Modified lithium-rich manganese-based positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a modified lithium-rich manganese-based positive electrode material and a preparation method thereof and a lithium ion battery, and relates to the technical field of new energy sources.The modified lithium-rich manganese-based positive electrode material of the application strengthens the structure stability of the polycrystalline material by carrying out multi-element point doping on the base material, inhibits the migration of transition metal ions and the layer dislocation, improves the internal lattice strength, and manufactures a stable base material core; the heterogeneous structure layer can greatly improve the surface structure phase change and the transition metal dissolution of the material surface under high voltage, increase the stability of the base material surface, and the three-dimensional ion channel generated in situ can improve the rate performance of the material; the coating layer can effectively reduce the solid-liquid interface side reaction, improve the surface metal ion dissolution, and improve the cycle performance of the material; in summary, the application mainly modifies the internal structure and the surface of the material through three means of doping, interface structure design and coating, and can greatly improve the rate and long-term life of the material.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to a modified lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles, energy storage systems, and other fields, the demand for cathode materials with high energy density, long cycle life, and high safety is increasing. Lithium-rich manganese-based cathode materials have become a research hotspot in lithium-ion battery cathode materials due to their advantages such as high specific capacity (>250mAh / g), low cost, and environmental friendliness. Lithium-rich manganese-based cathode materials typically consist of a solid solution structure composed of layered Li₂MnO₃ and LiTMO₂ (TM = Ni, Co, Mn, etc.), exhibiting high theoretical capacity and operating voltage, but still facing many challenges in practical applications.

[0003] During charge and discharge, lithium-rich manganese-based cathode materials experience irreversible migration of transition metal ions due to the participation of anion redox reactions, leading to structural instability. Simultaneously, uneven lithium diffusion between the two phases causes stress accumulation, resulting in atomic-level interlayer dislocations and particle fracture, severely impacting the material's long-term cycle stability and safety performance. Furthermore, lithium-rich manganese-based materials also suffer from low initial coulombic efficiency and severe voltage decay, limiting their commercial application.

[0004] To address these issues, researchers have developed various modification strategies. However, existing modification methods still have some limitations. While liquid-phase modification is highly effective, its complex process hinders industrialization. Solid-phase modification, though low-cost and simple to control, suffers from poor diffusion of transition metal ions at the solid-solid interface, preventing complete and effective doping and leading to element accumulation on the material surface, thus affecting modification efficiency. Furthermore, current structural designs and element doping strategies for lithium-rich manganese-based materials have not fully resolved the structural stability issues during long-term cycling, particularly the irreversible phase transitions and capacity decay caused by anionic redox reactions.

[0005] Therefore, while ensuring performance, how to balance industrialization and effective modification to develop a lithium-rich manganese-based cathode material with stable structure, excellent cycle performance, and suitable for large-scale production is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The purpose of this application is to provide a modified lithium-rich manganese-based cathode material, its preparation method, and a lithium-ion battery, aiming to solve the problems of structural instability and cycle degradation of existing lithium-rich manganese-based cathode materials.

[0007] To achieve the above objectives, this application provides a modified lithium-rich manganese-based cathode material, comprising: a matrix material, a heterostructure layer, and a coating layer;

[0008] The matrix material is a polycrystalline or near-single-crystal solid solution particle with the chemical formula Li. w Ni x Mn y M a N b L c O w+1-r Q r Wherein, 1.2≤w≤1.4, 0.25≤x≤0.40, 0.50≤y≤0.70, 0.0005≤a≤0.002, 0.0001≤b≤0.002, 0.0001≤c≤0.004, x+y+a+b+c=1, 0≤r≤0.002;

[0009] Wherein, M and L are each independently selected from at least one of Nb, Ti, Mg, Co, W, La, Te, and Ta; preferably, M is selected from at least one of Nb, Ti, and Mg, and L is selected from at least one of Co, W, and La; more preferably, M and L are Nb and Co, respectively; N is selected from at least one of Zn, Na, Cr, Zr, and K; preferably, N is selected from at least one of Zn, Na, and K; more preferably, N is Zn; Q is selected from at least one of F, Cl, S, B, and P; preferably, Q is selected from at least one of F, Cl, S, and P.

[0010] The heterostructure layer contains spinel-phase lithium manganese oxide Li4Mn5O 12 ;

[0011] The coating layer is a D-containing compound, which includes one or more of Al and / or La fluorides, oxides, sulfates, nitrates or phosphates, preferably including one or more of Al fluorides, oxides, sulfates, nitrates or phosphates.

[0012] In some embodiments, the internal porosity of the modified lithium-rich manganese-based cathode material is ≥15%, preferably 15%~20%.

[0013] In some embodiments, the modified lithium-rich manganese-based cathode material has a secondary spherical morphology formed by primary particle stacking, and the average length of the primary particles is 150-200 nm.

[0014] In some embodiments, the average particle size D50 of the modified lithium-rich manganese-based cathode material is 3-10 μm.

[0015] This application also provides a method for preparing the above-mentioned modified lithium-rich manganese-based cathode material, comprising:

[0016] In an oxygen-containing atmosphere, Ni x Mn y (OH)2, lithium source, M-containing compound, N-containing compound and L-containing compound are mixed and sintered once to obtain a sintered product;

[0017] The first sintered product is subjected to a second sintering under an inert atmosphere to obtain a second sintered product with a heterogeneous structure layer.

[0018] The secondary sintering product is mixed with additives and sintered three times to obtain a modified lithium-rich manganese-based cathode material with a coating layer.

[0019] In some embodiments, at least one of the following conditions is met:

[0020] A. The Ni x Mn y In (OH)2, 0.28≤x≤0.42, 0.58≤y≤0.72, x+y=1;

[0021] B. The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, or lithium acetate;

[0022] C. The Ni x Mn y (OH)2: The molar ratio of the lithium source (the M-containing compound + the N-containing compound + the L-containing compound) is 0.997:(1.20~1.40):0.003;

[0023] D. The additives include at least one of aluminum fluoride, aluminum oxide, aluminum sulfate, aluminum nitrate, aluminum phosphate, lithium titanium aluminum phosphate, lanthanum oxide, and lithium aluminum zirconate;

[0024] Preferably, the additive includes at least one of alumina, aluminum fluoride, aluminum phosphate, and lanthanum oxide;

[0025] More preferably, the additive includes aluminum fluoride;

[0026] E. The amount of the additive added is 0.5%-1.5% of the mass of the dicalcined product.

[0027] In some embodiments, at least one of the following conditions is met:

[0028] A. The first sintering includes a first heat preservation platform, a second heat preservation platform, and a third heat preservation platform; the temperature of the first heat preservation platform is 300-450℃, the temperature of the second heat preservation platform is 450-650℃, and the temperature of the third heat preservation platform is 950-990℃;

[0029] B. Under condition A, the heating rate of the first insulation platform is 4~6℃ / min, and the heating rates of the second insulation platform and the third insulation platform are independently 1~3℃ / min.

[0030] C. Under condition A, the insulation time of the first insulation platform is 4-6 hours, the insulation time of the second insulation platform is 6-8 hours, and the insulation time of the third insulation platform is 10-12 hours.

[0031] In some embodiments, at least one of the following conditions is met:

[0032] A. The temperature of the secondary sintering is 400-600℃;

[0033] B. The heating rate for the secondary sintering is 3-5℃ / min;

[0034] C. The isothermal time for the secondary sintering is 5-10 hours;

[0035] D. The temperature for the three sintering processes is 400-500℃, the holding time is 4-6h, and the heating rate is 3-5℃ / min.

[0036] In some embodiments, at least one of the following conditions is met:

[0037] A. Sintering equipment includes one of the following: muffle furnace, tube furnace, chamber furnace, and bell furnace;

[0038] B. The oxygen-containing atmosphere includes one of pure oxygen, compressed air, purified gas, and ordinary air;

[0039] C. The Ni x Mn y The internal porosity of (OH)2 is ≥25%.

[0040] This application also provides a lithium-ion battery comprising the above-mentioned modified lithium-rich manganese-based cathode material.

[0041] Compared with the prior art, the beneficial effects of this application include:

[0042] The modified lithium-rich manganese-based cathode material provided in this application enhances the structural stability of the polycrystalline material by multi-element site doping of the matrix material, suppresses the migration of transition metal ions and interlayer dislocations, improves the internal lattice strength, and creates a stable matrix material core. The heterostructure layer can greatly improve the oxidation resistance of the material surface under high voltage, increase the stability of the matrix material surface, and the three-dimensional ion channels generated in situ can improve the rate performance of the material. The coating layer can effectively reduce the side reactions at the solid-liquid interface, improve the dissolution of surface metal ions, and improve the cycle performance of the material. In summary, this application mainly combines the above-mentioned specific element doping, heterostructure surface layer modification design, and surface coating to effectively and comprehensively modify the internal structure, surface layer, and outer surface of the material, thereby improving the capacity performance, rate performance, and cycle performance of the lithium-rich manganese-based cathode material.

[0043] The method for preparing the modified lithium-rich manganese-based cathode material provided in this application first utilizes a multi-stage heat preservation phase during a single sintering process to perform multi-site doping of specific elements on the matrix material, thereby improving its performance. Then, a high-temperature treatment is performed at 400-600℃ under an inert atmosphere, during which some oxygen on the material surface is oxidized, forming a certain amount of oxygen vacancies. Simultaneously, this reduces the migration energy of Mn ions, promoting Mn migration to the oxygen vacancies and generating in-situ lithium manganese oxide (Li4Mn5O) containing a spinel phase. 12 The material has a heterostructure layer; then it is coated with a D-containing compound to form a coating layer; by combining the above three methods of specific element doping, heterostructure surface layer modification design and surface coating, the internal structure, surface layer and outer surface of the material are effectively and comprehensively modified, and a synergistic effect is achieved, resulting in a modified lithium-rich manganese-based cathode material with improved capacity rate cycling performance.

[0044] If a single monoxide doping method is used, the internal structural strength of the crystal will increase to a certain extent, but the surface oxygen partial pressure will be too high and the oxygen activity will not be controlled. This will cause the material to be over-oxidized in a high-voltage environment, and the surface metal ions will continuously migrate into the interior, leading to structural decomposition. In addition, the lack of an effective coating layer on the surface to isolate the solid-liquid interface will also degrade the material's cycle performance. In summary, this application starts from the three levels of bulk, surface, and surface, and the comprehensive modification can greatly improve the electrochemical performance of the material, such as first-efficiency, cycle, and voltage decay. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0046] Figure 1 This is a schematic flowchart of the preparation method of the modified lithium-rich manganese-based cathode material of this application;

[0047] Figure 2 Here is a SEM image of the modified lithium-rich manganese-based cathode material from Example 1;

[0048] Figure 3 The XRD diffraction pattern of the modified lithium-rich manganese-based cathode material in Example 1 is shown below.

[0049] Figure 4 The XRD diffraction pattern of the modified lithium-rich manganese-based cathode material in Comparative Example 1 is shown.

[0050] Figure 5 The graph shows the cycle performance of the modified lithium-rich manganese-based cathode materials of Example 1 and Comparative Example 1. Detailed Implementation

[0051] As used in this article:

[0052] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0053] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0054] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0055] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0056] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0057] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0058] This application provides a modified lithium-rich manganese-based cathode material, comprising: a matrix material, a heterostructure layer, and a coating layer;

[0059] The matrix material is a polycrystalline or near-single-crystal solid solution particle with the chemical formula Li. w Ni x Mn y M a N b L c O w+1-r Q r Wherein, 1.2≤w≤1.4, 0.25≤x≤0.40, 0.50≤y≤0.70, 0.0005≤a≤0.002, 0.0001≤b≤0.002, 0.0001≤c≤0.004, x+y+a+b+c=1, 0≤r≤0.002;

[0060] Wherein, M and L are each independently selected from at least one of Nb, Ti, Mg, Co, W, La, Te and Ta, preferably, M is selected from at least one of Nb, Ti and Mg, and L is selected from at least one of Co, W and La, more preferably, M and L are Nb and Co respectively; N is selected from at least one of Zn, Na, Cr, Zr and K, preferably, N is selected from at least one of Zn, Na and K, more preferably, N is Zn; Q is selected from at least one of F, Cl, S, B and P, preferably, Q is selected from at least one of F, Cl, S and P; preferably, r is 0.

[0061] The heterostructure layer contains spinel-phase lithium manganese oxide Li4Mn5O 12 ;

[0062] The coating layer is a D-containing compound, which includes one or more of Al and / or La fluorides, oxides, sulfates, nitrates or phosphates, preferably including one or more of Al fluorides, oxides, sulfates, nitrates or phosphates.

[0063] The modified lithium-rich manganese-based cathode material provided in this application enhances the structural stability of the polycrystalline material by multi-element site doping of the matrix material, suppresses the migration of transition metal ions and interlayer dislocations, improves the internal lattice strength, and creates a stable matrix material core. The heterostructure layer can greatly enhance the oxidation resistance of the material surface under high voltage, increase the stability of the matrix material surface, and the three-dimensional ion channels generated in situ can improve the rate performance of the material. The coating layer can effectively reduce the side reactions at the solid-liquid interface, improve the dissolution of surface metal ions, and improve the cycle performance of the material. In summary, this application mainly combines the above-mentioned specific element doping, heterostructure surface layer modification design, and surface coating to effectively and comprehensively modify the internal structure, surface layer, and outer surface of the material, thereby improving the capacity performance, rate performance, and cycle performance of the lithium-rich manganese-based cathode material.

[0064] In some embodiments, M is preferably Nb, L is preferably Co, and N is preferably Zn.

[0065] The role of Nb in multi-element synergistic doping is twofold: first, it dops at the transition metal sites in the layered phase, enhancing the transition metal-oxygen bond energy, stabilizing transition metal ions in the crystal lattice, and reducing their migration barriers; second, excess Nb accumulates on the material surface and at grain boundaries, forming fast ion conductors such as LiNbO3 on the surface, improving the material's conductivity, and grain boundary enrichment inhibits primary particle growth, allowing the primary particles to maintain good crystallinity at high temperatures without losing capacity. Zn acts as a Li layer dopant, targeting Li vacancies and blocking the migration path of transition metal elements into the Li layer. Co enters the Li₂MnO₃ phase, catalyzing oxygen activity. This multi-element synergistic effect improves rate capability and discharge capacity.

[0066] Too low a Nb doping level will result in insufficient formation of transition metal-oxygen bonds or large-area grain boundary enrichment, failing to effectively prevent harmful phase transitions and structural degradation. Too high a doping level will lead to the formation or enrichment of inert metal impurities on the material surface, reducing the material's electrochemical activity and hindering lithium-ion extraction and insertion. Similarly, too low a Zn doping level will result in insufficient prevention of the migration of transition metal ions to the lithium layer, while too high a level will lead to increased cation mixing in the Li layer and excessively rapid structural collapse. Too low a Co doping level will fail to achieve a certain degree of O activation, while too high a doping level will lead to excessive O activation, accelerating structural decay.

[0067] In some embodiments, the internal porosity of the modified lithium-rich manganese-based cathode material is ≥15%, for example, it can be any value of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30% or ≥15%, preferably 15%~20%.

[0068] In some embodiments, the modified lithium-rich manganese-based cathode material has a secondary spherical morphology formed by primary particle stacking, wherein the average length of the primary particles is 150-200 nm, for example, it can be any value between 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or 150-200 nm.

[0069] In some embodiments, the average particle size D50 of the modified lithium-rich manganese-based cathode material is 3-10 μm, for example, it can be any value between 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or 3-10 μm.

[0070] This application also provides a method for preparing the above-mentioned modified lithium-rich manganese-based cathode material. Please refer to [link to relevant documentation]. Figure 1 ,include:

[0071] S100: In an oxygen-containing atmosphere, Ni x Mn y (OH)2, lithium source, M-containing compound, N-containing compound and L-containing compound are mixed and sintered once to obtain a sintered product;

[0072] S200: The first sintering product is sintered again under an inert atmosphere to obtain a second sintering product with a heterogeneous structure layer;

[0073] S300: The secondary sintering product is mixed with additives and sintered three times to obtain a modified lithium-rich manganese-based cathode material with a coating layer.

[0074] The method for preparing the modified lithium-rich manganese-based cathode material provided in this application first utilizes a multi-stage heat preservation phase during a single sintering process to perform multi-site doping of specific elements on the matrix material, thereby improving its performance. Then, it undergoes high-temperature treatment at 400-600℃ under an inert atmosphere (e.g., nitrogen, argon, or helium), during which some oxygen on the material surface is oxidized, forming a certain amount of oxygen vacancies. Simultaneously, this reduces the migration energy of Mn ions, promoting Mn migration to the oxygen vacancies and generating in-situ lithium manganese oxide (Li4Mn5O) containing a spinel phase. 12 The material has a heterostructure layer; then it is coated with a D-containing compound to form a coating layer; by combining the above three methods of specific element doping, heterostructure surface layer modification design and surface coating, the internal structure, surface layer and outer surface of the material are effectively and comprehensively modified, and a synergistic effect is achieved, resulting in a modified lithium-rich manganese-based cathode material with improved capacity rate cycling performance.

[0075] If a single monoxide doping method is used, the internal structural strength of the crystal will increase to a certain extent, but the surface oxygen partial pressure will be too high and the oxygen activity will not be controlled. This will cause the material to be over-oxidized in a high-voltage environment, and the surface metal ions will continuously migrate into the interior, leading to structural decomposition. In addition, the lack of an effective coating layer on the surface to isolate the solid-liquid interface will also degrade the material's cycle performance. In summary, this application starts from the three levels of bulk, surface, and surface, and the comprehensive modification can greatly improve the electrochemical performance of the material, such as first-efficiency, cycle, and voltage decay.

[0076] In some embodiments, Ni in step S100 x Mn y In (OH)2, 0.28≤x≤0.42, 0.58≤y≤0.72, x+y=1.

[0077] In some embodiments, the lithium source in step S100 includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, or lithium acetate.

[0078] In some embodiments, Ni in step S100 x Mn y The molar ratio of (OH)2:lithium source:(M-containing compound + N-containing compound + L-containing compound) is 0.997:(1.20~1.40):0.003, for example, it can be any ratio between 0.997:1.20:0.003, 0.997:1.25:0.003, 0.997:1.30:0.003, 0.997:1.35:0.003, 0.997:1.40:0.003 or 0.997:(1.20~1.40):0.003.

[0079] In some embodiments, the oxygen-containing atmosphere in step S100 includes one of pure oxygen, compressed air, purified gas, and ordinary air.

[0080] In some embodiments, Ni in step S100 x Mn y The internal porosity of (OH)2 is ≥25%.

[0081] In some embodiments, the first sintering in step S100 includes a first heat preservation platform, a second heat preservation platform, and a third heat preservation platform; the temperature of the first heat preservation platform is 300 - 450°C, for example, it can be 300°C, 350°C, 400°C, 450°C, or any value between 300 - 450°C, the temperature of the second heat preservation platform is 450 - 650°C, for example, it can be 450°C, 500°C, 550°C, 600°C, 650°C, or any value between 450 - 650°C, and the temperature of the third heat preservation platform is 950 - 990°C, for example, it can be 950°C, 960°C, 970°C, 980°C, 990°C, or any value between 950 - 990°C.

[0082] The first heat preservation platform mainly promotes the full reaction of the precursor and the lithium salt, mainly generating an intermediate transition phase Li w’ TM 1-w’ TM2O4 (0 < w’ < 1) and a layered phase LiTMO2. At this time, the M element gradually diffuses into the layered transition metal sites synchronously and randomly replaces the Ni / Mn atomic sites; the second heat preservation platform corresponds to the transformation of the LiTMO2 phase to the Li2MnO3 phase, and the L element gradually embeds into the Li2MnO3 lattice, replacing some Mn atoms to generate Li2[Li 1 / 3 [MnL] 2 / 3 O3; both the first heat preservation platform and the second heat preservation platform will be accompanied by the random replacement of the Li site by the N element; the third heat preservation platform is a high-temperature sintering, and the high temperature provides an ion diffusion driving force to promote the doping of each element in the corresponding lattice positions to complete the corresponding amount.

[0083] In some embodiments, the heating rate of the first heat preservation platform in step S100 is 4 - 6°C / min, for example, it can be 4°C / min, 5°C / min, 6°C / min, or any value between 4 - 6°C / min, and the heating rates of the second heat preservation platform and the third heat preservation platform are independently 1 - 3°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, or any value between 1 - 3°C / min.

[0084] In some embodiments, the heat preservation time of the first heat preservation platform in step S100 is 4 - 6h, for example, it can be 4h, 5h, 6h, or any value between 4 - 6h, the heat preservation time of the second heat preservation platform is 6 - 8h, for example, it can be 6h, 7h, 8h, or any value between 6 - 8h, and the heat preservation time of the third heat preservation platform is 10 - 12h, for example, it can be 10h, 11h, 12h, or any value between 10 - 12h.

[0085] In some embodiments, the secondary sintering temperature in step S200 is 400-600℃, for example, it can be any value between 400℃, 450℃, 500℃, 550℃, 600℃, or 400-600℃; the heating rate of the secondary sintering is 3-5℃ / min, for example, it can be any value between 3℃ / min, 4℃ / min, 5℃ / min, or 3-5℃ / min; the isothermal time of the secondary sintering is 5-10h, for example, it can be any value between 5h, 6h, 7h, 8h, 9h, 10h, or 5-10h. The thickness of the heterostructure layer can be appropriately controlled by the heat treatment temperature and time under an inert atmosphere, and can be controlled to be around a few nanometers. Too thick a layer will lead to a longer Li ion diffusion path and a reduced capacity, while too thin a layer will not have an obvious effect. The composition of the heterostructure layer can be detected by XRD diffraction pattern.

[0086] The product from the first sintering is sintered again under an inert atmosphere to generate a large number of oxygen vacancies, which react with surface metal elements to form a heterogeneous structure layer. This layer can greatly enhance the oxidation resistance of the material surface under high voltage, increase the stability of the matrix material surface, and the three-dimensional ion channels generated in situ can improve the rate performance of the material.

[0087] In some embodiments, the sintering equipment includes one of a muffle furnace, a tube furnace, a chamber furnace, and a bell furnace.

[0088] In some embodiments, the additive in step S300 includes at least one of aluminum fluoride, aluminum oxide, aluminum sulfate, aluminum nitrate, aluminum phosphate, lithium titanium aluminum phosphate, lanthanum oxide, and lithium aluminum zirconate.

[0089] Preferably, the additive includes at least one of alumina, aluminum fluoride, aluminum phosphate, and lanthanum oxide;

[0090] More preferably, the additive includes aluminum fluoride.

[0091] More preferably, the additive is aluminum fluoride. The role of aluminum fluoride is to reduce excessive side reactions at the solid-liquid interface by utilizing the high stability of fluorides in the electrolyte, thereby improving the cycle stability of the material, especially in lithium-rich high-voltage systems.

[0092] In some embodiments, the amount of additive added in step S300 is 0.5%-1.5% of the mass of the dicalcined product, for example, it can be any value between 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or 0.5%-1.5%.

[0093] Since step S300 is a dry coating process, it is impossible to achieve a uniform coating layer. Therefore, if the coating amount is too small, it will not be able to form a sufficient island-shaped coating network on the material surface, while if it is too large, it will lead to an increase in interface impedance and affect the discharge capacity.

[0094] In some embodiments, the temperature of the three sintering steps in step S300 is 400-500°C, for example, it can be any value between 400°C, 450°C, 500°C or 400-500°C; the isothermal time is 4-6h, for example, it can be any value between 4h, 5h, 6h or 4-6h; and the heating rate is 3-5°C / min, for example, it can be any value between 3°C / min, 4°C / min, 5°C / min or 3-5°C / min.

[0095] This application also provides a lithium-ion battery comprising the above-mentioned modified lithium-rich manganese-based cathode material.

[0096] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0097] Example 1

[0098] This embodiment provides a modified lithium-rich manganese-based cathode material, which comprises a matrix material, a heterostructure layer, and a coating layer. The matrix material is a polycrystalline solid solution particle with the chemical formula Li. w Ni x Mn y M a N b L c O w+1 , where w=1.33, x=0.349, y=0.648, M element is Nb, N element is Zn, L element is Co, a=0.001, b=0.0005, c=0.0015.

[0099] This embodiment also provides a method for preparing a modified lithium-rich manganese-based cathode material, comprising the following steps:

[0100] (1) In an oxygen-containing environment, Ni 0.35 Mn 0.65 (OH)₂ precursor, lithium carbonate, niobium oxide, cobalt hydroxyl oxide, and zinc oxide are mixed evenly, Ni x Mn yThe molar ratio of (OH)₂:lithium carbonate:(niobium oxide + cobalt hydroxyl oxide + zinc oxide) was 0.997:1.33:0.003, and sintering was carried out in a muffle furnace in a single sintering process. The single sintering process included three holding plateaus: the first holding plateau was at 350℃ with a heating rate of 5℃ / min and a holding time of 5 hours; the second holding plateau was at 550℃ with a heating rate of 2℃ / min and a holding time of 5 hours; and the third holding plateau was at 965℃ with a heating rate of 2℃ / min and a holding time of 7 hours. Ordinary air was used as the oxygen source during the sintering process, yielding Nb / Co / Zn doped products in the single sintering process.

[0101] (2) The obtained first sintered product was subjected to a second sintering treatment under a nitrogen atmosphere. The temperature was increased to 500℃ at 4℃ / min, held for 8 hours, and then cooled to room temperature to obtain a second sintered product with a heterogeneous structure layer.

[0102] (3) The obtained secondary calcination product is mixed evenly with the additive aluminum fluoride. The amount of additive added is 1% of the mass of the secondary calcination product. The third sintering is carried out. The temperature is raised to 450°C at 4°C / min, held for 5 hours, and then cooled to room temperature to obtain a lithium-rich manganese-based cathode material with a coating layer.

[0103] SEM image of the modified lithium-rich manganese-based cathode material prepared in Example 1 is shown below. Figure 2 As shown, the average particle size D50 is 6.5 μm, and the internal porosity is 18%; the XRD diffraction pattern of this modified lithium-rich manganese-based cathode material is shown in [reference needed]. Figure 3 The heterostructure layer contains spinel-phase lithium manganese oxide (Li4Mn5O). 12 The material exhibits a secondary spherical morphology formed by primary particle stacking, with the average length of the primary particles being 170 nm.

[0104] Example 2

[0105] The difference between Example 2 and Example 1 is that the temperature of the first heat preservation platform in step (1) of the preparation method of modified lithium-rich manganese-based cathode material is 300°C, the temperature of the second heat preservation platform is 450°C, and the temperature of the third heat preservation platform is 950°C. The remaining steps are the same as in Example 1.

[0106] Example 3

[0107] The difference between Example 3 and Example 1 is that the temperature of the first heat preservation platform in step (1) of the preparation method of modified lithium-rich manganese-based cathode material is 450°C, the temperature of the second heat preservation platform is 650°C, and the temperature of the third heat preservation platform is 990°C. The remaining steps are the same as in Example 1.

[0108] Example 4

[0109] The difference between Example 4 and Example 1 is that the Ni in step (1) of the preparation method of the modified lithium-rich manganese-based cathode material... 0.35 Mn 0.65 The molar ratio of (OH)2 precursor: lithium carbonate: (niobium oxide + cobalt hydroxyoxide + zinc oxide) is 0.997:1.20:0.003, and the remaining steps are the same as in Example 1.

[0110] Example 5

[0111] The difference between Example 5 and Example 1 is that in step (1) of the preparation method of the modified lithium-rich manganese-based cathode material, Ni 0.35 Mn 0.65 The molar ratio of (OH)2 precursor: lithium carbonate: (niobium oxide + cobalt hydroxyoxide + zinc oxide) is 0.997:1.40:0.003, and the remaining steps are the same as in Example 1.

[0112] Example 6

[0113] The difference between Example 6 and Example 1 is that M is Ti, N is Zn, and L is W, while the remaining steps are the same as in Example 1.

[0114] Comparative Example 1

[0115] The difference between Comparative Example 1 and Example 1 is that step (2) is omitted, while the remaining steps are the same as in Example 1.

[0116] The XRD diffraction pattern of the modified lithium-rich manganese-based cathode material in Comparative Example 1 is shown in [reference]. Figure 4 The presence of spinel phase lithium manganese oxide (Li4Mn5O) is not observed. 12 .

[0117] Comparative Example 2

[0118] The difference between Comparative Example 2 and Example 1 is that the temperature of the first heat preservation platform in step (1) of the preparation method of modified lithium-rich manganese-based cathode material is 260°C, the temperature of the second heat preservation platform is 400°C, and the temperature of the third heat preservation platform is 900°C. The remaining steps are the same as in Example 1.

[0119] Comparative Example 3

[0120] The difference between Comparative Example 3 and Example 1 is that the temperature of the first heat preservation platform in step (1) of the preparation method of modified lithium-rich manganese-based cathode material is 500°C, the temperature of the second heat preservation platform is 700°C, and the temperature of the third heat preservation platform is 1100°C. The remaining steps are the same as in Example 1.

[0121] Comparative Example 4

[0122] The difference between Comparative Example 4 and Example 1 is that the preparation method of modified lithium-rich manganese-based cathode material does not have a first heat preservation platform in step (1), the temperature of the second heat preservation platform is 550°C, the temperature of the third heat preservation platform is 965°C, and the remaining steps are the same as in Example 1.

[0123] Comparative Example 5

[0124] The difference between Comparative Example 5 and Example 1 is that in step (1) of the preparation method of modified lithium-rich manganese-based cathode material, cobalt hydroxyl oxide was not added for mixing, and the remaining steps were the same as in Example 1.

[0125] Test example:

[0126] Electrochemical performance testing

[0127] The positive electrode materials prepared in the examples and comparative examples were mixed with PVDF and NMP in a ratio of 90:5:5 to prepare a positive electrode slurry. This slurry was coated onto aluminum foil, dried, punched, and sheared to obtain the positive electrode sheet. The coin cells were assembled in a glove box. The positive electrode sheet was assembled with lithium foil, a separator, and electrolyte to form a coin cell. The assembled coin cell was placed in the mold of a hydraulic sealing machine, locked, pressure applied, and then unlocked to remove the sealed coin cell. The separator was a Celgard polypropylene membrane, and the electrolyte was purchased from Guangzhou Tinci.

[0128] The battery was tested using a Lanhe (model: CT3002A) battery test cabinet. The test voltage range was 2.5V to 4.52V. Specifically, the battery was charged at a constant current of 0.1C to 4.52V, charged at a constant voltage of 0.02C, and discharged at 0.1C to 2.5V, which was considered the first activation cycle. Then, the battery was charged at a constant current of 0.33C to 4.52V, charged at a constant voltage of 0.02C, and discharged at 1C to 2.5V. The discharge capacity after the second cycle was recorded as the 0.33C discharge capacity (mAh / g). Finally, the battery was charged at a constant current of 1C to 4.52V, charged at a constant voltage of 0.02C, and discharged at 1C to 2.5V. The discharge capacity after the second cycle was recorded as the 1C discharge capacity (mAh / g). This 1C charge-discharge cycle was repeated until the 80th cycle, and the discharge capacity at the 80th cycle was recorded. The 1C 80-cycle retention rate (%) was calculated.

[0129] The capacity retention rates of the modified lithium-rich manganese-based cathode materials in Example 1 and Comparative Example 1 are as follows: Figure 5 As shown in Table 1, the electrochemical performance test data of the cathode materials in each embodiment and comparative example are presented.

[0130] Table 1 Electrochemical performance test data of the cathode materials in each embodiment and comparative example

[0131]

[0132] Comparative Example 1, lacking a heterostructure layer, exhibited poor surface oxidation resistance, severe dissolution and rearrangement of transition metal ions, resulting in deteriorated cycle performance. Comparative Example 2, employing an excessively low sintering temperature, resulted in low material crystallinity, reduced lithium salt diffusion, phase reaction, and metal ion migration, leading to high internal resistance and consequently lower rate capacity and cycle life. Comparative Example 3, using an excessively high sintering temperature, resulted in excessively large primary particles, excessively long lithium ion migration paths, and reduced ionic conductivity, thus exhibiting even lower capacity and cycle life compared to Comparative Example 2 or Example 1. Comparative Example 4 lacked a first holding platform, leading to insufficient decomposition of lithium salt and precursors, and a relatively low proportion of layered and intermediate transition phases. This resulted in fewer doped metal ion sites during subsequent high-temperature solid-state reactions, reducing the impact on crystal structure stability and thus lowering cycle performance. Comparative Example 5, lacking Co doping, reduced lithium extraction at 3a / 3b sites, resulting in poorer capacity (rate capacity), but also improved cycle stability to some extent.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0134] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A modified lithium-rich manganese-based cathode material, characterized in that, include: Matrix material, heterogeneous structure layer and coating layer; The matrix material is a polycrystalline or near-single-crystal solid solution particle with the chemical formula Li. w Ni x Mn y M a N b L c O w+1 Where, 1.2≤w≤1.4, 0.25≤x≤0.40, 0.50≤y≤0.70, 0.0005≤a≤0.002, 0.0001≤b≤0.002, 0.0001≤c≤0.004, x+y+a+b+c=1; Wherein, M is selected from at least one of Nb and Ti; L is selected from at least one of Co and W; N is selected from Zn; The heterostructure layer contains spinel-phase lithium manganese oxide Li4Mn5O 12 ; The coating layer is a D-containing compound, which includes one or more of Al and / or La fluorides, oxides, sulfates or phosphates; The preparation method of the modified lithium-rich manganese-based cathode material includes: in an oxygen-containing atmosphere, Ni x Mn y (OH)2, lithium source, M-containing compound, N-containing compound and L-containing compound are mixed and sintered once to obtain a sintered product; The first sintered product is subjected to a second sintering under an inert atmosphere to obtain a second sintered product with a heterogeneous structure layer. The second sintering product is mixed with additives and sintered three times to obtain a modified lithium-rich manganese-based cathode material with a coating layer. The first sintering process includes a first heat preservation platform, a second heat preservation platform, and a third heat preservation platform; the temperature of the first heat preservation platform is 300-450℃, the temperature of the second heat preservation platform is 450-650℃, and the temperature of the third heat preservation platform is 950-990℃. The temperature for the secondary sintering is 400-600℃; The heating rate for the secondary sintering is 3-5℃ / min; The isothermal time for the secondary sintering is 5-10 hours; The temperature for the three sintering processes is 400-500℃, the holding time is 4-6h, and the heating rate is 3-5℃ / min.

2. The modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The modified lithium-rich manganese-based cathode material has an internal porosity of ≥15%.

3. The modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The modified lithium-rich manganese-based cathode material has a secondary spherical morphology formed by primary particle stacking, and the average length of the primary particles is 150-200 nm.

4. The modified lithium-rich manganese-based cathode material according to claim 1, characterized in that, The average particle size D50 of the modified lithium-rich manganese-based cathode material is 3-10 μm.

5. A method for preparing a modified lithium-rich manganese-based cathode material as described in any one of claims 1 to 4, characterized in that, include: In an oxygen-containing atmosphere, Ni x Mn y (OH)2, lithium source, M-containing compound, N-containing compound and L-containing compound are mixed and sintered once to obtain a sintered product; The first sintered product is subjected to a second sintering under an inert atmosphere to obtain a second sintered product with a heterogeneous structure layer. The second sintering product is mixed with additives and sintered three times to obtain a modified lithium-rich manganese-based cathode material with a coating layer. The first sintering includes a first heat preservation platform, a second heat preservation platform, and a third heat preservation platform; The temperature of the first insulation platform is 300-450℃, the temperature of the second insulation platform is 450-650℃, and the temperature of the third insulation platform is 950-990℃; The temperature for the secondary sintering is 400-600℃; The heating rate for the secondary sintering is 3-5℃ / min; The isothermal time for the secondary sintering is 5-10 hours; The temperature for the three sintering processes is 400-500℃, the holding time is 4-6h, and the heating rate is 3-5℃ / min.

6. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 5, characterized in that, At least one of the following conditions must be met: A. The Ni x Mn y In (OH)2, 0.28≤x≤0.42, 0.58≤y≤0.72, x+y=1; B. The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, or lithium acetate; C. The Ni x Mn y (OH)2: The molar ratio of the lithium source (the M-containing compound + the N-containing compound + the L-containing compound) is 0.997:(1.20~1.40):0.003; D. The additives include at least one of aluminum fluoride, aluminum oxide, aluminum sulfate, aluminum nitrate, aluminum phosphate, lithium titanium aluminum phosphate, lanthanum oxide, and lithium lanthanum aluminum zirconate; E. The amount of the additive added is 0.5%-1.5% of the mass of the dicalcined product.

7. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 5, characterized in that, At least one of the following conditions must be met: A. The heating rate of the first insulation platform is 4~6℃ / min, and the heating rates of the second insulation platform and the third insulation platform are independently 1~3℃ / min; B. The insulation time of the first insulation platform is 4-6 hours, the insulation time of the second insulation platform is 6-8 hours, and the insulation time of the third insulation platform is 10-12 hours.

8. The method for preparing the modified lithium-rich manganese-based cathode material according to claim 5, characterized in that, At least one of the following conditions must be met: A. Sintering equipment includes one of the following: muffle furnace, tube furnace, chamber furnace, and bell furnace; B. The oxygen-containing atmosphere includes one of pure oxygen, compressed air, and ordinary air; C. The Ni x Mn y The internal porosity of (OH)2 is ≥25%.

9. A lithium-ion battery, characterized in that, Including the modified lithium-rich manganese-based cathode material as described in any one of claims 1 to 4.

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