Preparation method of a double-site co-doped sodium-ion battery cathode material

Abstract

The application belongs to the technical field of sodium ion batteries, and discloses a preparation method of a double-site co-doped sodium ion battery positive electrode material. The method comprises the following steps: (1) according to the molar ratio of each metal element in the chemical formula of the target product, corresponding metal salts are weighed and dissolved in an ethanol solution to obtain a metal salt solution; oxalic acid is dissolved in an ethanol solution to obtain an oxalic acid solution; (2) under ultrasonic conditions, the metal salt solution is added dropwise into the oxalic acid solution, and stirring is continuously performed; after the metal salt solution is completely added dropwise, ultrasonic treatment is continuously performed; the suspension treated by ultrasonic treatment is placed in an oven for drying, and the powder obtained by drying is ground; (3) the ground powder is placed in a corundum box and then placed in a tube furnace for sintering; first, heating is performed to 500 DEG C for heat preservation; after cooling, the tablet is taken out, the pressed tablet is continuously placed in the tube furnace, heating is performed to 900 DEG C for heat preservation, after cooling, the tablet is taken out and ground, and the target product is obtained.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a method for preparing a dual-site co-doped sodium-ion battery cathode material. Background Technology

[0002] Since the beginning of the 21st century, human demand for energy has increased significantly. However, the depletion of traditional fossil fuels and the environmental pollution caused by their use have forced people to seek new clean energy sources. Currently, clean energy mainly consists of solar and wind power, which are largely intermittent and unpredictable, and highly susceptible to environmental influences. To better utilize these energy sources, energy storage devices are needed to store excess energy during off-peak hours and transmit it through the power grid when needed, achieving peak shaving and valley filling. Currently, the most widely used rechargeable battery is the lithium-ion battery. However, due to the scarcity and uneven distribution of lithium resources, and the soaring lithium prices in recent years, the development of lithium batteries has been severely hampered. Sodium-ion batteries, on the other hand, have a similar principle to lithium batteries, and sodium is abundant, widely distributed, and low-cost, making them a promising next-generation energy storage device.

[0003] Currently, sodium-ion battery cathode materials are classified into four categories: Prussian blue compounds, polyanionic compounds, organic materials, and layered transition metal oxides. Layered transition metal oxides have attracted widespread attention due to their simple synthesis methods, high specific capacity, tunable composition, and high voltage platform; however, their poor cycle stability and air stability limit their large-scale application. Prussian blue compounds have gained attention due to their low raw material cost, simple synthesis methods, and long cycle life; however, their synthesis often leads to the formation of water of crystallization, affecting battery performance. If the water of crystallization dissolves in the electrolyte, it will also threaten battery safety. Polyanionic compounds suffer from poor conductivity, and their specific capacity is low due to the large molecular weight of phosphate. Although organic materials are inexpensive and environmentally friendly, their low conductivity and low theoretical capacity also restrict their development, and current research on them is limited.

[0004] Layered transition metal oxides are classified into two types based on the coordination environment of sodium ions: O-type and P-type. When the coordination environment of sodium ions is octahedral, it is called O-type; when the coordination environment is triangular prism, it is called P-type. Based on the number of transition metal layers, they are further classified into four types: P2, P3, O2, and O3. Currently, P2 and O3 types are more widely studied, while P3 and O4 are less studied. O3 is sodium-rich, while P2 is sodium-deficient. O3 has a high theoretical capacity due to its high sodium content, but during sodium ion desorption, transition metal layer slippage easily occurs, leading to a series of irreversible phase transitions. Furthermore, O3 materials are very unstable in air, easily forming NaOH, NaCO3, etc. P2-type layered oxides are divided into manganese-based, iron-based, cobalt-based, and vanadium-based types, with manganese-based layered transition metal oxides attracting widespread attention due to their high theoretical capacity, high operating voltage, and simple synthesis methods. However, several problems exist, one being the irreversible P2-O2 phase transition during charge and discharge, causing a rapid decline in cycle performance and rate capability. Secondly, the presence of Na-Na and Na-Me electrostatic interactions between the layers leads to ordered rearrangement of sodium vacancies during sodium ion insertion / extraction, reducing the sodium ion diffusion rate. Thirdly, side reactions between the cathode material and the electrolyte cause transition metal dissolution and lattice crack formation, resulting in battery performance degradation. Fourthly, it has poor air stability. Currently, P2-Na… 0.67 Ni 0.33 Mn 0.67 O2 has attracted widespread attention due to its high operating voltage (3.8V) and high theoretical capacity. However, it still undergoes a P2-O2 phase transition during charge and discharge, causing a rapid decline in cycle performance and rate capability. Currently, the mainstream process is co-precipitation assisted by high-temperature solid-state reaction. However, the precursor particles prepared by co-precipitation are relatively large, and the distribution of elements is uneven, which affects the electrochemical performance of the material. Summary of the Invention

[0005] To address the shortcomings and deficiencies of the existing technology, the present invention aims to provide a method for preparing a dual-site co-doped sodium-ion battery cathode material; this method achieves improved P2-Na by co-doping at alkali metal sites and transition metal sites. 0.67 Ni 0.33 Mn 0.67 Cycle stability and air stability of O2 sodium-ion battery cathode materials.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a dual-site co-doped sodium-ion battery cathode material, comprising the following steps:

[0008] (1) Weigh the corresponding metal salts according to the molar ratio of each metal element in the chemical formula of the target product. Add the metal salts to a container filled with an ethanol solution and stir to dissolve them to obtain a metal salt solution. Then, take another container, add the ethanol solution and then add oxalic acid, and stir to dissolve it to obtain an oxalic acid solution. The chemical formula of the target product is Na 0.67 M x Ni 0.33-x- y N y Mn 0.67 O2, where 0 < x < 0.1, 0 < y < 0.2, M is K, Ca or Al, and N is Cu;

[0009] (2) Under ultrasonic conditions, slowly drip the metal salt solution into the oxalic acid solution while constantly stirring. After the metal salt solution is completely dripped, continue ultrasonic treatment. Place the ultrasonically treated suspension in an oven for drying, and grind the dried powder.

[0010] (3) Put the powder ground in step (2) into a corundum boat and then place it in a tube furnace for sintering. First, heat it to 500 °C for heat preservation. After cooling, take it out and press it into tablets. Then, put the pressed tablets back into the tube furnace, heat it to 900 °C for heat preservation. After cooling, take it out and grind it to obtain the target product, which is the cathode material for a dual-site co-doped sodium-ion battery.

[0011] The metal salts described in step (1) are acetates or nitrates; the molar ratio of oxalic acid to metal ions in all metal salts is 3 - 4:1.

[0012] The temperature of the oven described in step (2) is 100 °C, and the time for continued ultrasonic treatment is 1 h.

[0013] The heating rate to 500 °C in step (3) is 5 °C / min; the heat preservation time at 500 °C is 4 h; the pressure for pressing the tablets is 300 Mpa; the heating rate to 900 °C is 5 °C / min; the heat preservation time at 900 °C is 12 h.

[0014] The obtained cathode material for a dual-site co-doped sodium-ion battery has the following chemical formula: Na 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2, Na 0.67 Al 0.03 Ni 0.2 Cu 0.1 Mn 0.67 O2, Na 0.67 Al 0.05 Ni 0.18 Cu0.1 Mn 0.67 O2, Na 0.67 K 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2, Na 0.67 Ca 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2.

[0015] The present invention has the following advantages and effects compared with the prior art:

[0016] (1) The dual-site cation co-doping method proposed in this invention uses an ultrasonic-assisted co-precipitation method to uniformly distribute each element in the precursor, and then uses a high-temperature solid-state method to dope M (K, Ca, Al) into the alkali metal sites as O. 2- —M—O 2- The "pillars" enhance the electrostatic bonding force between adjacent transition metal layers, preventing cracking along the ab plane, suppressing the formation of the O2 phase during deep Na removal, and improving the material's cycle stability. Meanwhile, N doping into the transition metal sites enhances the stability of the transition metal, expands sodium ion channels, increases the sodium ion diffusion rate, and simultaneously improves air stability.

[0017] (2) The method for preparing P2-type layered manganese oxide sodium-ion battery cathode material proposed in this invention is different from the previous co-precipitation method. Based on the original co-precipitation, this invention controls the size and distribution of particles by using ultrasonic and slow drop-addition processes, so that the doped phases of the synthesized precursor are more uniformly distributed and the particle size is smaller. Attached Figure Description

[0018] Figure 1 Na in Example 1 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 XRD pattern of O2.

[0019] Figure 2 Na in Example 1 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 SEM image of O2.

[0020] Figure 3 Na in Example 1 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn0.67 EDS plot of O2.

[0021] Figure 4 Na in Example 1 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 Cycle life curve of O2 in the voltage range of 1.5-4.3V and at a rate of 0.5C.

[0022] Figure 5 Na in Example 1 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 Cycle life curve of O2 in the voltage range of 1.5-4.3V at a rate of 2C.

[0023] Figure 6 Na in Example 1 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 Ratio graph of O2 in the voltage range of 1.5-4.3V. Detailed Implementation

[0024] The following specific embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention.

[0025] Example 1: Synthesis of Na 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2

[0026] According to the synthesis of 0.01 mol Na 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67The molar ratio of Na to Ni, Mn, Cu, and Al in O2 was determined by weighing sodium acetate (5% excess), nickel acetate, manganese acetate, copper acetate, and aluminum nitrate. These metal salts were placed in a beaker, and 60 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 20 minutes until completely dissolved, yielding a metal salt solution. Next, 6 g of oxalic acid was placed in a beaker, and 30 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 10 minutes until completely dissolved, yielding an oxalic acid solution. The oxalic acid solution was placed in an ultrasonic apparatus, and the metal salt solution was slowly added dropwise while continuously stirring. After complete addition, the suspension was sonicated for another 1 hour. After sonication, the solution was dried in a 100°C oven, and the dried powder was then ground.

[0027] The ground powder was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500℃ at a heating rate of 5℃ / min and held for 4 hours. Then, it was removed, pressed into a tablet at a pressure of 300 MPa, and then placed back into the tube furnace for sintering. The tablet was heated to 900℃ at a heating rate of 5℃ / min and held for 12 hours. After naturally cooling to room temperature, it was removed and ground to obtain the dual-site co-doped P2-Na. 0.67 Ni 0.33 Mn 0.67 O2 sodium-ion battery cathode material Na 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2.

[0028] Example 2: Synthesis of Na 0.67 Al 0.03 Ni 0.2 Cu 0.1 Mn 0.67 O2

[0029] According to the synthesis of 0.01 mol Na 0.67 Al 0.03 Ni 0.2 Cu 0.1 Mn 0.67The molar ratio of Na to Ni, Mn, Cu, and Al in O2 was determined by weighing sodium acetate (5% excess), nickel acetate, manganese acetate, copper acetate, and aluminum nitrate. These metal salts were placed in a beaker, and 60 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 20 minutes until completely dissolved, yielding a metal salt solution. Next, 6 g of oxalic acid was placed in a beaker, and 30 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 10 minutes until completely dissolved, yielding an oxalic acid solution. The oxalic acid solution was placed in an ultrasonic apparatus, and the metal salt solution was slowly added dropwise while continuously stirring. After complete addition, the suspension was sonicated for another 1 hour. After sonication, the solution was dried in a 100°C oven, and the dried powder was then ground.

[0030] The ground powder was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500℃ at a heating rate of 5℃ / min and held for 4 hours. Then, it was removed, pressed into a tablet at a pressure of 300 MPa, and then placed back into the tube furnace for sintering. The tablet was heated to 900℃ at a heating rate of 5℃ / min and held for 12 hours. After naturally cooling to room temperature, it was removed and ground to obtain the dual-site co-doped P2-Na. 0.67 Ni 0.33 Mn 0.67 O2 sodium-ion battery cathode material Na 0.67 Al 0.03 Ni 0.2 Cu 0.1 Mn 0.67 O2.

[0031] Example 3: Synthesis of Na 0.67 Al 0.05 Ni 0.18 Cu 0.1 Mn 0.67 O2

[0032] According to the synthesis of 0.01 mol Na 0.67 Al 0.05 Ni 0.18 Cu 0.1 Mn 0.67The molar ratio of Na to Ni, Mn, Cu, and Al in O2 was determined by weighing sodium acetate (5% excess), nickel acetate, manganese acetate, copper acetate, and aluminum nitrate. These metal salts were placed in a beaker, and 60 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 20 minutes until completely dissolved, yielding a metal salt solution. Next, 6 g of oxalic acid was placed in a beaker, and 30 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 10 minutes until completely dissolved, yielding an oxalic acid solution. The oxalic acid solution was placed in an ultrasonic apparatus, and the metal salt solution was slowly added dropwise while continuously stirring. After complete addition, the suspension was sonicated for another 1 hour. After sonication, the solution was dried in a 100°C oven, and the dried powder was then ground.

[0033] The ground powder was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500℃ at a heating rate of 5℃ / min and held for 4 hours. Then, it was removed, pressed into a tablet at a pressure of 300 MPa, and then placed back into the tube furnace for sintering. The tablet was heated to 900℃ at a heating rate of 5℃ / min and held for 12 hours. After naturally cooling to room temperature, it was removed and ground to obtain the dual-site co-doped P2-Na. 0.67 Ni 0.33 Mn 0.67 O2 sodium-ion battery cathode material Na 0.67 Al 0.05 Ni 0.18 Cu 0.1 Mn 0.67 O2.

[0034] Example 4: Synthesis of Na 0.67 K 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2

[0035] According to the synthesis of 0.01 mol Na 0.67 K 0.01 Ni 0.22 Cu 0.1 Mn 0.67Weigh out sodium acetate (5% excess), nickel acetate, manganese acetate, copper acetate, and potassium acetate in O2 according to the molar ratio of Na to Ni, Mn, Cu, and K. Place these weighed metal salt materials in a beaker, add 60 mL of anhydrous ethanol, and stir on a magnetic stirrer for 20 minutes until completely dissolved to obtain a metal salt solution. Then, add 6 g of oxalic acid to a beaker, add 30 mL of anhydrous ethanol, and stir on a magnetic stirrer for 10 minutes until completely dissolved to obtain an oxalic acid solution. Place the oxalic acid solution in an ultrasonicator, and then slowly add the metal salt solution dropwise to the oxalic acid solution while continuously stirring. After complete addition, continue ultrasonicating the suspension for 1 hour. After ultrasonication, dry the suspension in a 100°C oven and grind the dried powder.

[0036] The ground powder was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500℃ at a heating rate of 5℃ / min and held for 4 hours. Then, it was removed, pressed into a tablet at a pressure of 300 MPa, and then placed back into the tube furnace for sintering. The tablet was heated to 900℃ at a heating rate of 5℃ / min and held for 12 hours. After naturally cooling to room temperature, it was removed and ground to obtain the dual-site co-doped P2-Na. 0.67 Ni 0.33 Mn 0.67 O2 sodium-ion battery cathode material Na 0.67 K 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2.

[0037] Example 5: Synthesis of Na 0.67 Ca 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2

[0038] According to the synthesis of 0.01 mol Na 0.67 Ca 0.01 Ni 0.22 Cu 0.1 Mn 0.67The molar ratio of Na to Ni, Mn, Cu, and Ca in O2 was determined by weighing sodium acetate (5% excess), nickel acetate, manganese acetate, copper acetate, and calcium acetate. These metal salts were placed in a beaker, and 60 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 20 minutes until completely dissolved, yielding a metal salt solution. Next, 6 g of oxalic acid was placed in a beaker, and 30 mL of anhydrous ethanol was added. The mixture was stirred on a magnetic stirrer for 10 minutes until completely dissolved, yielding an oxalic acid solution. The oxalic acid solution was placed in an ultrasonic apparatus, and the metal salt solution was slowly added dropwise while continuously stirring. After complete addition, the suspension was sonicated for another 1 hour. After sonication, the solution was dried in a 100°C oven, and the dried powder was then ground.

[0039] The ground powder was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500℃ at a heating rate of 5℃ / min and held for 4 hours. Then, it was removed, pressed into a tablet at a pressure of 300 MPa, and then placed back into the tube furnace for sintering. The tablet was heated to 900℃ at a heating rate of 5℃ / min and held for 12 hours. After naturally cooling to room temperature, it was removed and ground to obtain the dual-site co-doped P2-Na. 0.67 Ni 0.33 Mn 0.67 O2 sodium-ion battery cathode material Na 0.67 Ca 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2.

[0040] The dual-site co-doped P2-Na obtained in Example 1 above 0.67 Ni 0.33 Mn 0.67 O2 sodium-ion battery cathode material, namely Na 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2 was mixed with a conductive agent (Ketjen Black) and a binder (PVDF) at a mass ratio of 8:1:1 until homogeneous. An appropriate amount of NMP was then added to form a slurry, which was evenly coated onto aluminum foil and dried in a vacuum drying oven at 100°C for 12 hours. After drying, the foil was cut into 10mm diameter circular positive electrode sheets using a cutting machine. In a glove box, the positive electrode sheets, separator, negative sodium electrode sheet, and 1.0M sodium perchlorate were assembled into a coin cell using this electrolyte.

[0041] Figure 1 The image shown is of Na obtained in Example 1. 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67The XRD pattern of O2 shows that the diffraction peaks of the synthesized sample are sharp and correspond one-to-one with the standard PDF card. There are no obvious impurity peaks and there is a slight shift, which proves that the doping was successful.

[0042] Figure 2 The image shown is of Na obtained in Example 1. 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 The SEM image of O2 shows that the synthesized sample particles are relatively uniform in size, have a layered structure, and have no obvious layered cracks.

[0043] Figure 3 The image shown is of Na obtained in Example 1. 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 The EDS plot of O2 shows that the elements are evenly distributed.

[0044] Figure 4 , 5 The image shown is of Na obtained in Example 1. 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 The cycle life graph for O2 shows that at a 0.5C rate, the initial capacity is 140 mAh g. -1 After approximately 120 cycles, the capacity still remains at 74mAh g. -1 At a 2C rate, the initial capacity is 105.4 mAh g. -1 After approximately 470 cycles, the capacity still reaches 68.74 mAh g. -1 The capacity retention rate was 65.2%.

[0045] Figure 6 The image shown is of Na obtained in Example 1. 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 The O2 rate curve shows that from 0.1C to 10C, the capacity is still approximately 72mAh g at 10C. -1 Finally, when the rate is reduced to 0.1C, the capacity is still approximately 138mAh g. -1 The capacity difference from the initial 0.1C rate is approximately 20 mAh g. -1 It has good rate capability.

[0046] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a dual-site co-doped sodium-ion battery cathode material, characterized in that... Follow these steps: (1) Weigh the corresponding metal salts according to the molar ratio of each metal element in the chemical formula of the target product, add the metal salts to a container containing ethanol solution and stir to dissolve, to obtain a metal salt solution; then take another container, add ethanol solution and then add oxalic acid and stir to dissolve, to obtain an oxalic acid solution; the chemical formula of the target product is Na 0.67 Al 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2, Na 0.67 Al 0.03 Ni 0.2 Cu 0.1 Mn 0.67 O2, Na 0.67 Al 0.05 Ni 0.18 Cu 0.1 Mn 0.67 O2, Na 0.67 K 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2 or Na 0.67 Ca 0.01 Ni 0.22 Cu 0.1 Mn 0.67 O2; (2) Under ultrasonic conditions, the metal salt solution is added dropwise to the oxalic acid solution and stirred continuously. After the metal salt solution is completely added, ultrasonic treatment is continued. The ultrasonically treated suspension is placed in an oven for drying, and the dried powder is ground. (3) The powder ground in step (2) is placed in a corundum boat and then placed in a tube furnace for sintering. It is first heated to 500 ℃ and kept warm. After cooling, it is taken out and pressed into a sheet. The pressed sheet is then placed in the tube furnace and heated to 900 ℃ and kept warm. After cooling, it is taken out and ground to obtain the target product, which is the dual-site co-doped sodium-ion battery cathode material. In this dual-site co-doped sodium-ion battery cathode material, M is doped into the alkali metal site and N is doped into the transition metal site.

2. The method for preparing a dual-site co-doped sodium-ion battery cathode material according to claim 1, characterized in that: The metal salt in step (1) is an acetate or nitrate; the molar ratio of oxalic acid and metal ions in all metal salts is 3~4:

1.

3. The method for preparing a dual-site co-doped sodium-ion battery cathode material according to claim 1, characterized in that: The temperature of the oven in step (2) is 100 ℃, and the duration of the continued ultrasonic treatment is 1 h.

4. The method for preparing a dual-site co-doped sodium-ion battery cathode material according to claim 1, characterized in that: In step (3), the heating rate to 500 ℃ is 5 ℃ / min; the holding time to 500 ℃ is 4 h; the pressure of the tablet is 300 MPa; the heating rate to 900 ℃ is 5 ℃ / min; and the holding time to 900 ℃ is 12 h.

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