data (current density 300 mA g) of sodium-ion batteries prepared from the high air-stable layered oxide cathode materials of Examples 1-3 and sodium-ion batteries prepared from the cathode materials of Comparative Examples 1-4. -1 The results are summarized in Table 3.

[0099] Table 3

[0100]

[0101] Cycle performance test data (current density 750 mA g) of sodium-ion batteries prepared from the high air-stable layered oxide cathode materials of Examples 1-3 and sodium-ion batteries prepared from the cathode materials of Comparative Examples 1 and 3-4. -1 The results are summarized in Table 4.

[0102] Table 4

[0103]

[0104] As can be seen from the test results in Tables 2-4, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 1 has the best cycle stability.

[0105] Application Example 2

[0106] The material was aged for t hours and then used as the positive electrode material. Referring to the "Method for Preparing a Sodium-ion Battery (CR2032 Standard Button Battery)" in Application Example 1, a sodium-ion battery was prepared from the material aged for t hours. The material was one of the high air-stable sodium-ion battery layered oxide positive electrode material prepared in Example 1, or the sodium-ion battery positive electrode material prepared in Comparative Example 1 and Comparative Example 2. The t values ​​were one of 0, 12, 24, and 48 hours. The aging conditions were: standing in an air environment with a temperature of 25°C and a humidity of 50%.

[0107] Sodium-ion batteries prepared from the high air-stable layered oxide cathode material of Example 1 after aging for t hours, sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 1 after aging for t hours, and sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 2 after aging for t hours were subjected to charge-discharge tests. At 15 mA g -1 Below is a charge-discharge curve of a sodium-ion battery prepared from the high air-stable layered oxide cathode material of Example 1 after aging for t hours. Figure 31 As shown ( Figure 31In the examples "Example 1", "Example 1 - Air exposed 12h", "Example 1 - Air exposed 24h", and "Example 1 - Air exposed 48h", they respectively represent sodium-ion batteries prepared from high-air-stable layered oxide cathode materials for sodium-ion batteries after 0 hours of aging, sodium-ion batteries prepared from high-air-stable layered oxide cathode materials for sodium-ion batteries after 12 hours of aging, sodium-ion batteries prepared from high-air-stable layered oxide cathode materials for sodium-ion batteries after 24 hours of aging, and sodium-ion batteries prepared from high-air-stable layered oxide cathode materials for sodium-ion batteries after 48 hours of aging, at 15 mA g. -1 Below is a charge-discharge curve of a sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 1 after aging for t hours. Figure 32 As shown ( Figure 32 In the figures, “Comparative Example 1,” “Comparative Example 1-Air exposed 12h,” “Comparative Example 1-Air exposed 24h,” and “Comparative Example 1-Air exposed 48h” represent sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 1 after 0 hours of aging, sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 1 after 12 hours of aging, sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 1 after 24 hours of aging, and sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 1 after 48 hours of aging, respectively, at 15 mA g. -1 Below is a charge-discharge curve of a sodium-ion battery prepared from the sodium-ion battery cathode material of Comparative Example 2 after aging for t hours. Figure 33 As shown ( Figure 33 In the figures, "Comparative Example 2", "Comparative Example 2 - Air exposed 12h", "Comparative Example 2 - Air exposed 24h", and "Comparative Example 2 - Air exposed 48h" represent sodium-ion batteries prepared from the sodium-ion battery cathode material of Comparative Example 2 after 0 hours of aging, after 12 hours of aging, after 24 hours of aging, and after 48 hours of aging, respectively. (15mA g) -1At t=0, the initial discharge specific capacity of Example 1, Comparative Example 1 and Comparative Example 2 is shown in Table 5; at t=12, the initial discharge specific capacity of Example 1, Comparative Example 1 and Comparative Example 2 is shown in Table 6; at t=24, the initial discharge specific capacity of Example 1, Comparative Example 1 and Comparative Example 2 is shown in Table 7; at t=48, the initial discharge specific capacity of Example 1, Comparative Example 1 and Comparative Example 2 is shown in Table 8.

[0108] Table 5

[0109]

[0110] Table 6

[0111]

[0112] Table 7

[0113]

[0114] Table 8

[0115]

[0116] Depend on Figures 31-33 As shown in Tables 5-8, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 1 exhibits the best air stability. Comparing Example 1 and Comparative Example 1, it is evident that when placed in an air environment at 25°C and 50% relative humidity for the same period, the sodium-ion battery prepared from the highly air-stable layered oxide cathode material of Example 1 performs better than that of Comparative Example 1. This demonstrates that modifying the sodium-based layered oxide substrate with a modification solution is crucial for improving the material's air stability. Furthermore, in Comparative Example 2, nickel-iron-manganese hydroxide (Ni... 1 / 3 Fe 1 / 3 Mn 1 / 3 Mixing (OH)₂ with the modified solution cannot achieve the technical effect of this invention. Only under the technical solution of this invention can a highly air-stable layered oxide cathode material for sodium-ion batteries be prepared, thereby obtaining a high-performance sodium-ion battery.

[0117] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for modifying the surface of a layered oxide cathode material for sodium-ion batteries by acid etching-induced surface reconstruction, characterized in that, Includes the following steps: Step 1: Mix sodium carbonate and nickel-iron-manganese hydroxide until homogeneous to obtain a first mixture. In an air atmosphere, maintain the first mixture at 800-1000℃ for 10-15 hours, then cool to room temperature to obtain a sodium-based layered oxide matrix material. The ratio of sodium carbonate to nickel-iron-manganese hydroxide by molar amount is (1-1.08):

1. The structural formula of the nickel-iron-manganese hydroxide is Ni... 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2; Step 2: Mix the sodium-based crystalline oxide substrate material and the modification solution, etch for 0.5 to 2 hours, wash, and dry to obtain a second mixture. The modification solution includes a solute and a solvent. The solute is acetic acid, and the concentration of the solute in the modification solution is 0.1 to 0.9 M. Step 3: Grind the second mixture into powder, keep it at 350~650°C for 3~10 hours in an air atmosphere, and cool it to room temperature to obtain the sodium-ion battery layered oxide cathode material.

2. The modification method according to claim 1, characterized in that, In step 2, the ratio of the mass fraction of the sodium-based crystalline oxide substrate to the volume fraction of the modified solution is 1:(100~500), with the mass fraction in g and the volume fraction in mL.

3. The modification method according to claim 1, characterized in that, In step 2, the sodium-based crystalline oxide substrate material and the modified solution are mixed and etched at room temperature and under ultrasonic conditions for 0.5 to 2 hours.

4. The modification method according to claim 1, characterized in that, In step 2, the solvent is an alcohol solvent.

5. The modification method according to claim 4, characterized in that, The alcohol solvent is at least one of anhydrous ethanol and ethylene glycol.

6. The modification method according to claim 1, characterized in that, In step 3, the heating rate to 350~650°C is 5~10 °C / min.

7. A highly air-stable layered oxide cathode material for sodium-ion batteries obtained by the modification method according to any one of claims 1 to 6.

8. A sodium-ion battery, comprising: High-altitude air-stable layered oxide cathode material for sodium-ion batteries.

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