Preparation method of ca-doped sodium-ion battery layered oxide positive electrode material

Abstract

This invention belongs to the field of sodium-ion battery technology and discloses a method for preparing Ca-doped layered oxide cathode material for sodium-ion batteries. This method is simple, with a straightforward process, and uses inexpensive, non-toxic, and pollution-free raw materials, offering significant cost and environmental advantages. This method utilizes Ca... 2+ Introduced into the crystal structure, it partially replaces Mn 2+ Na, a layered oxide cathode material for sodium-ion batteries, was prepared. 0.67 Co 0.5 Mn 0.5‑x Ca x O2 exhibits superior cycle stability and better rate performance compared to the undoped form. This method uses a planetary ball mill to ball-mill the sample, controlling the particle size and distribution by adjusting the ball-to-material ratio, milling time, and rotation speed, resulting in a more uniform distribution of doped phases and smaller particle size in the synthesized precursor.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and specifically relates to a Ca-doped P2-Na 0.67 Co 0.5 Mn 0.5 Preparation method of layered oxide cathode material for sodium ion batteries (O2). Background Technology

[0002] The urgency of developing clean energy technologies has spurred extensive research into high-energy, low-cost energy storage devices for large-scale grid storage. From a cost and sustainability perspective, sodium-ion batteries are more attractive than lithium-ion batteries because they are more abundant and have a greater cost advantage. The basic principles and characteristics of sodium-ion and lithium-ion batteries are similar in many ways. Therefore, we can consider the suitability of lithium-ion batteries for lithium-ion batteries... + Starting with the structure and chemistry of ion insertion, the search for viable cathode materials for sodium-ion batteries begins.

[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 (O3: ABCABC stack, P2: ABBA stack, P3: ABBCCA stack). Currently, P2 and O3 types are more widely studied, while P3 and O4 are less studied. O3 type cathode materials have sufficient Na... + The reservoir capacity and high energy density are advantageous for constructing high-energy full-cell applications. However, the application of O3-type cathode materials in high-performance sodium-ion batteries still faces some challenges. +The diffusion path requires a high activation energy. The P2-type structure has open Na+ transport channels, and the Na+ diffusion barrier is lower than that of the O3-type structure. Therefore, the P2-type structure is less prone to structural phase transitions during Na+ extraction / insertion and exhibits higher rate performance than the O3-type structure. P2-type materials typically exhibit excellent reversibility and high discharge capacity, thanks to direct sodium-ion diffusion between the two facet-shared triangular prism sites. However, the initial Na content of P2-type cathode materials is lower than that of O3-type cathode materials, so the theoretical capacity of P2-type cathode materials is lower than that of O3-type cathode materials. The coulombic efficiency anomaly observed in the first cycle of a full cell for P2-type cathode materials limits their practical application. Because P2-type Na... 0.67 Co 0.5 Mn 0.5 O2 exhibits excellent electrochemical performance and structural flexibility, with high capacity, good cycle stability, and outstanding rate capability, making it a focus of attention in the sodium-ion battery field. However, the redox voltages of cobalt and manganese are not fixed at low voltages and vary greatly with their composition. Furthermore, they still suffer from drawbacks such as poor cycle stability and rate performance. Summary of the Invention

[0005] To overcome the shortcomings and deficiencies of existing technologies, the present invention aims to provide a method for preparing Ca-doped sodium-ion battery layered oxide cathode materials, thereby improving the P2-Na content by doping the transition metal sites. 0.67 Co 0.5 Mn 0.5 Cycle stability and rate performance of layered oxide cathode materials for sodium-ion batteries.

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

[0007] A method for preparing a Ca-doped layered oxide cathode material for sodium-ion batteries includes the following steps:

[0008] (1) According to the chemical formula Na 0.67 Co 0.5 Mn 0.5-x Ca x Weigh out the corresponding sodium, cobalt, manganese and calcium sources in O2 and add them to a 100ml corundum ball mill jar. Set the bead ratio to 1:10-30, the rotation speed to 300-400r / min, the time to 8h-12h, and alternate between forward and reverse rotation for ball milling. The resulting powder is the precursor of sodium-ion battery cathode material.

[0009] (2) The precursor of sodium-ion battery cathode material was sintered in a tube furnace. First, it was heated to 500 °C at a heating rate of 5 °C / min and held for 4 h. Then, it was taken out and pressed into sheets under a pressure of 500 MPa. It was then placed back into the tube furnace for sintering. The temperature was increased to 900 °C at a heating rate of 5 °C / min and held for 12 h. After natural cooling to room temperature, it was taken out and ground to obtain Ca-doped sodium-ion battery layered oxide cathode material. The chemical formula of the obtained Ca-doped sodium-ion battery layered oxide cathode material is Na 0.67 Co 0.5 Mn 0.5-x Ca x O2, where 0 <x<0.1。

[0010] The resulting Ca-doped sodium-ion battery layered oxide cathode material has the following chemical formula:

[0011] Na 0.67 Co 0.5 Mn 0.49 Ca 0.01 O2,

[0012] Na 0.67 Co 0.5 Mn 0.47 Ca 0.03 O2,

[0013] Na 0.67 Co 0.5 Mn 0.45 Ca 0.05 O2,

[0014] Na 0.67 Co 0.5 Mn 0.43 Ca 0.07 O2.

[0015] The sodium source in step (1) is one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium nitrate, and sodium citrate; the cobalt source is one or more of cobalt acetate, cobalt oxide, and cobalt carbonate; the manganese source is one or more of manganese oxide, zinc acetate, and manganese carbonate; and the calcium source is one or more of copper oxide, lithium carbonate, zinc acetate, and calcium acetate.

[0016] The present invention has the following advantages and beneficial effects compared with the prior art:

[0017] (1) The Ca doping method of the present invention is simple to implement, has a simple process flow, and uses inexpensive, non-toxic, and non-polluting raw materials, which has great cost and environmental advantages; this method will dope Ca 2+ Introduced into the crystal structure, it partially replaces Mn 2+Na, a layered oxide cathode material for sodium-ion batteries, was prepared. 0.67 Co 0.5 Mn 0.5-x M x O2 exhibits superior cycle stability and better rate performance compared to the undoped form.

[0018] (2) The method for preparing P2 type sodium-ion battery layered oxide cathode material proposed in this invention uses a planetary ball mill to ball mill the sample. By adjusting the ball-to-material ratio, ball milling time and rotation speed, the size and distribution of particles are controlled, so that the doped phases of the synthesized precursor are more uniformly distributed and the particle size is smaller. Attached Figure Description

[0019] Figure 1 Na in Example 3 0.67 Co 0.5 Mn 0.45 Ca 0.05 XRD pattern of O2;

[0020] Figure 2 Na in Example 3 0.67 Co 0.5 Mn 0.45 Ca 0.05 SEM image of O2;

[0021] Figure 3 Na in Example 3 0.67 Co 0.5 Mn 0.45 Ca 0.05 EDS plot of O2;

[0022] Figure 4 Na in Example 3 0.67 Co 0.5 Mn 0.45 Ca 0.05 Cycle life curve of O2 in the voltage range of 1.5-4.3 V and at a rate of 2 C. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0024] Example 1: Synthesis of Na 0.67 Co 0.5 Mn 0.49 Ca 0.01 O2

[0025] According to the synthesis of 0.01 mol Na 0.67 Co 0.5 Mn 0.49 Ca 0.01The molar ratio of each element in O2 is determined by weighing sodium acetate (5% excess), cobalt acetate, manganese acetate, and calcium acetate. The weighed materials are placed in a corundum ball mill jar, with a material-to-bead ratio of 1:20, a rotation speed of 400 r / min, a time of 8 h, and alternating between forward and reverse rotation for milling. The resulting powder is the precursor of the sodium-ion battery cathode material.

[0026] The obtained sodium-ion battery cathode material precursor was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500 °C at a heating rate of 5 °C / min and held for 4 h. Then, it was removed, pressed into a sheet at a pressure of approximately 500 MPa, and then placed back into the tube furnace for sintering. The sheet was heated to 900 °C at a heating rate of 5 °C / min and held for 12 h. After natural cooling to room temperature, it was removed and ground to obtain Ca-doped P2-Na. 0.67 Co 0.5 Mn 0.5 O2 sodium-ion battery cathode material Na 0.67 Co 0.5 Mn 0.49 Ca 0.01 O2.

[0027] Example 2: Synthesis of Na 0.67 Co 0.5 Mn 0.47 Ca 0.03 O2

[0028] According to the synthesis of 0.01 mol Na 0.67 Co 0.5 Mn 0.47 Ca 0.03 The molar ratio of each element in O2 is determined by weighing sodium acetate (5% excess), cobalt acetate, manganese acetate, and calcium acetate. The weighed materials are placed in a corundum ball mill jar, with a material-to-bead ratio of 1:20, a rotation speed of 400 r / min, a time of 8 h, and alternating between forward and reverse rotation for milling. The resulting powder is the precursor of the sodium-ion battery cathode material.

[0029] The obtained sodium-ion battery cathode material precursor was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500 °C at a heating rate of 5 °C / min and held for 4 h. Then, it was removed, pressed into a sheet at a pressure of approximately 500 MPa, and then placed back into the tube furnace for sintering. The sheet was heated to 900 °C at a heating rate of 5 °C / min and held for 12 h. After natural cooling to room temperature, it was removed and ground to obtain Ca-doped P2-Na. 0.67 Co 0.5 Mn 0.5 O2 sodium-ion battery cathode material Na 0.67 Co 0.5 Mn 0.47 Ca 0.03O2.

[0030] Example 3: Synthesis of Na 0.67 Co 0.5 Mn 0.45 Ca 0.05 O2

[0031] According to the synthesis of 0.01 mol Na 0.67 Co 0.5 Mn 0.45 Ca 0.05 The molar ratio of each element in O2 is determined by weighing sodium acetate (5% excess), cobalt acetate, manganese acetate, and calcium acetate. The weighed materials are placed in a corundum ball mill jar, with a material-to-bead ratio of 1:20, a rotation speed of 400 r / min, a time of 8 h, and alternating between forward and reverse rotation for milling. The resulting powder is the precursor of the sodium-ion battery cathode material.

[0032] The obtained sodium-ion battery cathode material precursor was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500 °C at a heating rate of 5 °C / min and held for 4 h. Then, it was removed, pressed into a sheet at a pressure of approximately 500 MPa, and then placed back into the tube furnace for sintering. The sheet was heated to 900 °C at a heating rate of 5 °C / min and held for 12 h. After natural cooling to room temperature, it was removed and ground to obtain Ca-doped P2-Na. 0.67 Co 0.5 Mn 0.5 O2 sodium-ion battery cathode material Na 0.67 Co 0.5 Mn 0.45 Ca 0.05 O2.

[0033] Example 4: Synthesis of Na 0.67 Co 0.5 Mn 0.43 Ca 0.07 O2

[0034] According to the synthesis of 0.01 mol Na 0.67 Co 0.5 Mn 0.43 Ca 0.07 The molar ratio of each element in O2 is determined by weighing sodium acetate (5% excess), cobalt acetate, manganese acetate, and calcium acetate. The weighed materials are placed in a corundum ball mill jar, and the ball ratio is set to 1:20. The rotation speed is set to 400 r / min, the time is set to 8 h, and the forward and reverse rotations are alternated.

[0035] The obtained sodium-ion battery cathode material precursor was placed in a corundum boat and then sintered in a tube furnace. First, it was heated to 500 °C at a heating rate of 5 °C / min and held for 4 h. Then, it was removed, pressed into a sheet at a pressure of approximately 500 MPa, and then placed back into the tube furnace for sintering. The sheet was heated to 900 °C at a heating rate of 5 °C / min and held for 12 h. After natural cooling to room temperature, it was removed and ground to obtain Ca-doped P2-Na. 0.67 Co 0.5 Mn 0.5 O2 sodium-ion battery cathode material Na 0.67 Co 0.5 Mn 0.43 Ca 0.07 O2.

[0036] The Ca-doped P2-Na obtained in Example 3 0.67 Co 0.5 Mn 0.5 The positive electrode material of the O2 sodium-ion battery is mixed with a conductive agent (Ketjen Black) and a binder (PVDF) at a mass ratio of 7:2:1. An appropriate amount of NMP is then added to form a slurry, which is evenly coated onto aluminum foil and dried in a vacuum drying oven at 100 °C for 12 h. After drying, the slurry is cut into 10 mm diameter circular positive electrode sheets using a cutting machine. In a glove box, the positive electrode sheets, separator, negative sodium electrode sheet, and 1.0 M sodium perchlorate as the electrolyte are assembled to obtain a coin cell.

[0037] Figure 1 ShownNa 0.67 Co 0.5 Mn 0.45 Ca 0.05 The 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.

[0038] Figure 2 ShownNa 0.67 Co 0.5 Mn 0.45 Ca 0.05 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.

[0039] Figure 3 ShownNa 0.67 Co 0.5 Mn 0.45 Ca 0.05 The EDS diagram of O2 shows that the elements are evenly distributed, and Ca is doped into the material.

[0040] Figure 4 ShownNa 0.67 Co 0.5 Mn0.45 Ca 0.05 The cycle life graph for O2 shows that at a 2C rate, the initial capacity is 138.2 mAh g⁻¹. -1 After approximately 100 cycles, the capacity still reaches 88.3 mAh g. -1 The capacity retention rate was 63.9%.

[0041] 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 Ca-doped sodium-ion battery layered oxide cathode material, characterized in that, The following steps are included: (1) Sodium acetate, cobalt acetate, manganese acetate and calcium acetate are weighed according to the molar ratio of each element in the chemical formula Na 0.67 Co 0.5 Mn 0.45 Ca 0.05 O2, and are added into a 100ml corundum ball mill jar, the material bead ratio is set to 1:20, the rotation speed is set to 400r / min, the time is set to 8h, and the ball milling is carried out alternately in forward and reverse rotation, and the obtained powder is the positive electrode material precursor of the sodium ion battery. (2) The sodium-ion battery cathode material precursor was sintered in a tube furnace. It was first heated to 500 °C at a heating rate of 5 °C / min and held for 4 h. Then, it was removed and pressed into sheets under a pressure of 500 MPa, and then placed back into the tube furnace for sintering. The temperature was increased to 900 °C at a heating rate of 5 °C / min and held for 12 h. After natural cooling to room temperature, it was removed and ground to obtain the Ca-doped P2 type sodium-ion battery layered oxide cathode material. The chemical formula of the obtained Ca-doped P2 type sodium-ion battery layered oxide cathode material is Na. 0.67 Co 0.5 Mn 0.45 Ca 0.05 O2.

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