P′2 phase sodium-ion layered transition metal oxide cathode materials, their preparation methods, and applications.

Abstract

This invention provides a method for preparing a P'2 phase sodium-ion layered transition metal oxide cathode material, comprising the following steps: using a transition metal source and a sodium source as raw materials, ball milling and mixing them uniformly, heat-treating them in an air atmosphere, and then cooling them in a furnace to obtain the sodium-ion layered transition metal oxide cathode material; wherein, the sodium-ion layered transition metal oxide cathode material has a P'2 phase with the general chemical formula Na. x Ti y Mn 1‑y O2, x, y are molar ratios, 1.1 ≤ x < 1.7, 0.14 ≤ y < 0.22. The method of this invention, by adding titanium and controlling the content of sodium and titanium, obtains a P'2 phase sodium-ionized layered transition metal oxide cathode material without quenching. The obtained cathode material exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, and more specifically to a P'2 phase sodium-ion battery layered transition metal oxide cathode material, its preparation method, and its application. Background Technology

[0002] Layered transition metal oxide Na x MO2 (where M is a transition metal element) mainly includes O3 and P2-type layered transition metal oxides, in the P phase Na x The MO2 system includes two types: P2 phase and P'2 phase. Compared with the P2 phase, the P'2 phase has no manganese vacancies in its structure, and its overall structure is more highly ordered, resulting in better electrochemical performance.

[0003] P2- and P'2 phase Na x The main difference in MO2 lies in the synthesis conditions, with heating being one factor. Generally, the P'2 phase and Na... x MO2 is produced by quenching at temperatures exceeding 1000°C, resulting in a P'2 phase structure free of manganese vacancies, while the P2 phase contains Na. x The synthesis of MO2 requires heating to 900℃ followed by slow cooling. During the cooling process, oxygen from the air continuously replenishes the bulk phase of the material, causing an imbalance in the charge. To balance this charge, the P2 phase Na... x In MO2, MnIII tends to MnIV, which leads to the generation of vacancies in the Mn layer.

[0004] The quenched P'2 phase Na x MO2 avoids the above situation, so there are no manganese vacancies in the P'2 phase structure, and the overall structure is more highly ordered. However, the sintering process, which relies on quenching (>1000℃), consumes a lot of energy, affects production efficiency, and is also costly and environmentally unfriendly. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing methods for preparing P'2 phase Na. x To address the issue of high energy consumption caused by quenching at temperatures exceeding 1000℃ for MO2, a method for preparing P'2 phase sodium-ion layered transition metal oxide cathode materials is provided. This method involves adding titanium and controlling the sodium and titanium content to obtain P'2 phase Na without the need for quenching. x The cathode material obtained from MO2 exhibits excellent electrochemical performance.

[0006] According to a first aspect of the present invention, a method for preparing a P'2 phase sodium-ion layered transition metal oxide cathode material is provided, comprising the following steps:

[0007] Using transition metal source and sodium source as raw materials, the mixture is ball-milled and mixed evenly, then heat-treated in air atmosphere and cooled in furnace to obtain sodium-electric layered transition metal oxide cathode material.

[0008] The sodium-ion layered transition metal oxide cathode material has a P'2 phase and the general chemical formula Na. x Ti y Mn 1- y O2, x, y are molar ratios, 1.1≤x<1.7, 0.14≤y<0.22;

[0009] By adding titanium and controlling the content of sodium and titanium, a P'2 phase sodium-ion layered transition metal oxide cathode material can be obtained without quenching.

[0010] As an optional implementation, the masses of the transition metal source and the sodium source are prepared according to the stoichiometric ratio of the sodium-electric layered transition metal oxide cathode material.

[0011] As an optional implementation, the transition metal source contains Ti and Mn transition metal ions.

[0012] As an optional implementation, the transition metal source includes transition metal salts, transition metal oxides, or transition metal hydroxides; the transition metal salts include carbonates, acetates, nitrates, chlorides, sulfates, borates, or phosphates of transition metals.

[0013] As an optional implementation, the sodium source includes one or more of sodium carbonate, sodium nitrate, sodium sulfate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate, and sodium hydroxide.

[0014] As an optional implementation, the heat treatment conditions are: heat treatment at 1000±10℃ for 15 to 18 hours.

[0015] In a second aspect of the present invention, a P'2 phase sodium-ion layered transition metal oxide cathode material prepared by the aforementioned method is provided.

[0016] As an optional implementation, the bulk phase of the cathode material is sodium-electric layered transition metal oxide Na. x Ti y Mn 1- y O2, with no transition metal shifts or vacancies in the bulk phase; the sodium-electric layered transition metal oxide Na x Ti y Mn 1-y O2 is the P'2 phase, where x and y are the molar ratios, 1.1 ≤ x < 1.7, 0.14 ≤ y < 0.22.

[0017] According to a third aspect of the present invention, the aforementioned P'2 phase sodium-ion layered transition metal oxide cathode material is provided for use in sodium-ion batteries.

[0018] In a fourth aspect of the present invention, a sodium-ion battery is provided, which uses the aforementioned P'2 phase sodium-ion layered transition metal oxide cathode material as the cathode material.

[0019] As can be seen from the above technical solutions of the present invention, the preparation method of the P'2 phase sodium-ion layered transition metal oxide cathode material proposed in this invention, in Na x By introducing titanium into MnO2 and controlling the content of titanium and sodium, a P'2 phase sodium-electric layered transition metal oxide cathode material can be obtained without quenching through a one-step sintering method.

[0020] By setting specific high sodium conditions, sodium loss during furnace cooling and manganese vacancies caused by charge imbalance due to continuous replenishment of oxygen in the air are prevented. On this basis, by introducing a specific range of titanium elements, a fluxing effect is achieved, reducing the difficulty of the sintering process. The bulk phase can evolve into the pure P'2 phase without quenching, reducing synthesis energy consumption, improving production efficiency, reducing costs, and reducing environmental pollution.

[0021] The sodium-ion layered transition metal oxide cathode material prepared by the method of this invention suppresses the Gaines-Taylor distortion of manganese by adding a specific range of titanium elements, reducing phase transitions during cycling and making the structure of the material more stable during cycling, thus resulting in better cycling performance of the final cathode material; while controlling the range of sodium improves the initial efficiency and capacity of the material while avoiding residual alkali on the material surface; thus, the material is guaranteed to have excellent electrochemical performance. Attached Figure Description

[0022] Figure 1 These are the XRD spectra of samples prepared in Examples 1-8 and Comparative Example 1 of the present invention.

[0023] Figure 2 These are the SEM spectra of the samples prepared in Examples 1-8 and Comparative Example 1 of the present invention.

[0024] Figure 3 These are the first charge-discharge diagrams of the samples prepared in Examples 1-8 and Comparative Example 1 of the present invention at a current density of 0.01 A / g.

[0025] Figure 4 Yes, the samples prepared in Examples 1-8 and Comparative Example 1 were cycled 300 times at a current density of 0.1 A / g. Detailed Implementation

[0026] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0027] Various aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which numerous illustrative embodiments are shown. The embodiments of this disclosure are not necessarily intended to encompass all aspects of the invention. It should be understood that the various concepts and embodiments described above, as well as those described below in more detail, can be implemented in any of a number of ways.

[0028] As a manganese-based material, the P'2 phase still exhibits the inherent defects of manganese-based materials, and there is still much room for improvement in its electrochemical performance.

[0029] Cationic modification is a common method for material modification, but currently reported cationic modified materials still have certain shortcomings in terms of electrochemical performance and sintering processes. For example, copper, and ion-modified P'2 phase materials such as Na... 0.65 Mn 0.9 Cu 0.1 O2 (Yuexia Ling, 2021, 13, 58665) can increase the cycling efficiency of materials from 55% to 75% at 1C, but reduces capacity by ~60 mAh / g; another example is the P'2 phase material Na modified with nickel and iron ions as dual cations. 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 O2 (Ji Ung Choi, 2020, 10, 2001346) can retain 80% of its capacity after 200 cycles at 3C, but its capacity also decreases significantly.

[0030] Furthermore, these methods all require P'2 phase materials obtained through quenching processes at temperatures above 1000℃, resulting in significant energy consumption.

[0031] Therefore, this invention designs a method for preparing a cathode material for sodium-ion batteries, which synthesizes a P'2 phase sodium-electric layered transition metal oxide without quenching treatment, which can effectively improve energy consumption; the obtained P'2 phase sodium-electric layered transition metal oxide is modified by titanium ions, suppressing phase transition problems during cycling, and has the advantages of high initial efficiency and long cycle life.

[0032] In an exemplary embodiment of the present invention, a method for preparing a P'2 phase sodium-ion layered transition metal oxide cathode material is provided, comprising the following steps:

[0033] Using transition metal source and sodium source as raw materials, the mixture is ball-milled and mixed evenly, then heat-treated in air atmosphere and cooled in furnace to obtain sodium-electric layered transition metal oxide cathode material.

[0034] The sodium-ion layered transition metal oxide cathode material has a P'2 phase and the general chemical formula Na. x Ti y Mn 1- y O2, x, y are molar ratios, 1.1≤x<1.7, 0.14≤y<0.22;

[0035] By adding titanium and controlling the content of sodium and titanium, a P'2 phase sodium-ion layered transition metal oxide cathode material can be obtained without quenching.

[0036] As an optional example, the masses of the transition metal source and the sodium source are formulated according to the stoichiometric ratio of the sodium-electric layered transition metal oxide cathode material.

[0037] As an alternative example, in the transition metal source, the corresponding transition metal ions are Ti and Mn.

[0038] As an optional example, the transition metal source includes transition metal salts, transition metal oxides, or transition metal hydroxides; the transition metal salts include carbonates, acetates, nitrates, chlorides, sulfates, borates, or phosphates of transition metals.

[0039] As an optional example, the sodium source includes one or more of sodium carbonate, sodium nitrate, sodium sulfate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate, and sodium hydroxide.

[0040] As an optional example, the heat treatment conditions are: heat treatment at 1000±10℃ for 15~18h.

[0041] In another exemplary embodiment of the present invention, a P'2 phase sodium-ion layered transition metal oxide cathode material prepared by the aforementioned method is provided.

[0042] As an optional example, the bulk phase of the cathode material is sodium-electric layered transition metal oxide Na. x Ti y Mn 1-y O2, with no transition metal shifts or vacancies in the bulk phase; the sodium-electric layered transition metal oxide Na x Ti y Mn 1-y O2 is the P'2 phase, where x and y are the molar ratios, 1.1 ≤ x < 1.7, 0.14 ≤ y < 0.22.

[0043] In another exemplary embodiment of the present invention, an application of the aforementioned P'2 phase sodium-ion layered transition metal oxide cathode material is provided in a sodium-ion battery.

[0044] In another exemplary embodiment of the present invention, a sodium-ion battery is also provided, which uses the aforementioned P'2 phase sodium-ion layered transition metal oxide cathode material as the cathode material. This sodium-ion battery exhibits excellent rate performance and cycle stability.

[0045] To facilitate better understanding, the present invention will be further illustrated below with several specific examples, but the preparation process is not limited to these examples, and the content of the present invention is not limited to these examples.

[0046] Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0047] Example 1

[0048] Set 0.1 mol Na 1.1 Ti 0.06 Mn 0.94 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.1:0.06:0.94 (with Na source in excess of 2%, i.e., 1.1 × (1 + 0.02)) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.1 Ti 0.06 Mn 0.94 O2 is used as the positive electrode material.

[0049] Example 2

[0050] Set 0.1 mol Na 1.1 Ti 0.10 Mn 0.90 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.1:0.10:0.90 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.1 Ti 0.10 Mn 0.90 O2 is used as the positive electrode material.

[0051] Example 3

[0052] Set 0.1 mol Na 1.1 Ti 0.14 Mn 0.86O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.1:0.14:0.86 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.1 Ti 0.14 Mn 0.86 O2 is used as the positive electrode material.

[0053] Example 4

[0054] Set 0.1 mol Na 1.1 Ti 0.18 Mn 0.82 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.1:0.18:0.82 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.1 Ti 0.18 Mn 0.82 O2 is used as the positive electrode material.

[0055] Example 5

[0056] Set 0.1 mol Na 1.1 Ti 0.22 Mn 0.78 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.1:0.22:0.78 (with 2% excess Na source) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.1 Ti 0.22 Mn 0.78 As a positive electrode material.

[0057] Example 6

[0058] Set 0.1 mol Na 0.8 Ti 0.18 Mn 0.82 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) in a molar ratio of Na:Ti:Mn = 0.8:0.18:0.82 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 0.8 Ti 0.18 Mn 0.82 O2 is used as the positive electrode material.

[0059] Example 7

[0060] Set 0.1 mol Na 1.4 Ti 0.18 Mn 0.82 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.4:0.18:0.82 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.4 Ti 0.18 Mn 0.82 O2 is used as the positive electrode material.

[0061] Example 8

[0062] Set 0.1 mol Na 1.7 Ti 0.18 Mn 0.82 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 1.7:0.15:0.85 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and cooled in the furnace to obtain Na. 1.7 Ti 0.18 Mn 0.82 O2 is used as the positive electrode material.

[0063] Comparative Example 1

[0064] Set 0.1 mol Na 0.67 Ti 0.18 Mn 0.82 O2, Mn2O3, TiO2, and Na2CO3 were ball-milled (400 r / min, 6 h) at a molar ratio of Na:Ti:Mn = 0.67:0.18:0.82 (with Na source in excess of 2%) until homogeneous. The mixture was then heated at 1000℃ for 15 h and quenched to obtain Na. 0.67 Ti 0.18 Mn 0.82 O2 is used as the positive electrode material.

[0065] XRD

[0066] XRD tests were performed on the materials obtained in Examples 1-8 and Comparative Example 1, and the results are as follows: Figure 1 As shown.

[0067] As can be seen from the figure, the samples of Comparative Example 1, Examples 3, 4 and 7 are pure P'2 phase, while the phases of the other examples all contain impurities. This proves that the bulk phase of the cathode material obtained by the method of the present invention is mainly composed of P'2 phase, and the sodium content x needs to be controlled within the range of 1.1≤x<1.7 and the titanium content y within the range of 0.14≤y<0.22 in order to synthesize a pure phase.

[0068] SEM

[0069] SEM tests were performed on the materials obtained in Examples 1-8 and Comparative Example 1, and the results are as follows: Figure 2 As shown.

[0070] As can be seen from the SEM images, the samples in the comparative and example samples all exhibit irregular plate-like morphologies. Furthermore, with increasing titanium content, the plate-like morphology becomes more pronounced and the size more uniform; moreover, the plate size also increases with increasing titanium content. Simultaneously, with increasing sodium content, more small particles appear on the sample surface, indicating the formation of residual sodium carbonate. Therefore, a certain amount of sodium and titanium content is required to synthesize a pure P'2 phase and ensure the final electrochemical performance.

[0071] As can be seen from the above, the present invention successfully synthesized P'2 phase sodium-electric layered transition metal oxides without quenching, and introduced titanium elements into the transition metal layer to further modify its properties.

[0072] Electrode preparation and electrochemical performance testing

[0073] The prepared cathode material was uniformly mixed with superconducting carbon black (Super P) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP), and coated onto the surface of aluminum foil. Then, it was dried in a vacuum oven at 80°C for 10 hours to obtain a P'2 phase layered transition metal oxide electrode.

[0074] A P'2 phase layered transition metal oxide electrode was used as the positive electrode, a sodium metal sheet as the negative electrode, and 1.0 mol / L NaPF6 / propylene carbonate as the electrolyte. The two electrodes were assembled into a half cell in an argon-atmosphere glove box. The electrochemical performance of the layered transition metal oxide electrode material was tested, including specific capacity, rate performance, cycle stability, and initial coulombic efficiency. The test voltage range was 2–4.3 V.

[0075] The test results are shown in Table 1 and Figure 3-4 As shown.

[0076] Table 1

[0077]

[0078] Combination Figure 3-4 As shown in Table 1, the first efficiency, capacity, and cycle life of the material obtained without quenching are closely related to the sodium and titanium content, as well as the purity of the phase. The overall performance of the pure phase material is better than that of the multiphase material (Examples 3, 4, and 7 compared with Examples 1-2, 5-6, and 8). Furthermore, the cycle stability of the material is better with increasing titanium content, and the first efficiency is higher with increasing sodium content.

[0079] Compared to materials obtained through quenching treatment, the first-efficiency, capacity, and cycling performance of pure P'2 synthesized without quenching were significantly improved (Comparative Example 1 and Example 7), with a first-efficiency improvement of ~10% and a specific capacity as high as 213.2 mAh / g (e.g., Figure 3 As shown), after 300 cycles, there was still an 81.3% cycle retention rate (as shown). Figure 4 (As shown).

[0080] The test results from the comparative examples and embodiments show that the introduction of an appropriate amount of titanium acts as a flux, allowing the material to develop into a pure P'2 phase without quenching. It can also inhibit the migration of transition metals, greatly improving the structural stability of the material and giving it better cycle performance. If the titanium content is too low, a pure P'2 phase cannot be obtained. If the titanium content is too high, too much titanium cannot enter the transition metal layer, easily generating titanium oxide impurities, and the morphology will not reach the ideal state, thus affecting the electrochemical performance of the material.

[0081] If the sodium content is too low, a pure P'2 phase cannot be obtained; if the sodium content is increased, the material's initial efficiency will be higher, and the material's capacity can also be improved; if the sodium content is too high, impurity phases will appear, and residual alkali will appear on the material surface, which will worsen the material's electrochemical performance.

[0082] Therefore, when the amount of titanium added is 0.18 and the amount of sodium added is 1.4, the phase is pure P'2 phase, and the electrochemical performance is the best at this time. When the amount of titanium added and the amount of sodium added continue to decrease or increase, impurity phases are easily formed, and residual alkali appears on the surface of the material, which makes the electrochemical performance of the material worse.

[0083] As can be seen from the above, the method of the present invention can synthesize sodium-electric layered transition metal oxides with P'2 phase without quenching treatment, effectively improving energy consumption, suppressing phase transitions during cycling and other problems, and enabling the battery to exhibit better first-time efficiency, capacity and cycle life.

[0084] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A method for preparing a P'2 phase sodium-ion layered transition metal oxide cathode material, characterized in that, Includes the following steps: Using transition metal source and sodium source as raw materials, the mixture is ball-milled and mixed evenly, then heat-treated in air atmosphere and cooled in furnace to obtain sodium-electric layered transition metal oxide cathode material. Among them, the transition metals in the transition metal source are Ti and Mn; The mass of the transition metal source and the sodium source is prepared according to the stoichiometric ratio of the sodium-electric layered transition metal oxide cathode material. The heat treatment conditions are: heat treatment at 1000±10°C for 15~18h; The sodium-ion layered transition metal oxide cathode material has a P'2 phase and the general chemical formula Na. x Ti y Mn 1-y O2, x, y are molar ratios, 1.1≤x<1.7, 0.14≤y<0.22; the bulk phase of the sodium-electric layered transition metal oxide cathode material has no transition metal shifts or vacancies; By adding titanium and controlling the content of sodium and titanium, a P'2 phase sodium-ion layered transition metal oxide cathode material was obtained.

2. The preparation method according to claim 1, characterized in that, The transition metal source includes transition metal salts, transition metal oxides, or transition metal hydroxides; the transition metal salts include carbonates, acetates, nitrates, chlorides, sulfates, borates, or phosphates of transition metals.

3. The preparation method according to claim 1, characterized in that, The sodium source includes one or more of sodium carbonate, sodium nitrate, sodium sulfate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate, and sodium hydroxide.

4. A P'2 phase sodium-ion layered transition metal oxide cathode material prepared by the preparation method according to any one of claims 1-3, wherein the bulk phase of the cathode material is sodium-ion layered transition metal oxide Na. x Ti y Mn 1-y O2, with no transition metal shifts or vacancies in the bulk phase; the sodium-electric layered transition metal oxide Na x Ti y Mn 1-y O2 is the P'2 phase, in which, x and y are the molar ratios, where 1.1 ≤ x < 1.7 and 0.14 ≤ y < 0.

22.

5. The application of the P'2 phase sodium-ion layered transition metal oxide cathode material as described in claim 4 in sodium-ion batteries.

6. A sodium-ion battery, characterized in that, The P'2 phase sodium-ion layered transition metal oxide cathode material described in claim 4 is used as the cathode material.

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