High-capacity and high-stability manganese-based sodium-ion battery positive electrode material based on bonding ionic design and preparation method of high-capacity and high-stability manganese-based sodium-ion battery positive electrode material

Abstract

The invention discloses a high-capacity and high-stability manganese-based sodium-ion battery positive electrode material based on bonding ionic design and a preparation method, and belongs to the field of sodium-ion batteries. The general formula of the positive electrode material is P2-Na < 0.83 > Li < 0.25 > Mn < 0.7 > M < 0.05 > O < 2 >, wherein M is a metal cation. The positive electrode material is prepared by the following steps: putting a Na source, a Li source, a Mn source and an M source into a ball mill for wet ball milling through a high-temperature solid-phase one-step method, so as to obtain a positive electrode material precursor; and placing the precursor in a crucible for high-temperature calcination to obtain the required manganese-based sodium-ion battery positive electrode material. A ball milling method and a high-temperature solid-phase method are combined, and simple and efficient preparation of a target product is achieved; the required raw materials are wide in source and low in cost, the preparation process is simple and efficient, the repeatability is good, and the method is suitable for large-scale production. The obtained material has the characteristics of low cost, high specific capacity and excellent cycle performance. And the specific discharge capacity in a wide voltage range of 1.5-4.5 V can reach 180-230 mAh / g.

Description

High-capacity and high-stability manganese-based sodium-ion battery cathode material designed based on bonding ionicity and preparation method thereof Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and relates to a high-capacity and high-stability sodium-ion battery cathode material and a preparation method thereof. Background Art

[0002] With the increasing demand for the storage and utilization of renewable energy, people have been committed to developing energy storage technologies and systems that are both sustainable and efficient. Lithium-ion batteries are quite marketable due to their advantages such as high energy density, high energy conversion efficiency, long life, and environmental friendliness. However, the shortage and uneven distribution of lithium resources have greatly increased the battery cost and are not suitable for large-scale energy storage applications. Sodium resources are abundant and widely distributed, and at the same time have similar physical and chemical properties and working principles to lithium ions. Therefore, sodium-ion batteries are expected to be a beneficial alternative for large-scale energy storage. Sodium-ion batteries mainly consist of a cathode, an anode, a separator, an electrolyte, and a current collector, etc., and the cathode material is a key component affecting the electrochemical performance of sodium-ion batteries. Common cathode materials are mainly divided into three categories: layered transition metal oxides, polyanion types, and Prussian blue types. Among them, layered oxides have the characteristics of high reversible specific capacity, adjustable working voltage, and rich synthetic element selection compared with other materials, and are an important route to obtain high-performance sodium-ion batteries.

[0003] Sodium-ion battery layered oxide cathode materials can be divided into P2 type and O3 type according to the coordination environment of sodium ions and the stacking order of oxygen layers. Among them, P2-type oxides have a trigonal prism-shaped sodium ion occupancy compared with O3-type oxides, which reduces the migration barrier of sodium ions and is more conducive to improving the sodium ion diffusion kinetics of the cathode material. At the same time, the transition metal Mn element has high abundance, low price, and easy synthesis in nature. Therefore, P2-type Mn-based layered oxide Na 1-y Mn y M 1-y O2 (0.6 < x < 1.0, 0 < y < 1, M is a metal cation) has become the main research object of current researchers. However, there are also certain problems in this system of materials, such as the distortion of the MnO6 octahedron caused by the Jahn-Teller effect, the structural damage caused by the loss of lattice oxygen, and the phase change caused by the oxygen layer slip after deep sodiation, which will all lead to the decline of the electrochemical performance of the cathode material. Summary of the Invention

[0004] The purpose of this invention is to address three major problems existing in current manganese-based sodium-ion battery cathode materials: unclear structure-property relationships in high-voltage manganese-based materials, a lack of systematic summarization of elemental doping design, and scattered and theoretically repetitive existing research results. To address these problems, this invention innovatively provides a high-capacity, high-stability manganese-based sodium-ion battery cathode material and its preparation method based on bonded ionicity design. This method establishes a correlation analysis between the bonded ionicity of doping elements and their performance improvement, summarizes the screening criteria for semi-ionic elements, and ultimately obtains a high-voltage, high-capacity, and high-stability cathode material with excellent performance.

[0005] Currently, solutions to these problems mainly include bulk elemental doping and surface protective layer coating. Surface protective layer coating can effectively reduce side reactions on the cathode surface and decrease lattice oxygen loss, but the electrochemically inert protective layer affects the sodium ion insertion / extraction behavior, leading to a decrease in material capacity. Bulk elemental doping can effectively stabilize the crystal structure of the cathode material and achieve reversible charge compensation behavior by modulating the electronic band structure, thereby enabling the material to exhibit excellent overall performance. Based on this, this invention employs bulk elemental doping to improve the electrochemical performance of the target material.

[0006] This invention is based on the electronegativity theory and formulas of elements proposed by Pauling:

[0007] Ionic bond binding (%) = [1-e (-1 / 4)(XA-XB)2 (100%)

[0008] XA and XB represent the electronegativity values ​​of different elements. Here, we compare the ionic bonding between the M metal cation and the O element to determine the bonding properties of the cathode material. This helps in the targeted screening of elements with different ionic properties during experiments, thereby achieving controllable improvement in the performance of the cathode material. The carefully designed cathode material features low cost, high specific capacity (≥180 mAh / g), and long cycle stability (capacity >80% after 200 cycles). Its preparation method uses a high-temperature solid-state method, which is inexpensive, uses readily available raw materials, and has a stable process, making it suitable for large-scale production.

[0009] To achieve the above objectives, the present invention provides the following technical solution;

[0010] A high-capacity, high-stability manganese-based sodium-ion battery cathode material based on bonded ionic design, wherein the general chemical formula of the cathode material is P2-Na. 0.83 Li 0.25 Mn 0.7 M 0.05O2, where M represents various metal cations such as Ti, Mn, Fe, Co, Ni, Zn, Zr, Sn, and Sb. A series of M-doped cathode materials were synthesized using a high-temperature solid-state method, enriching the data on cathode materials with different doping characteristics. Analysis was combined with the relationship between bonding ionicity and electrochemical parameters such as capacity and cycle retention. Based on this, high-capacity and high-stability cathode materials were successfully prepared.

[0011] This invention also provides a method for preparing the above-mentioned high-capacity, high-stability manganese-based sodium-ion battery cathode material, which is prepared by a high-temperature solid-state method and specifically includes the following steps:

[0012] (1) Based on the electronegativity theory of elements and the formula for calculating the bonding ionicity proposed by Pauling above, calculate the ionicity of different doped cathode materials; then weigh the Na source, Li source, Mn source and M source according to the molar ratio of the chemical formula in the cathode material;

[0013] (2) Place the Na source, Li source, Mn source and M source weighed in step (1) into a ball mill, add an appropriate amount of organic solvent (such as ethanol, isopropanol, etc.) as solvent. The selected solvent should be able to fully dissolve the mixed powder and not react with it chemically. Then perform high-speed wet ball milling to obtain a uniformly mixed cathode material precursor.

[0014] (3) Place the cathode material precursor obtained in step (2) into a crucible and compact it. Then transfer the crucible to a muffle furnace and calcine it at high temperature in an air atmosphere. Adjust the appropriate heating rate, calcination temperature and calcination time according to the different instruments to synthesize the required high-capacity sodium-ion battery cathode material in one step.

[0015] Further, in step (1), the Na source is one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium nitrate or sodium citrate; the Li source is one or more of lithium carbonate, lithium hydroxide, lithium acetate or sodium nitrate; the Mn source is one or more of manganese carbonate, manganese acetate, manganese dioxide, manganese trioxide or manganese oxide; and the M source is one or more of the sulfate, nitrate, acetate or oxide of M.

[0016] Furthermore, in step (1), the Na source is in excess of sodium element by 2% to 8%, and the excess Na source is mainly used to compensate for the volatilization loss of the Na source during the high-temperature calcination process.

[0017] Furthermore, in step (2), the stirring rate of the ball mill is in the range of 300~500 rpm, and the time is 6~30h.

[0018] Furthermore, in step (3), the experimental conditions for high-temperature calcination are: calcination temperature of 800~1000 ℃, heating rate of 2~10 ℃ / min, and calcination time of 10~24 h.

[0019] Advantages and beneficial effects of the present invention:

[0020] The P2-type layered manganese-based sodium-ion battery cathode material provided by this invention features low cost, high specific capacity, and excellent cycle performance. The discharge specific capacity can reach 180-230 mAh / g over a wide voltage range of 1.5-4.5 V. Capacity fluctuations originate from changes in bonding ionicity introduced by different doping elements, thus significantly affecting the cathode material's performance.

[0021] This invention combines ball milling and high-temperature solid-state methods to achieve simple and efficient preparation of the target product. At the same time, based on the electronegativity theory and formula proposed by Pauling, it effectively summarizes the optimal bonding ionicity range in the cathode material system and guides the selection of the optimal doping element, providing a strong theoretical support for the preparation of high-capacity and high-stability cathode materials.

[0022] The raw materials used in this invention are widely available and inexpensive, and the preparation process is simple, efficient, and highly reproducible, making it suitable for large-scale production. This invention not only provides theoretical guidance and a technical pathway for P2-type layered oxide sodium-ion battery cathode materials, but also offers crucial support for the practical application of sodium-ion batteries in large-scale energy storage. Attached Figure Description

[0023] Figure 1 shows the X-ray diffraction (XRD) patterns of the manganese-based sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 of the present invention;

[0024] Figure 2 is a comparison of the cycle performance of the manganese-based sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0025] Figure 3 shows the relationship between capacity and retention rate of the manganese-based sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 of this invention, with labels indicating their bonding ionicity. Simultaneously, predictions were made for high-capacity, high-stability semi-ionic doped cathodes.

[0026] Figure 4 is a correlation diagram of the capacity / retention rate and bonding ionicity of the manganese-based sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 of the present invention.

[0027] Figure 5 is a comparison of the charge-discharge curves of the manganese-based sodium-ion battery cathode materials prepared in Example 2 and Comparative Example 1 of the present invention.

[0028] Figure 6 is a comparison of the cycle performance of the manganese-based sodium-ion battery cathode materials prepared in Example 2 and Comparative Example 1 of the present invention. Detailed Implementation

[0029] The following specific embodiments, in conjunction with the accompanying drawings, further illustrate the present invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from its spirit and essence are within the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0030] Example 1

[0031] According to the present invention, a high-capacity, high-stability cathode material was synthesized based on the calculation of bonded ionic properties. Eight cathode materials, including P2-Na, were prepared by combining ball milling and high-temperature solid-state methods. 0.83 Li 0.25 Mn 0.7 Ti 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Fe 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Co 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Ni 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Cu 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Zn 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Zr 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Sb 0.05 The specific synthesis steps for O2 are as follows:

[0032] (1) According to the molar ratio of the positive electrode material chemical formula: 0.83:0.25:0.7:0.05, the corresponding masses of sodium carbonate, lithium carbonate, manganese dioxide and eight different metal oxides (iron oxide / cobalt oxide / nickel oxide / titanium oxide / zinc oxide / zirconium oxide / antimony pentoxide) were weighed. Sodium carbonate was weighed in excess by 5% based on sodium element to compensate for the loss caused by the volatilization of Na source at high temperature during the subsequent preparation process.

[0033] (2) Transfer each raw material to a ball mill jar (place each of the eight different metal oxides into three ball mill jars respectively), set the ball mill speed to 400 rpm, and the ball milling time to 15 h to obtain three cathode material precursors.

[0034] (3) The eight precursors were compacted in crucibles; then heated to 900 °C at a heating rate of 5 °C / min and calcined in air for 18 h, and then cooled to room temperature naturally to obtain eight high-capacity sodium-ion battery cathode materials P2-Na. 0.83 Li 0.25 Mn 0.7 Ti 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Fe 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Co 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Ni 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Cu 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Zn 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Zr 0.05 O2, P2-Na 0.83 Li 0.25 Mn 0.7 Sb 0.05 O2.

[0035] Example 2

[0036] According to the present invention, a method for preparing high-capacity, high-stability cathode materials based on bonded ionicity calculations is used. This method combines ball milling and high-temperature solid-state methods to prepare semi-ionic, semi-covalently bonded cathode materials. Simultaneously, the composition is optimized by screening different Zn doping contents, ultimately yielding a high-performance cathode material: P2-Na. 0.83 Li 0.2 Mn 0.7 Zn 0.1 The specific synthesis steps for O2 are as follows:

[0037] (1) Weigh out the corresponding masses of sodium carbonate, lithium carbonate, manganese dioxide and zinc oxide according to the molar ratio of 0.83:0.2:0.7:0.1. Among them, sodium carbonate is weighed in excess by 3% as sodium element to make up for the loss caused by sodium volatilization at high temperature during the subsequent preparation process.

[0038] (2) Transfer each raw material to a ball mill jar, set the ball mill speed to 500 rpm, and the ball milling time to 24 h to obtain the cathode material precursor.

[0039] (3) The precursor was compacted in a crucible; then heated to 700 °C at a heating rate of 3 °C / min and calcined in air for 12 h, followed by natural cooling to room temperature to obtain the low-cost, high-capacity sodium-ion battery cathode material P2-Na. 0.83 Li 0.2 Mn 0.7 Zn 0.1 O2.

[0040] Comparative Example 1

[0041] According to the preparation method of the high-capacity, high-stability sodium-ion battery cathode material of the present invention, P2-Na is prepared by combining ball milling and high-temperature solid-state method. 0.83 Li 0.25 Mn 0.75 The specific synthesis steps for O2 (without doped metal cations) are as follows:

[0042] (1) Weigh out the corresponding masses of sodium carbonate, lithium carbonate and manganese dioxide according to the molar ratio of 0.83:0.25:0.75. Among them, sodium carbonate is weighed in excess by 5% as sodium element to make up for the loss caused by sodium volatilization at high temperature during the subsequent preparation process.

[0043] (2) Transfer each raw material to a ball mill jar, set the ball mill speed to 400 rpm, and the ball milling time to 24 h to obtain the cathode material precursor.

[0044] (3) The precursor was compacted in a crucible; then heated to 800 °C at a heating rate of 5 °C / min and calcined in air for 24 h, and then cooled naturally to room temperature to obtain the sodium-ion battery cathode material P2-Na for effect comparison. 0.83 Li 0.25 Mn 0.75 O2.

[0045] Performance testing

[0046] The active material (the positive electrode powder obtained from the above synthesis), the conductive agent (Super P), and the binder polyvinylidene fluoride (PVDF) were weighed out in a mass ratio of 7:2:1. After the powder was thoroughly ground and homogenized, an appropriate amount of positive electrode homogenizing solvent (NMP) was added dropwise and the mixture was ground again to obtain a positive electrode slurry with good flowability. Subsequently, the slurry was coated onto an Al foil current collector and then transferred to a vacuum drying oven to dry at 120 °C for 12 h. Finally, it was cut into circular electrode sheets with a diameter of 10 mm using a manual cutting machine and properly stored for later use.

[0047] The coin cell assembly uses a CR2032 coin cell casing, assembled in the following order: positive electrode casing, positive electrode plate, separator, negative electrode plate (sodium plate), stainless steel gasket, stainless steel spring plate, and negative electrode casing. The casing is then sealed using a sealing machine under 50 MPa pressure. Approximately 160 microliters of electrolyte are used for each coin cell, dripped onto the negative electrode side of the separator to ensure thorough wetting. The entire coin cell assembly process is performed in a glove box under an argon atmosphere. After assembly, the coin cells are left overnight to allow the system to stabilize.

[0048] In this invention, all electrochemical performance tests were conducted at room temperature, and the battery test voltage range was 1.5–4.5 V. Charge-discharge test results show that the material exhibits directionally controllable high capacity and high stability (see Table 1).

[0049] Table 1

[0050]

[0051] X-ray diffraction (XRD) tests were performed on the layered oxide cathode materials prepared in Example 1 and Comparative Example 1, and the results are shown in Figure 1. Comparative Example 1 was used as the initial sample, and P2-Na, a widely studied material, was selected. 0.83 Li 0.25 Mn 0.75Using O2-type layered oxide as the substrate material, a novel cathode material with optimized structure was obtained in Example 1 through different ionic doping processes. XRD analysis was used to quickly and effectively analyze the phase composition purity and crystallographic characteristics of the material. The results showed that all diffraction peaks of the material belonged to the P63 / mmc space group. In particular, a significant superlattice structure diffraction peak was observed near 22°, indicating the ordered arrangement of Li / TM ions in the transition metal layer. No other impurity phases were observed, indicating that the novel cathode material prepared by this method possesses a pure P2-phase layered structure and excellent crystallinity.

[0052] Figure 2 shows the results of Example 1 and Comparative Example 1 at 200 mAg. -1 The performance comparison after 200 cycles at different current densities includes information on capacity, rate capability, and stability. Figure 3 shows the correlation between the bonding ionicity of different doped materials and cathode performance. It was found that, using Pauling's calculation formula, dopants can be divided into two categories: low bonding ionicity (marked in red) and high bonding ionicity (marked in blue). Data demonstrates that the significant difference in bonding ionicity leads to a polarization of cathode materials: when bonding ionicity < 0.5, the material exhibits high capacity (~160 mAh / g); when bonding ionicity > 0.5, the material exhibits high retention rate (~75%), providing a theoretical framework for designing high-capacity, high-stability cathodes. Based on this theory, Figure 4 shows a screening method for bonding ionicity values ​​versus performance spectra, and an optimized range of 0.5-0.55 was selected. When the bonding ionicity parameter is within this range, the material is expected to achieve synergistic optimization of high capacity and high stability. The sample obtained through component optimization exhibited the expected dual improvement, as shown in Figures 5 and 6: Figure 5 shows that the specific capacity of sample 2 increased by 25% compared to the original sample; Figure 6 shows that sample 2 maintained 80% capacity retention after 100 cycles, significantly better than the original sample. The control scheme based on the bonded ionicity established in this invention not only demonstrates clear design guidance significance in manganese-based sodium ion cathode material systems, but can also be extended to other layered materials, providing a universal solution for flexibly customizing high-performance cathode materials.

Claims

1. A high-capacity, high-stability manganese-based sodium-ion battery cathode material based on bonded ionic design, characterized in that, The general chemical formula of the cathode material is P2-Na. 0.83 Li 0.25 Mn 0.7 M 0.05 O2, where M is a metal cation.

2. The high-capacity, high-stability manganese-based sodium-ion battery cathode material according to claim 1, characterized in that, M is a metal cation of Ti, Mn, Fe, Co, Ni, Zn, Zr, Sn, or Sb.

3. The method for preparing the high-capacity, high-stability manganese-based sodium-ion battery cathode material according to claim 1 or 2, characterized in that, The preparation method is a high-temperature solid-state method, which includes the following steps: (1) Based on the electronegativity theory and formula of elements proposed by Pauling: Ionic bond (%) = [1-e (-1 / 4)(XA-XB)2 (100%) Where XA and XB represent the electronegativity values ​​of different elements. By comparing the ionic bond between the M metal cation and the O element, the bonding properties of the cathode material are determined to assist in the directional screening of elements with different ionic properties in the experiment, thereby achieving controllable improvement of the cathode material performance. Then, according to the molar ratio of the chemical formula in the cathode material, Na source, Li source, Mn source and M source are weighed. (2) The Na source, Li source, Mn source and M source weighed in step (1) are placed in a ball mill, and an organic solvent is added. The selected solvent should be able to fully dissolve the mixed powder and not react with it chemically. Then, wet ball milling is performed to obtain a uniformly mixed cathode material precursor. (3) The cathode material precursor obtained in step (2) is placed in a crucible and compacted. Then, the crucible is transferred to a muffle furnace and calcined at high temperature in an air atmosphere. The heating rate, calcination temperature and calcination time are controlled to synthesize the required manganese-based sodium ion battery cathode material in one step.

4. The method for preparing the manganese-based sodium-ion battery cathode material according to claim 3, characterized in that, In step (1), the Na source is one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium nitrate or sodium citrate; the Li source is one or more of lithium carbonate, lithium hydroxide, lithium acetate or sodium nitrate; the Mn source is one or more of manganese carbonate, manganese acetate, manganese dioxide, manganese trioxide or manganese oxide; and the M source is one or more of the sulfate, nitrate, acetate or oxide of M.

5. The method for preparing the manganese-based sodium-ion battery cathode material according to claim 3, characterized in that, In step (1), the Na source is in excess of sodium element by 2% to 8%. The excess Na source is mainly used to compensate for the volatilization loss of the Na source during the high-temperature calcination process.

6. The method for preparing the manganese-based sodium-ion battery cathode material according to claim 3, characterized in that, In step (2), the stirring rate of the ball mill is 300~500 rpm and the stirring time is 6~30 h.

7. The method for preparing the manganese-based sodium-ion battery cathode material according to claim 3, characterized in that, In step (3), the conditions for high-temperature calcination are: calcination temperature of 800~1000 ℃, heating rate of 2~10 ℃ / min, and calcination time of 10~24 h.

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