Single-crystal double-phase sodium-ion battery layered positive electrode material and preparation method and application thereof

Abstract

The invention discloses a single-crystal double-phase sodium ion battery layered positive electrode material and a preparation method and application thereof, the method comprises the following steps: step 1, dissolving Ni (CH3COO) 2.4 H2O, Mn (CH3COO) 3.2 H2O and CH3COONa in a mixed solvent of deionized water and absolute ethyl alcohol, then adding citric acid, and stirring to obtain a green turbid complexing solution; step 2, firstly dropwise adding ammonia water into the complexing solution, adjusting the pH value to 8, then transferring the complexing solution into a constant-temperature water bath, stirring to be gel-shaped, and then sequentially drying and grinding to obtain precursor powder; and step 3, putting the precursor powder into a muffle furnace, pre-calcining in an air atmosphere at 450-500 DEG C for 5 hours, cooling, grinding, continuously putting into the muffle furnace, sintering at 900-950 DEG C for 10 hours, and cooling to room temperature, thereby obtaining the O3 / P2 composite phase NaNi0. 5Mn0. 5O2 material. According to the invention, the capacity, thermal stability and cycle performance of the sodium ion battery are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically a single-crystal dual-phase sodium-ion battery layered cathode material, its preparation method, and its application. Background Technology

[0002] In recent years, sodium-ion batteries have been widely considered one of the most promising large-scale energy storage systems due to their abundant resources, low cost, and high safety. However, developing cathode materials that combine high capacity and long cycle life still faces significant challenges. Layered transition metal oxides (such as NaNi) 0.5 Mn 0.5 O2 is considered an ideal candidate material due to its high specific capacity and good electronic conductivity. However, the single O3 phase is prone to irreversible phase transition and lattice collapse during charge and discharge, resulting in rapid capacity decay and insufficient cycle stability. In addition, the solid-state method or sol-gel method commonly used in the synthesis of layered transition metal oxides is often accompanied by uneven metal ion dispersion and excessive organic residues, which limits the control of phase structure and further weakens the thermal stability and electrochemical performance of the material. Therefore, it is particularly necessary to develop new synthesis strategies. Summary of the Invention

[0003] The purpose of this invention is to provide a single-crystal dual-phase layered cathode material for sodium-ion batteries, its preparation method, and its application. The prepared cathode material is a single-crystal O3 / P2 dual-phase material, which effectively improves capacity, thermal stability, and cycle performance.

[0004] This invention is achieved through the following technical solution: A method for preparing a single-crystal dual-phase sodium-ion battery layered cathode material includes the following steps: Step 1: Weigh out 2.5 mmol Ni(CH3COO)2·4H2O, 2.5 mmol Mn(CH3COO)3·2H2O and 5 mmol CH3COONa respectively, and set aside. Step 2: Dissolve Ni(CH3COO)2·4H2O, Mn(CH3COO)3·2H2O and CH3COONa in a mixed solvent of deionized water and anhydrous ethanol, then add 10 mmol of citric acid and stir to obtain a green turbid complex solution. Step 3: First, add ammonia water to the complexation solution to adjust the pH to 8. Then, transfer the complexation solution to a constant temperature water bath at 70~90℃ and stir until it becomes gel-like. Next, dry and grind it in sequence to obtain the precursor powder. Step 4: Place the precursor powder into a muffle furnace and pre-calcine it at 450-500℃ for 5 hours in an air atmosphere. After cooling, grind it and continue to place it into the muffle furnace for sintering at 900-950℃ for 10 hours. Cool to room temperature to obtain the O3 / P2 composite phase NaNi.0.5 Mn 0.5 O2 materials.

[0005] Furthermore, the stirring in step 2 is performed at a speed of 450 rpm using magnetic stirring for 12 hours.

[0006] Furthermore, in step 2, the mixed solvent of deionized water and anhydrous ethanol is prepared by mixing 50 mL of deionized water and 30 mL of anhydrous ethanol.

[0007] Furthermore, the concentration of ammonia in step 3 is 25%.

[0008] Furthermore, in step 3, the stirring is performed at a speed of 200 rpm using magnetic stirring until a gel-like state is reached.

[0009] Furthermore, the drying in step 3 is carried out in a vacuum oven at 80°C for 12 hours.

[0010] Furthermore, the grinding time in steps 3 and 4 is 10 to 30 minutes.

[0011] A layered cathode material for monocrystalline dual-phase sodium-ion batteries.

[0012] The application of a single-crystal biphase layered cathode material in sodium-ion batteries includes the following steps: Step 1: Mix the positive electrode material, conductive agent and PVDF solution evenly according to the mass ratio of 8:1:1 to make a slurry. The PVDF solution is made by mixing PVDF and N-methylpyrrolidone in a mass ratio of 4:96. Step 2: Coat the slurry onto aluminum foil, dry it, and then hot roll it to produce a sodium-ion battery positive electrode sheet.

[0013] Furthermore, the conductive agent is Super-P or acetylene black.

[0014] The present invention has the following beneficial technical effects: 1) This invention uses a water-alcohol mixed solvent to regulate the distribution and complexation state of metal ions in the precursor, achieving the synergistic evolution of the O3 and P2 phases during calcination. This forms an ordered dual-phase structure within the single-crystal particles, resulting in a single-crystal O3 / P2 mixed-phase cathode material with a continuous lattice and stable interface. This reduces the structural stress of the single O3 phase, providing more favorable conditions for the stable formation of the P2 phase, improving the structural stability and electrochemical performance of the material, and achieving a balance between capacity retention and cycle life. This is attributed to the fact that the dual-phase structure of the O3 / P2 mixed-phase cathode material can effectively suppress interlayer slip and structural collapse during cycling, thereby significantly enhancing lattice stability and interface integrity, and improving the diffusion kinetics of sodium ions, thus improving the capacity retention and cycle life of the material.

[0015] 2) When the O3 / P2-NNMO material prepared in this invention is used as a positive electrode material for sodium-ion batteries, its initial discharge capacity can reach approximately 117.2 mAh g⁻¹ in the voltage range of 2.0V to 4V. -1 It maintains high reversible capacity at different rates from 0.2 to 5C, and after 100 cycles at a current density of 1C, the capacity can still be maintained at approximately 80.3 mAh g. -1 The capacity retention rate reached 75%, compared to existing materials O3-NNMO (NaNi). 0.5 Mn 0.5 For sodium-ion batteries assembled with O2, both the battery capacity and cycle performance are significantly improved, providing a new solution for the application of high-performance sodium-ion batteries. Attached Figure Description

[0016] Figure 1 XRD patterns of O3 / P2-NNMO prepared in Example 1 and O3-NNMO prepared in Comparative Example 1; Figure 2 SEM images of O3 / P2-NNMO prepared in Example 1; Figure 3 SEM images of O3-NNMO prepared in Comparative Example 1; Figure 4 The sodium-ion battery positive electrode sheets prepared in Example 1 and Comparative Example 1 were assembled into sodium-ion batteries, and the first charge-discharge curves were obtained at a current density of 0.1C within a voltage range of 2 V to 4 V. Figure 5 The sodium-ion battery positive electrode sheets prepared in Example 1 and Comparative Example 1 were assembled into sodium-ion batteries, and their rate performance in the voltage range of 2 V to 4 V was shown in the figure. Figure 6 The sodium-ion battery positive electrode sheets prepared in Example 1 and Comparative Example 1 were assembled into sodium-ion batteries, and the cycle life diagrams at 1C current density within the voltage range of 2 V to 4 V were obtained. Detailed Implementation

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

[0018] Example 1 Step 1: Weigh out 2.5 mmol of nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O), 2.5 mmol of manganese acetate tetrahydrate (Mn(CH3COO)3·2H2O), and 5 mmol of sodium acetate (CH3COONa) for later use; Step 2: First, mix 50 mL of deionized water and 30 mL of anhydrous ethanol to obtain a mixed solvent of deionized water and anhydrous ethanol. Then, dissolve Ni(CH3COO)2·4H2O, Mn(CH3COO)3·2H2O and CH3COONa in the mixed solvent of deionized water and anhydrous ethanol. Next, add 10 mmol of citric acid as a chelating agent and stir magnetically at 450 rpm for 12 h to obtain a green turbid complex solution. Step 3: First, add 25% ammonia water to the complexation solution to adjust the pH to 8. Then, transfer the complexation solution to a constant temperature water bath at 70°C and stir at 200 rpm until it becomes gel-like. Next, dry it in a vacuum oven at 80°C for 12 hours and then grind it for 10 minutes to obtain the precursor powder. Step 4: Place the precursor powder into a muffle furnace and pre-calcine it at 500℃ for 5 h in an air atmosphere. After cooling, grind it for 10 min, then place it back into the muffle furnace and sinter it at 900℃ for 10 h. Cool to room temperature to obtain the O3 / P2 composite phase NaNi. 0.5 Mn 0.5 O2 material, denoted as O3 / P2-NNMO; Step 5: Prepare the positive electrode sheet for the sodium-ion battery. The specific process is as follows: Step 5.1: Disperse PVDF in N-methylpyrrolidone at a mass ratio of 4:96, mix thoroughly to obtain a PVDF solution; Step 5.2: Mix O3 / P2-NNMO, Super-P and PVDF solutions evenly at a mass ratio of 8:1:1 to prepare a slurry; Step 5.3: Coat the slurry onto aluminum foil, dry it, and then hot roll it to produce a sodium-ion battery positive electrode sheet.

[0019] Example 2 Step 1: Weigh out 2.5 mmol of nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O), 2.5 mmol of manganese acetate tetrahydrate (Mn(CH3COO)3·2H2O), and 5 mmol of sodium acetate (CH3COONa) for later use; Step 2: First, mix 50 mL of deionized water and 30 mL of anhydrous ethanol to obtain a mixed solvent of deionized water and anhydrous ethanol. Then, dissolve Ni(CH3COO)2·4H2O, Mn(CH3COO)3·2H2O and CH3COONa in the mixed solvent of deionized water and anhydrous ethanol. Next, add 10 mmol of citric acid as a chelating agent and stir magnetically at 450 rpm for 12 h to obtain a green turbid complex solution. Step 3: First, add 25% ammonia water to the complexation solution to adjust the pH to 8. Then, transfer the complexation solution to a constant temperature water bath at 80°C and stir at 200 rpm until it becomes gel-like. Next, dry it in a vacuum oven at 80°C for 12 hours and then grind it for 20 minutes to obtain the precursor powder. Step 4: Place the precursor powder into a muffle furnace and pre-calcine it at 450℃ for 5 h in an air atmosphere. After cooling, grind it for 20 min, then place it back into the muffle furnace and sinter it at 925℃ for 10 h. Cool to room temperature to obtain the O3 / P2 composite phase NaNi. 0.5 Mn 0.5 O2 material, denoted as O3 / P2-NNMO; Step 5: Prepare the positive electrode sheet for the sodium-ion battery. The specific process is as follows: Step 5.1: Disperse PVDF in N-methylpyrrolidone at a mass ratio of 4:96, mix thoroughly to obtain a PVDF solution; Step 5.2: Mix O3 / P2-NNMO, acetylene black and PVDF solution evenly according to a mass ratio of 8:1:1 to prepare a slurry; Step 5.3: Coat the slurry onto aluminum foil, dry it, and then hot roll it to produce a sodium-ion battery positive electrode sheet.

[0020] Example 3 Step 1: Weigh out 2.5 mmol of nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O), 2.5 mmol of manganese acetate tetrahydrate (Mn(CH3COO)3·2H2O), and 5 mmol of sodium acetate (CH3COONa) for later use; Step 2: First, mix 50 mL of deionized water and 30 mL of anhydrous ethanol to obtain a mixed solvent of deionized water and anhydrous ethanol. Then, dissolve Ni(CH3COO)2·4H2O, Mn(CH3COO)3·2H2O and CH3COONa in the mixed solvent of deionized water and anhydrous ethanol. Next, add 10 mmol of citric acid as a chelating agent and stir magnetically at 450 rpm for 12 h to obtain a green turbid complex solution. Step 3: First, add 25% ammonia water to the complexation solution to adjust the pH to 8. Then, transfer the complexation solution to a constant temperature water bath at 90°C and stir at 200 rpm until it becomes gel-like. Next, dry it in a vacuum oven at 80°C for 12 hours and then grind it for 30 minutes to obtain the precursor powder. Step 4: Place the precursor powder into a muffle furnace and pre-calcine it at 475°C for 5 hours in air atmosphere. After cooling, grind it for 30 minutes, then place it back into the muffle furnace and sinter it at 950°C for 10 hours. Cool to room temperature to obtain the O3 / P2 composite phase NaNi. 0.5 Mn 0.5 O2 material, denoted as O3 / P2-NNMO; Step 5: Prepare the positive electrode sheet for the sodium-ion battery. The specific process is as follows: Step 5.1: Disperse PVDF in N-methylpyrrolidone at a mass ratio of 4:96, mix thoroughly to obtain a PVDF solution; Step 5.2: Mix O3 / P2-NNMO, acetylene black and PVDF solution evenly according to a mass ratio of 8:1:1 to prepare a slurry; Step 5.3: Coat the slurry onto aluminum foil, dry it, and then hot roll it to produce a sodium-ion battery positive electrode sheet.

[0021] Comparative Example 1 Step 1: Weigh out 2.5 mmol of nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O), 2.5 mmol of manganese acetate tetrahydrate (Mn(CH3COO)3·2H2O), and 5 mmol of sodium acetate (CH3COONa) for later use; Step 2: Dissolve Ni(CH3COO)2·4H2O, Mn(CH3COO)3·2H2O and CH3COONa in deionized water, then add 10 mmol of citric acid as a chelating agent, and stir magnetically at 450 rpm for 12 h to obtain a green turbid complex solution. Step 3: First, add ammonia water to the complexation solution to adjust the pH to 8. Then, transfer the complexation solution to a constant temperature water bath at 70°C and stir at 200 rpm until it becomes gel-like. Next, dry it in a vacuum oven at 80°C for 12 hours and then grind it for 10 minutes to obtain the precursor powder. Step 4: Place the precursor powder into a muffle furnace and pre-calcine it at 500°C for 5 hours in air atmosphere. After cooling, grind it for 10 minutes, then place it back into the muffle furnace and sinter it at 900°C for 10 hours. Cool to room temperature to obtain O3-type NaNi. 0.5 Mn 0.5 O2 (O3-NNMO) material, denoted as O3-NNMO; Step 5: Prepare the positive electrode sheet for the sodium-ion battery. The specific process is as follows: Step 5.1: Disperse PVDF in N-methylpyrrolidone at a mass ratio of 4:96, mix thoroughly to obtain a PVDF solution; Step 5.2: Mix O3-NNMO, acetylene black and PVDF solution evenly according to a mass ratio of 8:1:1 to prepare a slurry; Step 5.3: Coat the slurry onto aluminum foil, dry it, and then hot roll it to produce a sodium-ion battery positive electrode sheet.

[0022] from Figure 1 It can be seen that: the O3-type NaNi prepared in Comparative Example 1 0.5 Mn 0.5 The diffraction peaks of O2 material are sharp and clear, similar to those of O3-type NaNi. 0.5 Mn 0.5 It conforms to the standard XRD card of O2 (PDF#54-0887, space group R-3 m); the O3 / P2 composite phase NaNi prepared in Example 1 is consistent with the standard XRD card of O2 (PDF#54-0887, space group R-3 m); 0.5 Mn 0.5 The O2 material exhibits a new diffraction peak at 15.72°, located to the left of the (003) peak of the O3 phase, corresponding to the reflection from the (002) crystal plane of the P2 phase, similar to that of Na. 0.67 Ni 0.33 Mn 0.67 The results are consistent with the standard XRD card of O2 (PDF#54-0894, space group P63 / mmc), indicating that prolonged stirring in a mixed solvent of deionized water and anhydrous ethanol can induce a partial transformation of the O3 structure to the P2 phase, thereby obtaining an O3 / P2 biphase layered cathode material for sodium-ion batteries.

[0023] from Figure 3 It can be seen that the O3-NNMO prepared in Comparative Example 1 exhibits a typical aggregated porous bulk structure, with rough and irregular particle surfaces and a wide particle size distribution; from Figure 2 It can be seen that the O3 / P2-NNMO sample prepared in Example 1 exhibits highly consistent orientation and neat edges of hexagonal plate-like crystals, with a morphology tending towards single crystallization. It is precisely because the O3 / P2-NNMO prepared in Example 1 exhibits O3 / P2 dual phases and hexagonal plate-like crystals that it has excellent thermal stability, cycling stability, and high capacity.

[0024] The sodium-ion battery cathode sheets prepared in Comparative Example 1 and Example 1 were assembled into sodium-ion batteries, and the battery performance was tested. The results are shown in [reference needed]. Figures 4-6 : from Figure 4 It can be seen that the sodium-ion battery prepared using O3-NNMO as the positive electrode material in Comparative Example 1 exhibits a performance of 102.6 mAh·g at 0.1C. -1 The sodium-ion battery using the O3 / P2-NNMO material prepared in Example 1 as the positive electrode material exhibited a capacity of 117.2 mAh·g at 0.1C. -1The capacity; This describes the O3 / P2 composite phase NaNi prepared in Example 1. 0.5 Mn 0.5 O2 materials can effectively improve the capacity of sodium-ion batteries.

[0025] from Figure 5 It can be seen that, compared with the sodium-ion battery using O3-NNMO as the cathode material prepared in Comparative Example 1, the sodium-ion battery using O3 / P2-NNMO as the cathode material prepared in Example 1 exhibits stronger capacity retention in the range of 0.2~5 C, indicating that it has a better kinetic response.

[0026] from Figure 6 It can be seen that: the sodium-ion battery with O3-NNMO as the positive electrode material prepared in Comparative Example 1 retains 60% of its initial capacity after 100 cycles at 1 C; the sodium-ion battery with O3 / P2-NNMO as the positive electrode material prepared in Example 1 retains 75% of its initial capacity after 100 cycles at 1 C, indicating that it has a high capacity retention rate.

Claims

1. A method for preparing a single-crystal dual-phase sodium-ion battery layered cathode material, characterized in that, Includes the following steps: Step 1: Weigh out 2.5 mmol Ni(CH3COO)2·4H2O, 2.5 mmol Mn(CH3COO)3·2H2O and 5 mmol CH3COONa respectively, and set aside. Step 2: Dissolve Ni(CH3COO)2·4H2O, Mn(CH3COO)3·2H2O and CH3COONa in a mixed solvent of deionized water and anhydrous ethanol, then add 10 mmol of citric acid and stir to obtain a green turbid complex solution. Step 3: First, add ammonia water to the complexation solution to adjust the pH to 8. Then, transfer the complexation solution to a constant temperature water bath at 70~90℃ and stir until it becomes gel-like. Next, dry and grind it in sequence to obtain the precursor powder. Step 4: Place the precursor powder into a muffle furnace and pre-calcine it at 450-500℃ for 5 hours in an air atmosphere. After cooling, grind it and continue to place it into the muffle furnace for sintering at 900-950℃ for 10 hours. Cool to room temperature to obtain the O3 / P2 composite phase NaNi. 0.5 Mn 0.5 O2 materials.

2. The method for preparing the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 1, characterized in that, The stirring in step 2 is performed at a speed of 450 rpm using magnetic stirring for 12 hours.

3. The method for preparing the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 1, characterized in that, In step 2, the mixed solvent of deionized water and anhydrous ethanol is prepared by mixing 50 mL of deionized water and 30 mL of anhydrous ethanol.

4. The method for preparing the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 1, characterized in that, The concentration of ammonia in step 3 is 25%.

5. The method for preparing the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 1, characterized in that, The stirring in step 3 is performed at a speed of 200 rpm using magnetic stirring until a gel-like consistency is reached.

6. The method for preparing the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 1, characterized in that, The drying in step 3 is carried out in a vacuum oven at 80°C for 12 hours.

7. The method for preparing the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 1, characterized in that, The grinding time for steps 3 and 4 is 10 to 30 minutes.

8. A single-crystal biphase sodium-ion battery layered cathode material prepared by the method according to any one of claims 1 to 7.

9. The application of the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 8 in sodium-ion batteries, characterized in that, Includes the following steps: Step 1: Mix the positive electrode material, conductive agent and PVDF solution evenly according to the mass ratio of 8:1:1 to make a slurry. The PVDF solution is made by mixing PVDF and N-methylpyrrolidone in a mass ratio of 4:

96. Step 2: Coat the slurry onto aluminum foil, dry it, and then hot roll it to produce a sodium-ion battery positive electrode sheet.

10. The application of the single-crystal dual-phase sodium-ion battery layered cathode material according to claim 9 in sodium-ion batteries, characterized in that, The conductive agent is Super-P or acetylene black.

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