Positive electrode material and preparation method and application thereof

Abstract

The invention provides a positive electrode material as well as a preparation method and application thereof. The positive electrode material comprises a layered oxide, the layered oxide comprises an O3 phase and an O '3 phase; the molar fraction of the O3 phase is 65%-85%, and the molar fraction of the O '3 phase is 15%-35%; the chemical formula of the layered oxide is NaMnxNiyCuZO2, x is more than or equal to 0.45 and less than or equal to 0.55, y is more than or equal to 0.3 and less than or equal to 0.42, and z is more than or equal to 0.08 and less than or equal to 0.2. In the O3 / O '3 hybrid phase layered oxide positive electrode material, the phase composition, the structural stability, the capacity, the energy density and the interface compatibility of the positive electrode material are adjusted by limiting the proportion of sodium, manganese, nickel, copper and oxygen, so that the high cycle performance of the positive electrode material is improved; the hybrid phase structure in the positive electrode material can improve sodium ion diffusion and air stability and inhibit complex phase change, so that the rate capability and cycle performance of the positive electrode material are improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium batteries, and in particular to a positive electrode material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries (SIBs) are secondary batteries (rechargeable batteries) that rely primarily on the movement of sodium ions between the positive and negative electrodes. The electrode materials used in SIBs are primarily sodium salts, which are more abundant and less expensive than lithium salts. Because sodium ions are larger than lithium ions, SIBs are a cost-effective alternative when weight and energy density are less critical.

[0003] The general requirements for the positive electrode materials of sodium ion batteries include: (1) good reversibility of the insertion and extraction process and stable structure during charging and discharging; (2) small changes in the material structure during charging and discharging; (3) high chemical diffusion coefficient of sodium ions in the material, which can be quickly inserted and extracted; (4) high electronic conductivity and ionic conductivity; (5) non-toxic, abundant resources, low cost, easy to prepare and environmentally friendly; (6) the positive electrode material acts as a sodium source; (7) provides a higher electrode potential; (8) the voltage platform is continuous and stable; (9) the electrochemical equivalent of the active material is small and the amount of ions that can be reversibly inserted and extracted is large; (10) high chemical stability in the electrolyte; (11) high stability over a wide temperature range.

[0004] The structures of layered oxide cathode materials for sodium-ion batteries are classified as P-type or O-type (P3, P2, and O3 phase structures) based on the coordination environment of sodium ions and the stacking pattern of oxygen. The letters P and O represent the triangular prism and octahedral coordination environments of sodium ions, respectively. The numbers represent the number of transition metal layers per repeating unit in the crystal structure. In P2-type layered oxides, sodium ions are located in triangular prism positions, providing wider sodium ion diffusion pathways and facilitating sodium ion diffusion. However, at high voltages (above 4.2V), the P2 structure undergoes a detrimental phase transition, causing the initial structure to transform into the O2 phase, resulting in a large volume change and severely affecting cycling performance. Similarly, the P3 to O3 phase transition at high voltages also presents the problem of irreversible phase transition. O3-phase materials have a high theoretical capacity due to their high initial sodium ion content, but as sodium ions are released, they undergo a series of complex phase transitions, resulting in poor cycling stability. Furthermore, the sodium ions in O-type materials are located in octahedral positions, resulting in poor diffusion kinetics.

[0005] Considering that the cycle stability of single-phase materials still cannot meet the actual requirements, designing a multiphase structure is one of the effective strategies to improve battery performance. Its purpose is to take advantage of the strengths and weaknesses of different structures to achieve synergistic effects. Metal cation doping is a typical method for preparing multiphase structures. For example, by doping Ti4+ 、Li + 、Cu 2+ 、Zn 2+ Elements such as P3 / O3, P2 / O3, and P2 / P3 can be used to prepare composite materials. Compared with single-phase materials, the electrochemical performance of these composite positive electrode materials is generally improved. Chinese patent document CN201710003808.9 discloses a modified O3-type sodium ion battery layered positive electrode material and its preparation method. Na2CO3, Mn2O3, and NiO2 are placed in a high-speed mixer and evenly mixed. Then, they are pressed into sheets at a pressure of 20Mpa and sintered at 1000℃ for 15h to obtain NaNi 0.5 Mn 0.5 O2 positive electrode material, the size of the material powder particles is 5 to 10 μm, the obtained NaNi 0.5 Mn 0.5 O2 cathode material at 0.1C (24mAg -1 ) after 100 cycles at a specific rate, the capacity retention rate is only 44%, which is difficult to meet the requirements of large-scale electrochemical energy storage systems. Summary of the Invention

[0006] This application is made in view of the fact that the cyclic stability of single-phase materials in the existing technology cannot meet actual requirements. Its purpose is to provide a positive electrode material and its preparation method and application, and to achieve synergistic effect by taking advantage of the characteristics of different phase structures in multi-phase materials to obtain O3 / O'3 hybrid phase layered oxide positive electrode materials with good stability, high specific capacity, high first coulombic efficiency and excellent cycle performance, thereby improving battery performance through the multi-phase structure of the positive electrode material.

[0007] Specifically as follows, a first aspect of the present application provides a positive electrode material, including a layered oxide;

[0008] The layered oxide includes an O3 phase and an O'3 phase;

[0009] The molar fraction of the O3 phase is 65% to 85%, and the molar fraction of the O'3 phase is 15% to 35%.

[0010] Furthermore, the chemical formula of the layered oxide is NaMnxNiyCu Z O2, where 0.45≤x≤0.55, 0.3≤y≤0.42, 0.08≤z≤0.2, X+Y+Z=1.

[0011] The second aspect of the present application provides a method for preparing the positive electrode material, comprising the following steps:

[0012] S1: Sodium source, manganese source, nickel source and copper source are mixed by ball milling and then pressed to prepare a precursor;

[0013] S2: sintering the precursor once and twice;

[0014] During the secondary sintering process, a sodium source needs to be added for further ball milling.

[0015] Furthermore, in step S1, the sodium source is one of sodium carbonate, sodium bicarbonate, and sodium acetate; and / or the manganese source is one of manganese dioxide, manganese sulfate, and manganese acetate; and / or the nickel source is one of nickel oxide, nickel nitrate, and nickel chloride; and / or the copper source is one of copper oxide and copper chloride; and / or

[0016] The ball milling is performed in an oxidizing atmosphere; and / or

[0017] The ball milling pressure is 0.018-0.022 MPa, and / or

[0018] Ball to material ratio is 7.5-8.5:1, and / or

[0019] The ball mill speed is 1300-1500 rpm.

[0020] Furthermore, the ball milling in step S1 is performed by plasma vibration ball milling, and each ball milling time is 15 to 25 minutes; and / or

[0021] The number of ball milling is 5 to 7 times; and / or

[0022] The interval between each two ball millings is 8 to 12 minutes.

[0023] Furthermore, the first sintering in step S2 includes a first pre-sintering and a first sintering, the temperature of the first pre-sintering is 500-600°C, and / or

[0024] The temperature of the first sintering is 850-950°C; and / or

[0025] The first pre-sintering time is 5.5 to 6.5 hours; and / or

[0026] The first sintering time is 7 to 9 hours; and / or

[0027] The heating rate of the first pre-sintering is 9-11°C / min; and / or

[0028] The heating rate of the first sintering is 4-6°C / min.

[0029] Furthermore, the mass of the sodium source added in step S2 is 0.5 wt% to 3 wt% of the sodium source in step S1.

[0030] Furthermore, the ball milling in step S2 is mechanical ball milling, and the ball-to-material ratio of the ball milling is 3 to 4:1, and / or

[0031] The ball milling speed is 350-450 rpm; and / or

[0032] Each ball milling time is 25 to 35 minutes, and / or

[0033] The number of ball milling is 3 to 5 times; and / or

[0034] The interval between each two ball millings is 4 to 6 minutes.

[0035] Furthermore, the secondary sintering in step S2 includes a second pre-sintering and a second sintering, and the temperature of the second pre-sintering is 750-850° C.; and / or

[0036] The temperature of the second sintering is 900-980°C; and / or

[0037] The second pre-sintering time is 4 to 5 hours, and / or

[0038] The second sintering time is 5 to 7 hours; and / or

[0039] The heating rate of the second pre-sintering is 4-6°C / min; and / or

[0040] The heating rate of the second sintering is 1.5-3°C / min.

[0041] The third aspect of the present application provides an application of the positive electrode material in the preparation of positive electrode sheets and / or sodium ion batteries.

[0042] The sodium ion battery consists of a positive electrode, a negative electrode, a separator and an electrolyte. The positive electrode is prepared from an O3 / O'3 hybrid phase layered oxide positive electrode material, and the negative electrode is prepared from a eucalyptus wood-based hard carbon material.

[0043] The present invention has the following beneficial effects:

[0044] In the O3 / O'3 hybrid layered oxide cathode material of the present invention, the phase composition, structural stability, capacity, energy density, and interfacial compatibility of the cathode material are adjusted by limiting the ratios of sodium, manganese, nickel, copper, and oxygen to improve the cycling performance of the cathode material. Furthermore, the O'3 and O3 structures in the cathode material of the present invention are staggered. When the material undergoes a phase change, the TMO2 (transition metal oxide layer) slides in different directions, and the grain boundaries between the different structures also inhibit the continuous slip of the TMO2 layer. Therefore, the hybrid phase structure in the cathode material of the present invention can enhance sodium ion diffusion and air stability, inhibit complex phase changes, and thereby improve the rate performance and cycling performance of the cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0046] Figure 1 This is the X-ray diffraction spectrum of the O3 / O'3 hybrid phase layered oxide positive electrode material prepared in Example 1.

[0047] Figure 2 This is the SEM image of the O3 / O'3 hybrid layered oxide positive electrode material prepared in Example 1.

[0048] Figure 3 This is a cycle performance diagram of a battery prepared using the O3 / O'3 hybrid layered oxide positive electrode material prepared in Example 1.

[0049] The purpose, features and advantages of this drawing will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative work are within the scope of protection of this application.

[0051] Obviously, the following descriptions are merely some examples or embodiments of the present application. Those skilled in the art can apply the present application to other similar scenarios without inventive effort. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in the present application, changes in design, manufacturing, or production based on the technical content disclosed in the present application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in the present application.

[0052] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0053] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0054] An embodiment of the first aspect of the present application provides a positive electrode material, including a layered oxide;

[0055] The layered oxide includes an O3 phase and an O'3 phase;

[0056] The molar fraction of the O3 phase is 65% to 85%, and the molar fraction of the O'3 phase is 15% to 35%.

[0057] The O'3 phase in the positive electrode material is a layered oxide (usually NaxMO2, where M is a transition metal such as Fe, Mn, Ni, Co or a combination thereof), whose crystal structure belongs to the hexagonal system (Hexagonal), and the space group is usually R-3m (the same as the O3 phase), but the local atomic arrangement or Na + The occupation mode is different from the standard O3 phase, and some Na + It may occupy tetrahedral sites and is usually formed at high Na content (x>0.9) or under specific synthesis conditions. The O'3 phase is usually more stable than the O3 phase.

[0058] The chemical formula of the layered oxide is NaMnxNiyCu Z O2, wherein 0.45≤x≤0.55, 0.3≤y≤0.42, 0.08≤z≤0.2, X+Y+Z=1, preferably, X=Y+Z, preferably, Y+Z=0.5;

[0059] Mn has a valence of +4, Ni has a valence of +2, and Cu has a valence of +2.

[0060] The sodium, manganese, nickel, copper and oxygen elements are derived from sodium carbonate, spherical manganese dioxide micron powder, nickel oxide nano powder and copper oxide nano powder.

[0061] The ratio of sodium, manganese, nickel, copper and oxygen in the cathode material of the present invention affects the phase composition, structural stability, capacity, energy density and interface compatibility of the cathode material.

[0062] (1) The sodium content determines the crystal structure type of the layered oxide cathode material. High sodium content (x>0.9) can form an O3 or O′3 structure, or an O3 / O′3 hybrid phase structure. At the same time, high sodium content layered oxide cathode materials have high structural stability and air stability.

[0063] (2) The synergistic effect of manganese and transition metal copper can optimize the structural stability of layered oxides and regulate the proportion of manganese to increase Mn 4+ The content of Mn 3+ The content of Mn 3+ The formation of Mn inhibits the Jahn-Teller effect and octahedral structure distortion. 2+ Improve the capacity of the positive electrode material and induce the layered oxide positive electrode material to have high capacity.

[0064] (3) Nickel plays a triple role in the O3 / O'3 hybrid layered oxide positive electrode, contributing to capacity, maintaining structural stability, and optimizing the sodium ion diffusion path, thereby increasing specific capacity and improving cycle and rate performance.

[0065] (4) Copper element Cu 2+ / Cu 3+ Redox couples exhibit high potentials in layered oxide cathode materials, providing capacity and thus high specific energy density.

[0066] (5) Oxygen in layered oxide positive electrode materials forms manganese-oxygen bonds and copper-oxygen bonds with transition metal manganese and copper, inhibiting O2p orbital hybridization, stabilizing lattice oxygen, reducing oxygen loss and promoting the redox activity of oxygen ions, thereby improving the capacity of the positive electrode material and the energy density of the battery.

[0067] In this embodiment, the O3 phase accounts for 65% to 85% of the positive electrode material; preferably, the O3 phase accounts for 69.8% to 79.5%, and more preferably, the O3 phase accounts for 71.9%. The O3 phase accounts for 15% to 35% of the positive electrode material; preferably, the O'3 phase accounts for 20.5% to 30.2%, and more preferably, the O'3 phase accounts for 28.1%. This ratio ensures uniform distribution of the O3 and O'3 phases within the material, further leveraging their synergistic effects and improving the material's electrochemical performance.

[0068] In this embodiment, the average particle size of the positive electrode material is 3 μm to 10 μm. Preferably, the average particle size of the positive electrode material is 5 μm. Such a particle size can improve the dispersion and contact of the positive electrode material in the battery, which is conducive to improving the battery's charge and discharge performance and cycle stability.

[0069] The O3 / O'3 hybrid phase layered oxide positive electrode material provided by the present invention exhibits excellent structural stability and outstanding cycle performance during the sodium ion intercalation and deintercalation process. For the O3 / O'3 hybrid phase layered oxide positive electrode material, the O'3 and O3 crystal structures are staggered. When the material undergoes a phase change, TMO2 slides in different directions (instead of continuously sliding in the same direction like in a single-phase material), and the grain boundaries between different structures also inhibit the continuous slip of the TMO2 layer. As sodium ions are extracted and intercalated, each phase structure in the O3 / O'3 hybrid phase layered oxide positive electrode material undergoes a transition from O to P type, accompanied by the coordinated sliding of the TMO2 layer in different directions. The transition from O3 to P3 phase can only be achieved by sliding two adjacent transition metal layers in different slip directions. There is a trend of transition from O type to P type when the charge and discharge voltage is below 3.5V, and there is a trend of transition from P type to O type when the charge and discharge voltage exceeds 3.5V. In O3 / O'3 hybrid layered oxide cathode materials, these phase transitions cannot occur simultaneously. This means that harmful phase transitions in O3 / O'3 hybrid layered oxide cathode materials may be hindered by the existing O'3 and O3 phase structures in the material. The transition metal layer cannot continuously slip, and the crystal structure is fixed by adjacent different phase structures, thus suppressing the phase transition and maintaining structural stability. Therefore, the structural constraint effect helps mitigate phase structure changes during sodium ion storage, which is beneficial for improving the electrochemical stability of O3 / O'3 hybrid layered oxide cathode materials.

[0070] The second aspect of the present application provides a method for preparing the positive electrode material, comprising the following steps:

[0071] The precursor is prepared by mixing a sodium source, a manganese source, a nickel source and a copper source through ball milling and then pressing.

[0072] S2: sintering the precursor once and twice;

[0073] During the secondary sintering process, a sodium source needs to be added for further ball milling.

[0074] The sodium source is one of sodium carbonate, sodium bicarbonate, and sodium acetate; the manganese source is one of manganese dioxide, manganese sulfate, and manganese acetate; the nickel source is one of nickel oxide, nickel nitrate, and nickel chloride; and the copper source is one of copper oxide and copper chloride.

[0075] Specifically, the method for preparing the positive electrode material comprises the following steps:

[0076] Sodium carbonate, spherical manganese dioxide micron powder, nickel oxide nanopowder, copper oxide nanopowder and ethanol are mixed and subjected to plasma vibration ball milling in a protective atmosphere to obtain a precursor;

[0077] The precursor is dried and pressed into tablets at a pressure of 16 MPa in a tablet press to obtain a sheet precursor;

[0078] The flake precursor is transferred to a muffle furnace and sintered once under air conditions to obtain a flake intermediate product;

[0079] The flaky intermediate product and sodium carbonate are added together into a mechanical ball mill for ball milling, and then subjected to secondary sintering and cooling.

[0080] The present invention provides a method for preparing an O3 / O'3 hybrid layered oxide cathode material, which is achieved through a preparation process of plasma ball milling, tableting, primary sintering, sodium supplementation, and secondary sintering. The method comprises:

[0081] The plasma ball milling process utilizes the synergistic effect of highly active ion particles and mechanical ball milling to increase surface defects and active sites of the positive electrode material, improve the chemical reaction activity and capacity of the positive electrode material, and at the same time promote the mass transfer process of the solid-phase reaction, reduce the synthesis temperature of the positive electrode material, and avoid abnormal grain growth.

[0082] Primary sintering is the cornerstone step in the preparation of O3 / O'3 hybrid phase layered oxide positive electrode materials. Its core function is to achieve the initial high-temperature solid-phase reaction of the raw materials and synthesize the target compound; through the nucleation and growth process of the primary sintering, micron-sized particles are formed; at the same time, it provides the necessary structural and chemical basis for subsequent sodium supplementation and secondary sintering.

[0083] The sodium replenishment process optimizes the performance of the O3 / O'3 hybrid layered oxide cathode material from the atomic scale to the macroscopic structure by precisely controlling the stoichiometric ratio, ensuring the integrity of the sodium sites, reducing side reactions, stabilizing the crystal framework, inhibiting phase changes, accelerating sodium ion diffusion, reducing polarization, passivating the material surface, and improving compatibility, thereby significantly improving capacity, cycle life, and rate performance.

[0084] Secondary sintering extends the high-temperature treatment time, reduces lattice defects, promotes the improvement of crystal structure, and improves crystallinity; it refines particles through the recrystallization process, regulates the morphology to form spherical particles, eliminates impurity phases, ensures uniform element distribution, and avoids phase change or structural collapse caused by local component segregation; secondary sintering can optimize the pore structure and improve ion / electronic conductivity; in addition, it can strengthen the grain boundary bonding force, enhance surface stability and interface compatibility, improve the crystallinity and structural stability of the material, thereby improving the specific capacity and cycle life of the battery.

[0085] In this embodiment, the protective atmosphere in step S1 is a mixture of argon and oxygen, the ball milling pressure is 0.018-0.022 MPa, the ball-to-material ratio is 7.5-8.5:1, and the ball milling speed is 1300-1500 rpm. The ball milling process in step S1 is plasma vibration ball milling for 15-25 minutes, resting for 8-12 minutes, and automatic cycle 5-7 times.

[0086] Furthermore, the atmosphere pressure of the plasma vibration ball mill is 0.02 MPa, the ball mill speed is 1400 rpm, the power frequency is 15 kHz, the plasma vibration ball mill is performed for 20 minutes, and then rested for 10 minutes, and the automatic cycle is repeated 6 times to make the particle size of each material reach less than 10 μm.

[0087] In this embodiment, the primary sintering in step S3 is to heat the material to 500-600°C at 9-11°C / min and perform pre-sintering for 5.5-6.5h; heat the material to 850-950°C at 4-6°C / min and perform sintering for 7-9h, and then cool the material to obtain a flaky intermediate product.

[0088] In this embodiment, the mass of the sodium carbonate in step S4 is 0.5wt% to 3wt% of the sodium carbonate in step S1; the balls in the mechanical ball mill are a mixture of 0.5mm diameter zirconia beads and 1mm diameter zirconia beads, with a mass ratio of 1:1; the ball-to-material ratio of the ball milling is 3-4:1, and the ball milling speed is 350-450rpm; the ball milling process is mechanical ball milling for 25-35 minutes, resting for 4-6 minutes, and automatic cycle 3-5 times. Preferably, the ball-to-material ratio is 3.5:1, the ball milling speed is 400rpm; the ball milling process is mechanical ball milling for 30 minutes, resting for 5 minutes, and automatic cycle 4 times.

[0089] In this embodiment, the secondary sintering in step S4 is to increase the temperature to 750-850°C at a rate of 4-6°C / min, hold the temperature for 4 hours, then increase the temperature to 900-980°C at a rate of 1.5-3°C / min and sinter for 5-7 hours, then cool the temperature to 750-850°C and hold the temperature for 3-5 hours. Preferably, the sintering is to increase the temperature to 800°C at a rate of 5°C / min, then increase the temperature to 950°C at a rate of 2°C / min and sinter at high temperature for 6 hours, then cool the temperature to 800°C and hold the temperature for 4 hours, and finally rapidly cool the product.

[0090] An embodiment of the third aspect of the present application provides an application of the positive electrode material in a sodium ion battery.

[0091] The sodium ion battery consists of a positive electrode, a negative electrode, a separator and an electrolyte. The positive electrode is prepared from an O3 / O'3 hybrid phase layered oxide positive electrode material, and the negative electrode is prepared from a eucalyptus wood-based hard carbon material.

[0092] Example 1

[0093] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0094] (1) Four raw materials, Na2CO3, MnO2, NiO and CuO, were placed in a plasma ball mill together with ethanol, wherein the molar ratio of Mn:Ni:Cu was 5:3:2, the pressure of the mixed atmosphere of argon and oxygen was 0.02 MPa, the ball milling speed was 1400 rpm, the power supply frequency was 15 kHz, and the plasma vibration ball milling was performed for 20 minutes, followed by 10 minutes of rest, and the automatic cycle was repeated 6 times to obtain a precursor with a particle size of less than 5 μm.

[0095] (2) drying the precursor obtained in step (1), and then pressing it into tablets in a tablet press at a pressure of 16 MPa;

[0096] (3) The sheet-like precursor obtained in step (2) is placed in a muffle furnace for a single sintering; the single sintering includes a first pre-sintering and a first high-temperature sintering, and after each sintering is completed, it is naturally cooled to room temperature (25°C) to obtain a sheet-like intermediate. The first pre-sintering temperature is 550°C, the time is 6 hours, and the heating rate is 10°C / min; the first high-temperature sintering temperature is 900°C, the time is 8 hours, and the heating rate is 5°C / min;

[0097] (4) The flaky intermediate product obtained in step (3) and sodium carbonate are placed in a planetary ball mill. Zirconia beads with a diameter of 0.5 mm and 1 mm are added in a mass ratio of 1:1, and the mass ratio of the zirconia balls to the material is 3.5:1. Ethanol is added to cover the mixture and the zirconia beads and ball milled. The ball milling process is mechanical ball milling for 30 minutes, resting for 5 minutes, and automatic cycle 4 times. The mass of the sodium carbonate is 3% of the mass of the sodium carbonate in step (1).

[0098] (5) The mixture obtained in step (4) is subjected to secondary sintering, which includes a first pre-sintering and a second high-temperature sintering. The first pre-sintering is performed by heating the temperature to 800°C at a rate of 5°C / min for 4 hours, and the second high-temperature sintering is performed by heating the temperature to 950°C at a rate of 2°C / min for 6 hours, then cooling the temperature to 800°C and keeping the temperature for 4 hours, and finally rapidly cooling to obtain the product.

[0099] The crystal structure of O3 / O'3 hybrid layered oxide cathode materials was analyzed using X-ray diffraction technology. Figure 1 As shown, the main diffraction peaks of the cathode material are consistent with those of the O3 and O'3 standard cards, indicating good crystallinity. The small amount of copper ions exists mostly as a solid solution in the lattice, without affecting the crystal structure. The O3 phase accounts for 71.9% of the material, and the O'3 phase accounts for 28.1%.

[0100] Scanning electron microscopy was used to investigate the morphology of O3 / O'3 hybrid layered oxide cathode materials. Figure 2 As shown, the positive electrode material is in the form of spherical particles with an average particle diameter of 3 to 10 μm.

[0101] The O3 / O'3 hybrid layered oxide cathode material, PVDF, and acetylene black with a mass ratio of 8:1:1 were added to N-methylpyrrolidone solution (NMP), stirred evenly to form a slurry, and after coating, placed in a vacuum drying oven at 120°C for 12 hours to obtain a cathode sheet, which was then made into a CR2032 button battery. The battery performance was tested under the following test conditions: the current density was 0.1C~5C (1C=150mAg -1 ), the voltage window is 2-4V. The test results show that at a current density of 0.1C, the battery's first discharge capacity is 126.8mAh / g; at a current density of 5C, the battery's discharge capacity is 88.5mAh / g; at a current density of 1C, the battery's first discharge capacity is 103.2mAh / g, and the capacity retention rate after 200 cycles is 95.5%. Figure 3 shown.

[0102] Example 2

[0103] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof. The preparation method is basically the same as the preparation method in Example 1, with the only difference being that in step (1), the molar ratios of manganese, nickel, and copper in the precursor are different, and the mass of sodium carbonate in step (4) is 2% of the mass of sodium carbonate in step (1).

[0104] The positive electrode sheet and battery assembly in Example 1 were assembled, and the performance test method was basically the same as that in Example 1. At a current density of 1C, the initial discharge capacity of the battery in this example was 102.5mAh / g, and the capacity retention rate after 200 cycles was 80.3%.

[0105] Example 3

[0106] The present invention provides an O3 / O'3 hybrid layered oxide cathode material and a preparation method thereof. The preparation method is substantially the same as that in Example 1, except that in step (1), the molar ratio of Mn:Ni:Cu in the precursor is 5:3.5:1.5.

[0107] The positive electrode sheet and battery assembly in Example 1 were assembled, and the performance test method was basically the same as that in Example 1. At a current density of 1C, the initial discharge capacity of the battery in this example was 102.1 mAh / g, and the capacity retention rate after 200 cycles was 82.5%.

[0108] Example 4

[0109] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof. The preparation method is basically the same as the preparation method in Example 1, with the only difference being that in step (3), the temperature is raised to 500°C at 9°C / min for pre-sintering for 6.5 hours; and then the temperature is raised to 950°C at 6°C / min for sintering for 7 hours.

[0110] The positive electrode sheet and battery assembly in Example 1 were assembled, and the performance test method was basically the same as that in Example 1. At a current density of 1C, the initial discharge capacity of the battery in this example was 101.6 mAh / g, and the capacity retention rate after 200 cycles was 84.7%.

[0111] Example 5

[0112] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof. The preparation method is basically the same as the preparation method in Example 1, with the only difference being that in step (5), the temperature is raised to 750°C at 4°C / min and pre-sintered for 4 hours, then raised to 900°C at 3°C / min and sintered for 7 hours, and then cooled to 750°C and kept warm for 5 hours.

[0113] The positive electrode sheet and battery assembly in Example 1 were assembled, and the performance test method was basically the same as that in Example 1. At a current density of 1C, the initial discharge capacity of the battery in this example was 101.3 mAh / g, and the capacity retention rate after 200 cycles was 85.2%.

[0114] Comparative Example 1

[0115] The present invention provides an O3 layered oxide positive electrode material and a preparation method thereof. The preparation method is substantially the same as the preparation method in Example 1, except that in step (1), the raw materials are Na2CO3, Li2CO3, MnO2, and NiO, and the molar ratio of manganese, lithium, and nickel in the precursor is 5:1:4. The mass of sodium carbonate in step (4) is 1% of the mass of the sodium carbonate in step (1).

[0116] The positive electrode sheet and battery assembly were assembled according to Example 1, and the performance test method was basically the same as Example 1. At a current density of 1C, the initial discharge capacity of the battery was 108.7mAh / g, and the capacity retention rate after 200 cycles was 69.6%.

[0117] Compared to Example 1, the cycling performance of the cathode material deteriorated significantly, primarily due to the crystal structure, the absence of copper, and the introduction of lithium. The layered oxide cathode material provided in Comparative Example 1 has a single-phase O3 structure. During sodium storage, the material undergoes a phase transition, with TMO2 continuously sliding in the same direction. The lack of O′3 phase and grain boundary hindrances leads to poor structural stability and, consequently, poor cycling performance.

[0118] In addition, in the embodiment of the present invention, the synergistic effect of manganese element and transition metal copper can optimize the structural stability of the O3 / O′3 phase layered oxide positive electrode material, inhibit the Jahn-Teller effect and octahedral structure distortion, and improve the cycle performance of the positive electrode material.

[0119] Comparative Example 2

[0120] The present invention provides an O3 / O'3 hybrid phase layered oxide cathode material and a preparation method thereof. The preparation method is substantially the same as that in Example 1, with the only difference being that mechanical ball milling is used in step (1).

[0121] The positive electrode sheet and battery were assembled according to Example 1. The performance test method was basically the same as that of Example 1. At a current density of 0.1C, the initial discharge capacity of the battery was 120.5mAh / g.

[0122] While mechanical ball milling in Comparative Example 2 can also achieve uniform mixing of the raw materials and reduce particle size, it cannot, like plasma vibration ball milling, leverage the synergistic effect of highly active plasma particles and mechanical milling to increase surface defects and active sites in the cathode material, thereby improving the chemical reactivity and capacity of the cathode material. Therefore, the electrochemical performance of the O3 / O'3 hybrid layered oxide cathode material prepared using mechanical ball milling is relatively poor.

[0123] Comparative Example 3

[0124] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof. The preparation method is substantially the same as the preparation method in Example 1, with the only difference being that step (2) is missing in the entire preparation process.

[0125] The positive electrode sheet and battery were assembled according to Example 1. The performance test method was basically the same as that of Example 1. At a current density of 0.1C, the initial discharge capacity of the battery was 121.5mAh / g.

[0126] Comparative Example 4

[0127] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof. The preparation method is substantially the same as that in Example 1, except that sodium carbonate is not added in step (3).

[0128] The positive electrode sheet and battery assembly were assembled according to Example 1, and the performance test method was basically the same as Example 1. At a current density of 1C, the initial discharge capacity of the battery was 87.0mAh / g. After 100 cycles, the capacity retention rate was 88.5%.

[0129] Comparative Example 5

[0130] The present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof. The preparation method is substantially the same as that in Example 1, except that steps (4) and (5) are missing from the entire preparation process.

[0131] The positive electrode sheet and battery were assembled according to Example 1. The performance test method was basically the same as that of Example 1. At a current density of 0.1C, the initial discharge capacity of the battery was 102.1mAh / g.

[0132] In summary, the present invention provides an O3 / O'3 hybrid phase layered oxide positive electrode material and a preparation method thereof, which first utilizes a plasma ball milling process to prepare a precursor with a suitable particle size; then the precursor is subjected to low-temperature pre-sintering and high-temperature sintering in sequence, and a flaky intermediate is obtained by tableting; then the flaky intermediate is mixed with sodium carbonate in a mechanical ball mill, and subjected to a second high-temperature sintering to obtain a spherical O3 / O'3 hybrid phase layered oxide positive electrode material with an average particle diameter of 3 to 10 μm. In the O3 / O'3 hybrid phase layered oxide positive electrode material of the present invention, the O'3 and O3 structures are staggered. When the material undergoes a phase change, TMO2 slides in different directions (instead of continuously sliding in a uniform direction like in a single-phase material), and the grain boundaries between different structures also inhibit the continuous sliding of the TMO2 layer. Therefore, the hybrid phase structure can enhance sodium ion diffusion and air stability, inhibit complex phase changes, and thereby improve the rate performance and cycle performance of the positive electrode material.

[0133] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode material, characterized in that including layered oxides; The layered oxide includes an O3 phase and an O'3 phase; The molar fraction of the O3 phase is 65% to 85%, and the molar fraction of the O'3 phase is 15% to 35%.

2. The positive electrode material according to claim 1, characterized in that The chemical formula of the layered oxide is NaMnxNiyCu Z O2, where 0.45≤x≤0.55, 0.3≤y≤0.42, 0.08≤z≤0.

2.

3. A method for preparing the positive electrode material according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1: Sodium source, manganese source, nickel source and copper source are mixed by ball milling and then pressed to prepare a precursor; S2: sintering the precursor once and twice; During the secondary sintering process, a sodium source needs to be added for further ball milling.

4. The method for preparing a positive electrode material according to claim 3, characterized in that in step S1, the sodium source is one of sodium carbonate, sodium bicarbonate, and sodium acetate; and / or the manganese source is one of manganese dioxide, manganese sulfate, and manganese acetate; and / or the nickel source is one of nickel oxide, nickel nitrate, and nickel chloride; and / or the copper source is one of copper oxide and copper chloride; and / or The ball milling is performed in an oxidizing atmosphere; and / or The ball milling pressure is 0.018-0.022 MPa, and / or Ball to material ratio is 7.5-8.5:1, and / or The ball mill speed is 1300-1500 rpm.

5. The method for preparing the positive electrode material according to claim 3, wherein: The ball milling in step S1 is performed by plasma vibration ball milling, and each ball milling time is 15 to 25 minutes; and / or The number of ball milling is 5 to 7 times; and / or The interval between each two ball millings is 8 to 12 minutes.

6. The method for preparing the positive electrode material according to claim 3, wherein: The first sintering in step S2 includes a first pre-sintering and a first sintering, wherein the temperature of the first pre-sintering is 500-600°C, and / or The temperature of the first sintering is 850-950°C; and / or The first pre-sintering time is 5.5 to 6.5 hours; and / or The first sintering time is 7 to 9 hours; and / or The heating rate of the first pre-sintering is 9-11°C / min; and / or The heating rate of the first sintering is 4-6°C / min.

7. The method for preparing the positive electrode material according to claim 3, wherein: The mass of the sodium source added in step S2 is 0.5 wt % to 3 wt % of the sodium source in step S1.

8. The method for preparing the positive electrode material according to claim 3, wherein: The ball milling in step S2 is mechanical ball milling, and the ball-to-material ratio of the ball milling is 3 to 4:1, and / or The ball milling speed is 350-450 rpm; and / or Each ball milling time is 25 to 35 minutes, and / or The number of ball milling is 3 to 5 times; and / or The interval between each two ball millings is 4 to 6 minutes.

9. The method for preparing the positive electrode material according to claim 3, wherein: The secondary sintering in step S2 includes a second pre-sintering and a second sintering. The temperature of the second pre-sintering is 750-850° C.; and / or The temperature of the second sintering is 900-980°C; and / or The second pre-sintering time is 4 to 5 hours, and / or The second sintering time is 5 to 7 hours; and / or The heating rate of the second pre-sintering is 4-6°C / min; and / or The heating rate of the second sintering is 1.5-3°C / min.

10. Use of the positive electrode material according to any one of claims 1 to 2 in the preparation of positive electrode sheets and / or sodium ion batteries.

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