A lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure, its preparation method, and a lithium-ion battery.

Abstract

This invention belongs to the field of lithium battery technology, and relates to a lithium-rich manganese-based cathode material with a pure-phase O2 type layered crystal structure, its preparation method, and a lithium-ion battery. The chemical composition of the cathode material is Li. 1+x Mn y Ni z Co w The cathode material exhibits a pure-phase diffraction characteristic of a single O2-type layered structure, with its X-ray diffraction pattern showing no (020) crystal plane characteristic diffraction peaks corresponding to the Li2MnO3 structure in the range of 2θ = 20°–25°. This invention avoids the formation of the Li2MnO3 superlattice phase in traditional lithium-rich manganese-based materials, enabling the lithium-rich manganese-based cathode material to exhibit a single O2-type layered crystal structure. This achieves the construction of a uniform pure-phase system, which is beneficial for improving the specific capacity and cycle stability of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and relates to a lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The rapid development of new energy vehicles and large-scale energy storage technologies has put forward higher requirements for the energy density and cycle life of lithium-ion batteries. As an important part of lithium-ion batteries, the crystal structure stability and electrochemical performance of cathode materials directly affect the overall performance of the battery. Lithium-rich manganese-based layered oxide cathode materials (LRM, xLi2MnO3·(1-x)LiMO2, 0<x<1, M is Ni, Co, Mn) are considered to be the key materials for next-generation high-energy-density lithium-ion batteries due to their high theoretical specific capacity (>250 mAh / g) and high working voltage.

[0003] According to different oxygen atom stacking modes, lithium-rich manganese-based cathode materials can be divided into O3-type and O2-type structures. In the O3-type traditional lithium-rich manganese-based materials, problems such as transition metal migration, structural phase transformation, and oxygen release are likely to occur during the cycling process, resulting in voltage decay and capacity decay. In contrast, the O2-type structure exhibits better electrochemical performance due to its unique oxygen atom stacking mode (ABAC) that can form more open ion channels, and thus has more practical application value.

[0004] Currently, the preparation of O2-type lithium-rich manganese-based cathode materials mostly adopts the ion exchange method, that is, a P2-type sodium battery layered oxide precursor is prepared in advance, and then the O2-type lithium-rich manganese-based cathode material is obtained through Li + / Na + ion exchange. However, this preparation process is complex and has many influencing factors, and the crystal structures of the materials prepared under different process conditions vary greatly. Currently, the O2-type lithium-rich manganese-based cathode materials prepared by the existing technology usually show superlattice structure characteristic peaks of the Li2MnO3 component in the range of 2θ = 20° - 25° in the X-ray diffraction (XRD) pattern. This indicates that there is a traditional composite structure in the material, and such a traditional structure is still extremely prone to layered structure slip and irreversible phase transformation during charge and discharge, especially at high voltages, resulting in rapid capacity decay.

[0005] Therefore, it is of great significance to develop a method for preparing a pure-phase O2-type lithium-rich manganese-based cathode material without impurities such as Li2MnO3. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure and a preparation method thereof, so as to overcome the deficiencies of the prior art.

[0007] The present invention employs the following technical solutions to achieve its objective: The first aspect of the present invention provides a lithium-rich manganese-based cathode material having a pure-phase O2-type layered crystal structure, wherein the cathode material has a chemical composition of Li. 1+x Mn y Ni z Co w O2, 0<x≤0.5, 0.3≤y≤0.7, 0.05≤z≤0.3, 0.05≤w≤0.4; The cathode material exhibits pure phase diffraction characteristics of a single O2-type layered structure. No characteristic diffraction peaks corresponding to the Li2MnO3 structure were observed in its X-ray diffraction (XRD) pattern. In particular, no characteristic diffraction peaks of the Li2MnO3 phase (020) crystal plane were observed in the range of 2θ=20°-25°.

[0008] Preferably, in the XRD pattern of the cathode material, the peak intensity ratio of the (002) crystal plane diffraction peak to the (104) crystal plane diffraction peak is I. (002) / I (104) ≥5. Higher I (002) / I (104) The ratio indicates that the material has a low degree of cation mixing and a high degree of layered structural order, which is beneficial to improving the structural stability of the material during cycling.

[0009] Preferably, the average grain size of the cathode material along the normal direction of the (002) crystal plane is 20~60 nm, calculated based on the half-width at half-maximum of the diffraction peak of the (002) crystal plane and in conjunction with the Scherrer formula.

[0010] The cathode material has a hexagonal crystal system with space group P63mc, exhibiting typical O2-type layered crystal structure characteristics and lacking the characteristic diffraction peaks of the Li2MnO3 structure. The Li2MnO3 superlattice phase is prone to oxygen release and transition metal migration during high-voltage activation, inducing an irreversible phase transition from layered structure to spinel or rock salt structure. This is considered one of the important reasons for voltage decay and structural degradation in traditional lithium-rich manganese-based cathode materials. This invention eliminates this structural unit, suppressing the irreversible phase transition at the crystal structure level, thereby significantly improving the material's structural stability and cycle performance.

[0011] A second aspect of the present invention provides a method for preparing a lithium-rich manganese-based cathode material having a pure-phase O2-type layered crystal structure, comprising the following steps: (1) Sodium source, nickel source, cobalt source and manganese source are mixed and crushed to the submicron level, and then sintered in two steps to obtain P2 phase sodium-electric layered oxide precursor; (2) The sodium-ion layered oxide precursor is mixed with multi-component lithium salt and ion exchange is carried out by sintering to obtain lithium-rich manganese-based cathode material with pure phase O2 type layered crystal structure.

[0012] In step (1), the sodium source, nickel source, cobalt source, and manganese source are weighed according to the chemical composition of the final cathode material. The sodium source is selected from inorganic compounds of sodium, including but not limited to one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide; the nickel source is selected from inorganic compounds of nickel, including but not limited to one or more of nickel oxide, nickel hydroxide, and nickel carbonate; the cobalt source is selected from inorganic compounds of cobalt, including but not limited to one or more of cobalt oxide, cobalt hydroxide, and cobalt carbonate; and the manganese source is selected from inorganic compounds of manganese, including but not limited to one or more of manganese dioxide, manganese oxide, and manganese carbonate.

[0013] The mixing and pulverizing in step S1 involves mixing equipment including, but not limited to, one or more of the following: a mixer, a ball mill, a fluidized bed mixer, and a drum mixer. Mixing methods include solid-phase mixing or liquid-phase mixing. Liquid-phase mixing requires the addition of a liquid medium such as water or an alcohol solvent. If liquid-phase mixing is chosen, subsequent drying in an oven is required.

[0014] Preferably, the mixing and pulverizing is performed using a ball mill. The ball milling speed is 100~500 rpm, and the ball milling time is 6~15 h. The ball milling process can be performed using two methods: solid-phase ball milling or liquid-phase ball milling: (1) Solid-phase ball milling: The weighed sodium source, nickel source, cobalt source, manganese source and ball milling media are directly added to the ball milling equipment for ball milling. (2) Liquid-phase ball milling: The weighed raw materials, ball milling media and liquid media are added to the ball milling equipment for ball milling. After the liquid-phase ball milling is completed, the ball milling slurry needs to be dried to remove the liquid media. The ball milling media is preferably zirconia ball milling beads; the liquid media is preferably water and / or alcohol solvents, and the alcohol solvents are further preferably one or more of ethanol, methanol and isopropanol.

[0015] Further preferably, the ball milling process is solid-phase ball milling.

[0016] Submicron size refers to a particle size range of 0.1 μm to 1 μm. Preferably, after refining the raw materials to the submicron scale, the particle size distribution satisfies: D10 < 0.32 μm, 0.35 μm ≤ D50 ≤ 1.0 μm, D90 ≤ 1.2 μm, and the particle size distribution span K90 = (D90 - D10) / D50 ≥ 1.2. Refining the sodium, nickel, cobalt, and manganese sources to the submicron scale with specific parameters can significantly improve the dispersion uniformity and solid-phase reaction activity of each raw material. During subsequent high-temperature calcination, the highly active submicron particles can participate more fully and uniformly in the crystal structure construction, avoiding side reactions caused by local uneven concentration, thereby suppressing the formation of impurity phases from the source. This yields a P2 phase sodium-electric layered oxide precursor with uniform composition distribution and extremely high crystallinity, laying the foundation for the subsequent ion exchange preparation of pure phase O2 type materials.

[0017] For the sintering process in step S1, either a muffle furnace or a tube furnace can be selected as the sintering equipment.

[0018] Preferably, in step S1, the two-step sintering is carried out in an air or oxygen atmosphere; the temperature of the first pre-sintering step is 500~650℃, and the time is 5~8 h; the temperature of the second sintering step is 700~950℃, and the time is 0.5~12 h. Examples of the first pre-sintering temperatures include 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, and 650℃, and examples of sintering times include 5, 6, 7, and 8 h. The second-step sintering temperature is 700, 720, 740, 760, 780, 800, 820, 840, 860, 880, 900, 920, and 950℃, with sintering times of 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 hours. The heating rate for the two-step sintering process is 3~7℃ / min. The core function of pre-sintering is to allow the sodium source and transition metal source to decompose slowly, forming uniform crystal nuclei and avoiding the rapid decomposition and component segregation of raw materials caused by the first-step high-temperature sintering. The second-step high-temperature sintering promotes preferential grain growth and a denser crystal structure. If direct high-temperature sintering is performed, or if the sintering temperature is too low or the sintering time is insufficient, it can easily lead to poor precursor crystallinity or the appearance of impurity phases, directly affecting the purity of the final ion-exchange product.

[0019] In a further preferred embodiment, in the two-step sintering process, the temperature of the first pre-sintering step is 500~580 ℃ and the time is 5~7 h; the temperature of the second sintering step is 850~930 ℃ and the time is 2~5 h.

[0020] Preferably, the multi-component lithium salt is a mixture of at least two of lithium hydroxide, lithium carbonate, lithium chloride, lithium nitrate, and lithium bromide. Single lithium salts have fixed melting points and decomposition temperatures, and during ion exchange, they are prone to problems such as excessively fast or slow lithium source supply, leading to incomplete local ion exchange, structural defects, or impurity phase formation. Multi-component lithium salts can form a eutectic system under high-temperature conditions, creating a uniform liquid phase environment during heat treatment, providing a more stable and continuous lithium-ion supply, and ensuring the Li-144 lithium salt's stability. + / Na + Ion exchange occurs uniformly and completely throughout the entire material particle, effectively suppressing structural defects and the formation of impurity phases.

[0021] Preferably, in the multi-component lithium salt, the mass percentage of any single-component lithium salt is ≥10%. If the mass percentage of a single-component lithium salt is too low, it is not conducive to forming a stable eutectic system, leading to uneven ion exchange. More preferably, the mass percentage of any single-component lithium salt is 30-70%.

[0022] Further preferably, the multi-component lithium salt is a mixture of lithium chloride and lithium nitrate, with a mass ratio of lithium chloride to lithium nitrate of 1:0.8~1.2.

[0023] Preferably, the mass ratio of the sodium-ionized layered oxide precursor to the multi-component lithium salt is 1:2 to 8.

[0024] The sintering equipment used for sintering ion exchange treatment can be a muffle furnace or a tube furnace. Preferably, the atmosphere for sintering ion exchange treatment is selected from air, argon, or an argon-hydrogen mixture; the sintering temperature for sintering ion exchange treatment is 200~500 ℃, and the sintering time is 3~24 h.

[0025] After sintering and ion exchange treatment, post-treatment is performed, which includes washing, filtering and drying. The solvent used for washing is one or more of water, ethanol, acetone and methanol. The drying is carried out using an oven or dryer, and the drying temperature is between 50-200 ℃.

[0026] This invention prepares an O2-type lithium-rich manganese-based cathode material with a specific XRD diffraction structure by mixing and pulverizing raw materials to the submicron level, performing two-step sintering and ion exchange, and controlling the synthesis conditions. This preparation method avoids the formation of the Li2MnO3 superlattice phase in traditional lithium-rich manganese-based materials, resulting in a single O2-type layered crystal structure, thus achieving the construction of a uniform pure phase system.

[0027] A third aspect of the present invention provides a lithium-ion battery comprising a positive electrode, the positive electrode comprising the aforementioned lithium-rich manganese-based positive electrode material having a pure-phase O2-type layered crystal structure. Using the lithium-rich manganese-based positive electrode material with a pure-phase O2-type layered crystal structure provided by the present invention to prepare the positive electrode of a lithium-ion battery is beneficial for improving battery capacity and cycle stability.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure. This material does not have the Li2MnO3 superlattice phase found in traditional lithium-rich manganese-based materials, thus suppressing the occurrence of irreversible phase transitions from the root of the crystal structure and achieving a breakthrough in the core structure.

[0029] 2. This invention significantly improves the dispersion uniformity and reactivity of raw materials by refining them to the submicron scale, enabling them to participate more fully and uniformly in crystal structure construction during subsequent high-temperature calcination, thus suppressing the formation of impurity phases at the source. Simultaneously, a two-step sintering process successfully constructs a P2-phase sodium-ion layered precursor with near-perfect crystallinity, laying the foundation for the superior performance of the final material. The introduction of a multi-component lithium salt system during ion exchange provides a more stable and continuous lithium-ion supply environment compared to traditional single lithium sources, promoting the uniform embedding of lithium ions in the layered structure and effectively avoiding problems such as uneven local reactions and incomplete lithium source decomposition, further reducing structural defects and impurity phase content. Based on these synergistic effects, this invention avoids the formation of the Li2MnO3 superlattice phase in traditional lithium-rich manganese-based materials, resulting in a single O2-type layered crystal structure and achieving the construction of a structurally uniform pure-phase system.

[0030] 3. The pure-phase O2 type layered structure effectively suppresses the migration of the transition metal layer and the slippage of the layered structure during charging and discharging, greatly reducing the probability of irreversible phase transition and significantly improving the overall structural stability of the material; the lithium-ion battery prepared by the pure-phase O2 type lithium-rich manganese-based cathode material of this invention has higher first-cycle capacity and better cycle retention rate.

[0031] 4. In the preparation process of this invention, solid-phase ball milling is preferably used to mix the raw materials, and the two-step sintering temperature is precisely controlled, which is beneficial for constructing a precursor with more perfect crystallinity. In the ion exchange process, a mixed system of lithium chloride and lithium nitrate is preferably used to provide a more suitable eutectic liquid phase environment and ion exchange kinetics, achieving uniform and complete ion exchange, thereby effectively avoiding the formation of structural defects and impurity phases. Further control of the preparation process and parameters is beneficial for preparing O2-type lithium-rich manganese-based cathode materials with better performance, improving battery specific capacity and cycle stability.

[0032] 5. The preparation method of the present invention has controllable parameters, low raw material cost, and does not require the use of complex production equipment. The overall process is simple and very suitable for large-scale industrial production, with extremely high commercial transformation and application prospects. Attached Figure Description

[0033] Figure 1 The XRD pattern of the O2-type lithium-rich manganese-based cathode material prepared in Example 1; Figure 2 The image shows a scanning electron microscope (SEM) image of the O2-type lithium-rich manganese-based cathode material prepared in Example 1. Figure 3 The XRD pattern of the O2-type lithium-rich manganese-based cathode material prepared in Comparative Example 2; Figure 4 The XRD pattern of the O2-type lithium-rich manganese-based cathode material prepared in Comparative Example 5; Figure 5 The first charge-discharge curve of the battery assembled with the O2-type lithium-rich manganese-based cathode material in Example 1 at a current density of 0.1C is shown. Figure 6 The first charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material for Comparative Example 1 at a current density of 0.1C. Figure 7 The first charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material for Comparative Example 2 at a current density of 0.1C. Figure 8 The first charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material for Comparative Example 4 at a current density of 0.1C. Figure 9 The first charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material for Comparative Example 5 at a current density of 0.1C. Figure 10 The first charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material of Comparative Example 6 at a current density of 0.1C. Figure 11 The first charge-discharge curve of the battery assembled with the lithium-rich manganese-based cathode material of Comparative Example 7 at a current density of 0.1C. Detailed Implementation

[0034] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two or more types, and can be two, three, four, five, or more.

[0035] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0036] XRD patterns were obtained using a Bruker D8 DISCOVER X-ray diffractometer (Germany), with CuK wavelengths of 0.154 Å used for the measurements. α As a radiation source, the operating voltage is 40 kV, the operating current is 40 mA, the scanning angle range is 10°-80°, and the total scanning time is 14 min.

[0037] Example 1 The lithium-rich manganese-based cathode material provided in this embodiment has the chemical formula Li. 1.2 Mn 0.5 Ni 0.2 Co 0.3 The specific preparation process for O2 is as follows: S1. Weigh out Na2CO3, cobalt oxide, nickel oxide, and manganese oxide according to the stoichiometric ratio of the sodium-ionized layered oxide precursor and mix them, with the mass of each raw material being 3.52 g, 2.29 g, 1.42 g, and 4.13 g, respectively. Add the mixed raw materials and zirconia grinding balls to a ball mill jar at a mass ratio of 1:5 and ball mill at 300 rpm for 8 h to ensure that the raw materials are fully mixed and pulverized to the submicron level, obtaining the precursor powder. Through particle size testing, the precursor raw materials at this time have D10=0.293 μm, D50=0.463 μm, D90=0.977 μm, and K90=(D90-D10) / D50=1.477.

[0038] S2. The precursor powder was calcined in a muffle furnace, heated to 500 °C for 6 h at a heating rate of 5 °C / min in air atmosphere, and then heated to 900 °C for 3 h at a heating rate of 5 °C / min to obtain the sodium-electric layered oxide precursor.

[0039] S3. Mix the precursor, LiCl, and LiNO3 at a mass ratio of 1:2:2. Place the mixture in a muffle furnace and calcine it at 400 °C for 2 hours in air at a heating rate of 5 °C / min. + / Na +Ion exchange treatment. After calcination, the material is added to deionized water and filtered. The filtered residue is then dried in an oven at 200 °C for 12 h to obtain O2-type lithium-rich manganese-based ternary cathode material.

[0040] The XRD diffraction pattern of the O2-type lithium-rich manganese-based cathode material prepared in this embodiment is shown in [reference needed]. Figure 1 Its XRD diffraction pattern shows obvious diffraction peaks at 2θ of approximately 18°-19°, 36°-38°, 44°-46°, 64°-66°, and 68°-70°, which can be attributed to the (002), (104), (106), (110), and (112) crystal planes of the layered structure, respectively. Furthermore, the positions and relative intensities of these diffraction peaks are similar to those of Li. 0.45 Mn 1.05 The results are largely consistent with the O2 standard card, indicating that the obtained material exhibits typical O2-type layered crystal structure characteristics. Its crystal structure belongs to the hexagonal crystal system, and its crystallographic features are consistent with the structural model of space group P63mc. Furthermore, no (020) superlattice characteristic diffraction peaks belonging to the Li2MnO3 phase were observed in the 2θ range of approximately 20°-25° (in XRD test data, when the intensity of diffraction peaks in the 20°-25° range is <1% relative to the main peak intensity, it can be determined that no corresponding diffraction peak was observed). In addition, no characteristic diffraction peaks such as (003) corresponding to the traditional O3-type layered structure appeared in the spectrum, indicating that the prepared material exhibits pure-phase diffraction characteristics of a single O2-type layered crystal structure. In the XRD pattern of the material, the intensity ratio of the characteristic diffraction peaks of the (002) crystal plane to those of the (104) crystal plane is 10.76. Based on the half-width at half-maximum (WHM) of the diffraction peaks of the (002) crystal plane and the Scherrer formula, the average grain size of the material along the normal direction of the (002) crystal plane is approximately 41 nm.

[0041] The scanning electron microscope image of the O2-type lithium-rich manganese-based cathode material prepared in this embodiment is shown below. Figure 2 As can be seen from the scanning electron microscope images, the O2-type lithium-rich manganese-based cathode material prepared in this embodiment has an irregular granular morphology. The particle size is mainly distributed in the submicron to several micrometer range. Some larger particles are formed by the accumulation of fine grains. The overall particle distribution is relatively uniform, and no obvious bulk sintered structure was observed.

[0042] Example 2 The only difference between Example 2 and Example 1 is that step S1 in Example 2 uses liquid-phase ball milling; the specific steps are as follows: S1. Weigh out Na2CO3, cobalt oxide, nickel oxide, and manganese oxide according to the stoichiometric ratio of the sodium-ionized layered oxide precursor and mix them. Add the mixed raw materials and zirconium oxide grinding balls to a ball milling jar at a mass ratio of 1:5. Add anhydrous ethanol as the liquid medium and ball mill at 300 rpm for 8 hours to fully mix the raw materials and refine them to the submicron level. After ball milling, place the slurry in a 100 ℃ forced-air oven and dry it for 2 hours to obtain a uniformly mixed precursor powder. Steps S2 and S3 are the same as in Example 1.

[0043] Example 3 The difference between Example 3 and Example 1 is only that: in Example 3, step S2 is a sintering process in which the temperature is raised to 600°C for 6 hours in air at a heating rate of 5°C / min, and then raised to 800°C for 3 hours at a heating rate of 5°C / min. The remaining steps are the same as in Example 1, and O2-type lithium-rich manganese-based cathode material is prepared.

[0044] Example 4 The only difference between Example 4 and Example 1 is that in step S3 of Example 4, lithium bromide and anhydrous lithium nitrate are used as lithium salts with a mass ratio of precursor:LiBr:LiNO3=1:2:2; the remaining steps are the same as in Example 1, and O2-type lithium-rich manganese-based cathode material is prepared.

[0045] Example 5 The lithium-rich manganese-based cathode material provided in this embodiment has the chemical formula Li. 1.2 Mn 0.6 Ni 0.2 Co 0.2 The specific preparation process for O2 is as follows: S1. Weigh out Na2CO3, cobalt oxide, nickel oxide, and manganese oxide according to the stoichiometric ratio of the sodium-ionized layered oxide precursor and mix them, with the mass of each raw material being 3.55 g, 1.53 g, 1.43 g, and 4.99 g, respectively. Add the mixed raw materials and zirconia grinding balls to a ball mill jar at a mass ratio of 1:5 and ball mill at 300 rpm for 8 h to ensure that the raw materials are fully mixed and pulverized to the submicron level, obtaining the precursor powder. Through particle size testing, the precursor raw materials at this time have D10=0.299μm, D50=0.482 μm, D90=1.036μm, and K90=(D90-D10) / D50=1.529.

[0046] S2. The precursor powder was calcined in a muffle furnace, heated to 500 °C for 6 h at a heating rate of 5 °C / min in air atmosphere, and then heated to 900 °C for 3 h at a heating rate of 5 °C / min to obtain the sodium-electric layered oxide precursor.

[0047] S3. Mix the precursor, LiCl, and LiNO3 at a mass ratio of 1:2:2. Place the mixture in a muffle furnace and calcine it at 400 °C for 2 hours in air at a heating rate of 5 °C / min. + / Na + Ion exchange treatment. After calcination, the material is added to deionized water and filtered. The filtered residue is then dried in an oven at 200 °C for 12 h to obtain O2-type lithium-rich manganese-based ternary cathode material.

[0048] Comparative Example 1 The only difference between this comparative example and Example 1 is that in step S1 of Comparative Example 1, the raw materials were mixed by manual grinding instead of ball milling, and the raw materials could not meet the submicron particle size requirements. Through particle size testing, the precursor raw materials at this time had D10=2.1 μm, D50=6.8 μm, D90=18.7 μm, and K90=(D90-D10) / D50=2.44. The remaining steps were the same as in Example 1, and lithium-rich manganese-based cathode materials were prepared.

[0049] Comparative Example 2 The only difference between this comparative example and Example 1 is that the sintering process in step S2 of comparative example 2 is a one-step sintering process, which involves heating to 900 ℃ for 9 h in air at a heating rate of 5 ℃ / min; the remaining steps are consistent with those in Example 1, and lithium-rich manganese-based cathode material is prepared.

[0050] The XRD pattern of the material prepared in this comparative example is as follows: Figure 3 As shown, characteristic diffraction peaks of the (020) superlattice belonging to the Li2MnO3 phase appeared in the range of 2θ=20°-25°.

[0051] Comparative Example 3 The only difference between this comparative example and Example 1 is that the sintering process in step S2 of comparative example 3 is a one-step sintering process, which is calcined at 800 ℃ for 9 h in air atmosphere at a heating rate of 5 ℃ / min; the remaining steps are the same as in Example 1, and lithium-rich manganese-based cathode material is prepared.

[0052] Comparative Example 4 The only difference between this comparative example and Example 1 is that the sintering process in step S2 of comparative example 4 is to calcine at 400°C for 6 h at a heating rate of 5°C / min in air atmosphere, and then calcine at 600°C for 3 h at a heating rate of 5°C / min; the remaining steps are the same as in Example 1, and lithium-rich manganese-based cathode material is prepared.

[0053] Comparative Example 5 The only difference between this comparative example and Example 1 is that in step S3 of Comparative Example 5, a single lithium salt, lithium nitrate, is used, and the mass ratio of the precursor to LiNO3 is 1:4; the remaining steps are consistent with those of Example 1, and lithium-rich manganese-based cathode material is prepared.

[0054] The XRD diffraction pattern of the lithium-rich manganese-based cathode material prepared in Comparative Example 5 is shown in Figure 5. Figure 4 Compared to multi-component lithium salt systems, single lithium salts are prone to problems such as unstable lithium source supply, uneven ion exchange reactions, and incomplete local reactions during high-temperature reactions. This leads to structural defects or impurities in the material and affects the formation and stability of the layered crystal structure. XRD images show that it is difficult to obtain O2-type layered oxide materials with uniform structure and high crystallinity using only a single lithium salt system.

[0055] Comparative Example 6 The only difference between this comparative example and Example 1 is that in step S3 of Comparative Example 6, the lithium salt ratio is precursor:LiCl:LiNO3=1:2:0.18, where the mass percentage of LiNO3 in the lithium salt is less than 10%; the remaining steps are the same as in Example 1, and lithium-rich manganese-based cathode material is prepared.

[0056] Comparative Example 7 The only difference between this comparative example and Example 1 is that in step S3 of Comparative Example 7, the ion exchange sintering temperature is 150°C and the holding time is 2h; the remaining steps are the same as in Example 1, and lithium-rich manganese-based cathode material is prepared.

[0057] Comparative Example 8 The only difference between this comparative example and Example 1 is that in step S3 of Comparative Example 8, the ion exchange sintering temperature is 550°C and the holding time is 2h; the remaining steps are the same as in Example 1, and lithium-rich manganese-based cathode material is prepared.

[0058] The electrochemical performance testing process for the lithium-rich manganese-based cathode materials prepared in the examples and comparative examples is as follows: The lithium-rich manganese-based cathode materials prepared in the examples and comparative examples were mixed with a conductive agent (C65) and a binder, polyvinylidene fluoride (PVDF), at a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added during mixing to prepare an electrode slurry. After uniform mixing using a high-speed mixer, the slurry was coated onto aluminum foil using a scraper and dried in an oven at 110°C for 8 hours. The electrode sheets were then cut into 14mm diameter discs. Related tests were conducted by assembling CR2032 coin cells. The coin cells used lithium metal as the negative electrode, PP-PE-PP (Celgard 825) as the separator, and the electrolyte composition was 1M LiPF6 with an EC / DMC volume ratio of 3:7. The entire battery assembly process was carried out in a glove box (O2 < 0.1 ppm, H2O < 0.1 ppm). After assembly, the batteries were allowed to stand for 8 hours, and then electrochemical performance tests were conducted within a voltage range of 2.0-4.8 V. The first charge-discharge test was performed at 0.1 C, and the long-cycle performance test was conducted at a rate of 1 C. The test results are shown below. Figure 5-11 And Table 1.

[0059] Table 1. Electrochemical performance data of the examples and comparative examples. The XRD diffraction patterns of the pure-phase O2-type lithium-rich manganese-based cathode materials prepared in Examples 1-5 show characteristic patterns that are different from those of traditional O2-type materials and materials obtained in the comparative examples. They present a single O2-type layered crystal structure without Li2MnO3 superlattice phase or other impurity phases, while the XRD patterns of comparative examples 1-8 show Li2MnO3 superlattice phase or impurity phase peaks of varying degrees.

[0060] And from Table 1 and Figure 5-11 It can be seen that the pure-phase O2-type lithium-rich manganese-based cathode materials prepared in Examples 1-5 of this invention all have a 0.1C discharge specific capacity exceeding 285 mAh·g⁻¹ and a capacity retention rate exceeding 89% after 30 cycles at 1C, demonstrating significantly better electrochemical performance than all comparative examples. Comparative Example 1 did not refine the raw materials to the submicron level, resulting in insufficient raw material reaction and non-uniform material composition, leading to a significant decrease in specific capacity and cycle stability. Comparative Examples 2 and 3 did not employ a two-step sintering process, resulting in the presence of impurity phases such as Li₂MnO₃ in the prepared precursors, significantly reducing the specific capacity and cycle retention rate of the final materials. Comparative Example 4 had an excessively low sintering temperature, resulting in poor crystallinity and numerous impurity phases in the cathode material, leading to abnormal first-efficiency performance and extremely poor cycle stability. Comparative Example 5 used a single lithium salt for ion exchange, failing to obtain a pure-phase O2-type structure, resulting in numerous structural defects and a significant decrease in electrochemical performance. In Comparative Example 6, the proportion of a single component in the multi-component lithium salt was less than 10%, failing to form a stable eutectic system, resulting in non-uniform ion exchange and a significant decrease in material performance. Comparative Example 7: Ion exchange temperature was too low, Li + / Na +The ion exchange reaction could not proceed fully, resulting in extremely low specific capacity and poor cycle stability of the material. In Comparative Example 8, the ion exchange temperature was too high, which damaged the O2 structure and reduced the electrochemical performance of the material.

[0061] The above results fully demonstrate that the present invention has successfully prepared a pure phase O2-type lithium-rich manganese-based cathode material without Li2MnO3 impurity phase through the synergistic effect of raw material particle size control, two-step sintering process and multi-component lithium salt ion exchange. The specific capacity and cycle stability of the battery prepared by this material are significantly improved, and it has excellent electrochemical performance.

[0062] Furthermore, comparing Examples 1 and 2 reveals that, compared to liquid-phase mixing (Example 2), the material obtained by solid-phase ball milling (Example 1) exhibits higher initial capacity and better cycle retention. Comparing Examples 1 and 3 shows that precise control of the precursor sintering temperature is crucial. Compared to 600℃ / 800℃ (Example 3), pre-sintering at 500℃ combined with high-temperature sintering at 900℃ (Example 1) can construct a more perfectly crystalline P2 phase precursor, thereby achieving superior electrochemical performance in the final cathode material. In multi-component lithium salt systems, the mixed system of lithium chloride and lithium nitrate (Example 1), compared to the combination of lithium bromide and lithium nitrate (Example 4), provides a more suitable eutectic liquid phase environment and ion exchange kinetics, which is more conducive to improving the overall electrochemical performance of the material.

[0063] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0064] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0065] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure, characterized in that, The positive electrode material has a chemical composition of Li. 1+x Mn y Ni z Co w O2, 0<x≤0.5, 0.3≤y≤0.7, 0.05≤z≤0.3, 0.05≤w≤0.4; The cathode material exhibits pure phase diffraction characteristics of a single O2-type layered structure, and its X-ray diffraction pattern does not show the (020) crystal plane characteristic diffraction peaks corresponding to the Li2MnO3 structure in the range of 2θ=20°-25°. The preparation method of the cathode material includes: mixing and pulverizing sodium source, nickel source, cobalt source and manganese source to refine to submicron level, and then performing two-step sintering to obtain P2 phase sodium-electric layered oxide precursor; A sodium-ion layered oxide precursor was mixed with a multi-component lithium salt and subjected to ion exchange treatment by sintering to obtain a lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure.

2. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, In the XRD pattern of the cathode material, the peak intensity ratio of the (002) crystal plane diffraction peak to the (104) crystal plane diffraction peak is I (002) / I (104) ≥5; And / or, based on the half-width at half-maximum (WHM) of the diffraction peaks of the (002) crystal plane and in conjunction with the Scherrer formula, the average grain size of the cathode material along the normal direction of the (002) crystal plane is 20~60 nm.

3. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, The sodium source is selected from inorganic compounds of sodium, including one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide; The nickel source is selected from inorganic compounds of nickel, including one or more of nickel oxide, nickel hydroxide, and nickel carbonate; The cobalt source is selected from inorganic compounds of cobalt, including one or more of cobalt oxide, cobalt hydroxide, and cobalt carbonate; The manganese source is selected from inorganic manganese compounds, including one or more of manganese dioxide, manganese oxide, and manganese carbonate.

4. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, The mixing and pulverizing process is carried out by ball milling at a speed of 100-500 rpm for 6-15 h. The ball milling process is solid-phase ball milling.

5. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, After the raw material is refined to the submicron level, the particle size distribution satisfies: D10<0.32μm, 0.35μm≤D50≤1.0μm, D90≤1.2μm, and the particle size distribution span K90=(D90-D10) / D50≥1.

2.

6. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, The two sintering steps are carried out in an air or oxygen atmosphere; The first step of pre-sintering is performed at a temperature of 500–650 °C for 5–8 h; the second step of sintering is performed at a temperature of 700–950 °C for 0.5–12 h; or, The first step of pre-sintering is carried out at a temperature of 500~580 ℃ for 5~7 h; the second step of sintering is carried out at a temperature of 850~930 ℃ for 2~5 h.

7. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, The multi-component lithium salt is a mixture of at least two of lithium hydroxide, lithium carbonate, lithium chloride, lithium nitrate, and lithium bromide; in the multi-component lithium salt, the mass percentage of any single-component lithium salt is ≥10%; or The multi-component lithium salt is a mixture of lithium chloride and lithium nitrate, with a mass ratio of lithium chloride to lithium nitrate of 1:0.8~1.

2.

8. The lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure according to claim 1, characterized in that, The atmosphere for sintering ion exchange treatment is selected from air, argon, or an argon-hydrogen mixture; the sintering temperature for sintering ion exchange treatment is 200~500 ℃, and the sintering time is 3~24 h.

9. A method for preparing a lithium-rich manganese-based cathode material with a pure-phase O2-type layered crystal structure as described in claim 1, characterized in that, Includes the following steps: (1) Sodium source, nickel source, cobalt source and manganese source are mixed and crushed to the submicron level, and then sintered in two steps to obtain P2 phase sodium-electric layered oxide precursor; (2) The sodium-ion layered oxide precursor is mixed with multi-component lithium salt and ion exchange is carried out by sintering to obtain lithium-rich manganese-based cathode material with pure phase O2 type layered crystal structure.

10. A lithium-ion battery cathode material, characterized in that, The material comprises a lithium-rich manganese-based cathode material having a pure-phase O2-type layered crystal structure as described in any one of claims 1-8, or a lithium-rich manganese-based cathode material having a pure-phase O2-type layered crystal structure obtained by the preparation method described in claim 9.

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