Lithium-rich positive electrode material and preparation method thereof, positive electrode plate, lithium ion battery and electric device

Abstract

The invention discloses a lithium-rich positive electrode material and a preparation method thereof, a positive electrode plate, a lithium ion battery and an electric device. The lithium-rich positive electrode material provided by the invention comprises an inner core and a flexible coating layer coating at least part of the surface of the inner core, the inner core comprises a lithium-rich material, and the flexible coating layer comprises an amorphous compound; and the flexible coating layer and the inner core form a mutual doping region. According to the lithium-rich positive electrode material provided by the invention, the flexible coating layer is formed on the surface of the inner core, and the amorphous compound in the flexible coating layer can be filled in surface pores of the lithium-rich material to form a mutual doping region, so that the contact region of the coating layer and the substrate is enlarged. Besides, elements in the coating layer can partially enter the matrix under proper conditions, element gradient is formed between the coating layer and the matrix, component mutation at an interface is reduced, the binding force is further improved, and the lithium-rich positive electrode material with high capacity and high cycle performance is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and relates to a lithium-rich positive electrode material, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0002] As the core energy storage unit of lithium ion batteries, lithium ion positive electrode materials have been widely used in key fields such as electric vehicles, 3C digital products and aerospace due to their controllable crystal structure, stable lithium deintercalation kinetics and good electrochemical compatibility. However, with the continuous upgrading of energy storage demand in downstream application scenarios, the performance short board of current lithium ion positive electrode materials has become increasingly prominent, which has been difficult to match the diversified demand of high capacity and high cycle performance of batteries in the market. These performance bottlenecks limit the application of lithium ion batteries. SUMMARY

[0003] Therefore, it is necessary to provide a lithium-rich positive electrode material with high capacity and high cycle performance, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device.

[0004] In some embodiments, a lithium-rich positive electrode material is provided, comprising a core and a flexible coating layer coated on at least part of the surface of the core; the core comprises a lithium-rich material, and the flexible coating layer comprises an amorphous compound.

[0005] The flexible coating layer and the core form a mutual doping region.

[0006] In some embodiments, the lithium-rich positive electrode material provided satisfies one or both of the following conditions:

[0007] (1) the amorphous compound contains at least any one of Ni, Co, Mn, Li, W, Mo, Nb, Ce, La, B and Si;

[0008] (2) the chemical formula of the lithium-rich material is Li 1.2-m Ni 0.8+m-q Mn q O2, wherein 0≤m≤0.2 and 0.5≤q≤1.

[0009] In some embodiments, the lithium-rich positive electrode material provided has a difference δBET between the specific surface area of the lithium-rich material before coating and the specific surface area of the lithium-rich positive electrode material of 0.02 m 2 / g ~ 1.0 m 2 / g.

[0010] In some embodiments, the lithium-rich positive electrode material provided satisfies one or more of the following conditions:

[0011] (1) the amorphous compound comprises at least one of Li3BO3, LiNbO3 and LiCoO2;

[0012] (2) the structure of the lithium-rich material is layered α-NaFeO2 structure, and in the characterization results of X-ray diffraction, 2θ is in the range of 20°-30°, and there is a Li2MnO3 characteristic superlattice diffraction peak;

[0013] (3) the D50 size of the lithium-rich material is 2.0 μm-10.0 μm;

[0014] (4) the lithium-rich material comprises secondary particles formed by aggregation of primary particles, and the average particle size of the primary particles is 50 nm-500 nm;

[0015] (5) the lithium-rich material comprises particles with spherical or spherical-like morphology.

[0016] In some embodiments, a preparation method of a lithium-rich positive electrode material is provided, comprising the following steps:

[0017] ball-milling the lithium-rich material and a coating agent, and then performing annealing treatment to form a flexible coating layer comprising an amorphous compound on at least part of the surface of the lithium-rich material, wherein the annealing temperature is not lower than the glass transition temperature of the amorphous compound.

[0018] In some embodiments, the preparation method provided satisfies one or more of the following conditions:

[0019] (1) the coating agent contains at least any one of Ni, Co, Mn, Li, W, Mo, Nb, Ce, La, B, Si;

[0020] (2) the coating agent comprises at least one of boric acid, metasilicic acid, cobalt hydroxide, niobium acid and tungsten acid;

[0021] (3) the mass ratio of the lithium-rich material to the coating agent is 1:(0.05%-2%);

[0022] (4) the ball-milling conditions include: ball-milling in air atmosphere, the ball-milling frequency is 20 Hz-50 Hz, and the ball-milling time is 5 h-10 h;

[0023] (5) the annealing temperature is 400-800℃, and the annealing time is 1-10 h;

[0024] (6) the annealing is performed in air atmosphere;

[0025] (7) the preparation method of the lithium-rich positive electrode material does not contain liquid phase substances and / or liquid phase reactions.

[0026] In some embodiments, the preparation method of the provided preparation method includes the following steps: mixing a lithium-rich material precursor and a lithium source, and performing a first calcination and a second calcination to prepare the lithium-rich material;

[0027] Optionally, the method for preparing the lithium-rich material satisfies one or more of the following conditions:

[0028] (1) The lithium source includes lithium carbonate, lithium hydroxide, lithium sulfate, lithium acetate or lithium oxalate;

[0029] (2) The chemical formula of the lithium-rich material precursor is Ni a Mn b Co c (OH)₂, where 0 ≤ a ≤ 0.5, 0.5 ≤ b ≤ 1, 0 ≤ c ≤ 0.3;

[0030] (3) The molar ratio of the lithium-rich material precursor to the lithium source is 1:1.04~1.56;

[0031] (4) The conditions for the first calcination include: a temperature of 400~600℃, and / or a heating rate of 1.0℃ / min~5.0℃ / min, and / or a time of 1h~10h, and / or an environment of air or oxygen atmosphere;

[0032] (5) The conditions for the second calcination include: a temperature of 600~1000℃, and / or a heating rate of 1.0℃ / min~5.0℃ / min, and / or a time of 6~20h, and / or an environment of air or oxygen atmosphere.

[0033] In some embodiments, a positive electrode sheet is provided, comprising the lithium-rich positive electrode material or the lithium-rich positive electrode material prepared by the preparation method described above.

[0034] In some embodiments, a lithium-ion battery is provided, including the aforementioned positive electrode.

[0035] In some embodiments, an electrical device is provided, including the aforementioned lithium-ion battery.

[0036] The provided lithium-rich cathode material forms a flexible coating layer on the surface of the core. Amorphous compounds in this flexible coating layer can fill the pores on the surface of the lithium-rich material, forming inter-doped regions and increasing the contact area between the coating layer and the substrate. Furthermore, elements in the coating layer can partially enter the substrate under suitable conditions, forming an elemental gradient between the coating layer and the substrate, reducing abrupt compositional changes at the interface, further enhancing the bonding strength, and resulting in a high-capacity, high-cycle-performance lithium-rich cathode material. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments and examples of this application, and to more completely understand this application and its beneficial effects, the accompanying drawings used in the description of the embodiments or examples will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0038] Figure 1 The results are obtained by scanning electron microscopy of the lithium-rich cathode material prepared in Example 1. Detailed Implementation

[0039] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0040] It should be noted that when a component is said to be "fixed to" another component, it can be directly attached to the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0043] The terms "and / or," "or / and," and "and / or" as used in this application encompass any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR." For example, "A and / or B" includes three parallel solutions: A, B, and "a combination of A and B."

[0044] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0045] The terms “combinations thereof,” “any combination thereof,” and “any combination thereof” as used in this application include all suitable combinations of any two or more of the listed items.

[0046] In this application, the term "suitable" as used in "suitable combination", "suitable method", "any suitable method", etc., refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0047] In this application, terms such as "preferred," "better," "more suitable," and "ideal" are merely used to describe implementation methods or embodiments that achieve better results, and should be understood not to limit the scope of protection of this application.

[0048] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0049] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0050] In this invention, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0051] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0052] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0053] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0054] In this application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass-volume percentage.

[0055] In this application, "room temperature" generally refers to 5℃~30℃, and more preferably 25±5℃.

[0056] In this paper, the term "lithium-rich materials" refers to a class of materials whose chemical formula has a molar ratio of (lithium / all transition metals) greater than 1.

[0057] In this paper, the term "amorphous compound" refers to "amorphous materials," also known as "non-crystalline materials," which are a class of materials whose microstructure exhibits short-range order only within small intervals. Due to long-range disorder, compared to crystals, these materials often do not have a fixed melting point, and X-ray diffraction characterization methods cannot obtain diffraction peaks or can only obtain broadened diffraction peak regions.

[0058] In this document, δBET specifically refers to the difference between the specific surface area of ​​the lithium-rich material before coating and the specific surface area of ​​the lithium-rich material after coating.

[0059] In this document, other terms such as “doping” and “calcination” have the general meanings understood by those skilled in the art, unless otherwise stated.

[0060] In this paper, "inter-doped region" refers to the doped region formed by the diffusion of elemental components or phase structures between the coating layer and the matrix near the interface.

[0061] Lithium-rich materials possess high capacity, but their application is currently limited by major issues such as poor reversibility and easy gas generation due to their unique anionic redox reactions. Current surface protection methods include gas-phase or liquid-phase pre-deoxidation and surface coating modification. Gas-phase and liquid-phase treatments are difficult to scale up production, and the generated waste gas and wastewater require additional harmless treatment, resulting in high costs. Solid-phase surface coating is limited by the crystal structure of the coating layer and the substrate; semi-coherent and incoherent coating layers have low adhesion to the substrate.

[0062] In some embodiments, a lithium-rich cathode material is provided, comprising a core and a flexible coating layer covering at least a portion of the surface of the core; the core comprises a lithium-rich material, and the flexible coating layer comprises an amorphous compound.

[0063] The flexible coating layer and the core form an inter-doped region.

[0064] In the provided lithium-rich cathode material, the elements in the flexible coating layer are doped into the shallow lithium-rich cathode material.

[0065] Coating the surface of lithium-rich materials with flexible amorphous compounds can provide physical isolation between the lithium-rich materials and the electrolyte. At the same time, the flexible coating layer can fill surface pores, reduce the specific surface area of ​​the material, suppress side reactions, and improve cycle performance and storage performance.

[0066] The provided lithium-rich cathode material exhibits high stability under high voltage, low gas production, and high cycle retention rate.

[0067] In some embodiments, the amorphous compound in the flexible coating is uniformly distributed on the surface of the lithium-rich material.

[0068] In some embodiments, the provided lithium-rich cathode material contains at least one element selected from Ni, Co, Mn, Li, W, Mo, Nb, Ce, La, B, and Si in its amorphous compound.

[0069] In some embodiments, the provided lithium-rich cathode material has the chemical formula Li. 1.2-m Ni 0.8+m- q Mn q O2, where 0≤m≤0.2, 0.5≤q≤1, for example, m can be 0, 0.1, 0.2, etc., or a range of any two of the aforementioned values; q can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., or a range of any two of the aforementioned values.

[0070] In some embodiments, the difference δBET between the specific surface area of ​​the uncoated lithium-rich cathode material and the specific surface area of ​​the lithium-rich cathode material is 0.02 m². 2 / g ~1.0m 2 / g, for example, the difference δBET between the specific surface area of ​​the uncoated lithium-rich material and the specific surface area of ​​the lithium-rich cathode material can be 0.02 m 2 / g, 0.05m 2 / g, 0.1m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1 m 2 / g, etc., can also be a range composed of any two of the aforementioned values. Specific surface area (BET) can affect the active sites on the material surface. Controlling the specific surface area within this range can balance the capacity utilization and cycle performance of lithium-rich cathode materials.

[0071] In some embodiments, the amorphous compound in the provided lithium-rich cathode material comprises at least one of Li3BO3, LiNbO3, and LiCoO2.

[0072] In some embodiments, the lithium-rich cathode material provided has a layered α-NaFeO2 structure, and in the X-ray diffraction characterization results, 2ɵ has a Li2MnO3 characteristic superlattice diffraction peak in the range of 20°~30°.

[0073] In some embodiments, the D50 size of the provided lithium-rich cathode material is 2.0 μm to 10.0 μm. For example, the D50 size of the lithium-rich material can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc., or it can be any combination of two of the aforementioned values. A larger D50 is beneficial for increasing the material's compaction density and volumetric energy density, but an excessively large D50 is detrimental to capacity utilization. A smaller D50 is beneficial for capacity utilization but detrimental to compaction density. Controlling the D50 size of the lithium-rich material within this range, and combining lithium-rich materials with different D50 sizes, helps to balance the compaction density, volumetric energy density, and capacity utilization performance of the lithium-rich cathode material.

[0074] In some embodiments, the provided lithium-rich cathode material includes secondary particles formed by the aggregation of primary particles. The average particle size of the primary particles is 50 nm to 500 nm. For example, the average particle size of the primary particles can be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc., or any combination of the aforementioned values. Smaller primary particles are beneficial for capacity utilization but detrimental to material cycle performance, while larger primary particles have the opposite effect. Controlling the particle size of the primary particles within this range is beneficial for balancing the long-term performance and short-term capacity utilization of the lithium-rich cathode material.

[0075] In some embodiments, the provided lithium-rich cathode material includes particles having a spherical or near-spherical morphology.

[0076] In some embodiments, a method for preparing a lithium-rich cathode material is provided, comprising the following steps:

[0077] The lithium-rich material and the coating agent are ball-milled and then annealed to form a flexible coating layer containing an amorphous compound on at least a portion of the surface of the lithium-rich material, wherein the annealing temperature is not lower than the glass transition temperature of the amorphous compound.

[0078] In the provided method for preparing lithium-rich cathode materials, the ball milling process not only ensures thorough mixing of the raw materials but also provides initial driving force for the reaction, enhancing the reactivity of the raw materials and promoting their interpenetration and reaction. During annealing, elements in the flexible coating layer can enter the lithium-rich material lattice, forming doping in the shallow surface region and creating an elemental gradient between the flexible coating layer and the lithium-rich material, further promoting close contact between the coating layer and the lithium-rich material. Through ball milling and annealing, the coating agent reacts with residual lithium on the surface of the lithium-rich material to generate amorphous compounds. Above the glass transition temperature, amorphous compounds are typically flexible, allowing for good contact with the surface of the lithium-rich material, filling the surface pores and protecting the lithium-rich material from electrolyte corrosion. The amorphous compounds contain elements that easily enter the lithium-rich material lattice, enabling some coating elements to enter the lithium-rich material matrix during annealing, forming an elemental gradient between the matrix and the coating layer, reducing the tendency to peel off, and further increasing the coating effect.

[0079] The provided method for preparing lithium-rich cathode materials allows for the uniform coverage of the flexible coating layer on the surface of the lithium-rich material, avoiding issues such as island-like coating and coating layer peeling. Furthermore, the uniform coating layer reduces the specific surface area of ​​the material, suppresses interfacial side reactions and gas generation, and improves the cycle performance of the lithium-rich material.

[0080] In some embodiments, the coating agent in the provided preparation method contains at least one element selected from Ni, Co, Mn, Li, W, Mo, Nb, Ce, La, B, and Si.

[0081] In some embodiments, the coating agent in the provided preparation method includes at least one selected from boric acid, metasilicic acid, cobalt hydroxide, niobic acid, and tungstic acid.

[0082] In some embodiments, the mass ratio of lithium-rich material to coating agent in the provided preparation method is 1:(0.05%-2%). For example, the mass ratio of lithium-rich material to coating agent can be 1:0.05%, 1:0.1%, 1:0.5%, 1:1%, 1:15%, 1:2%, etc., or it can be a range of any two of the aforementioned ratios. By using a coating agent to modify the surface of the lithium-rich material and controlling the mass ratio of lithium-rich material to coating agent within this range, the capacity of the prepared lithium-rich cathode material will not deteriorate, ensuring its effective performance. In some embodiments, the ball milling conditions in the provided preparation method include: ball milling in an air atmosphere, a ball milling frequency of 20 Hz to 50 Hz, and a ball milling time of 5 h to 10 h. For example, the ball milling frequency can be 20 Hz, 30 Hz, 40 Hz, 50 Hz, or any combination of the aforementioned values. The ball milling time can be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any combination of the aforementioned values. The ball milling frequency and time determine the material mixing and coating effect. Controlling the ball milling frequency and time within this range allows for thorough mixing of the lithium-rich material and the coating agent while avoiding damage to the spherical morphology of the material, thus achieving a balance between material protection and mixing effects.

[0083] In some embodiments, the annealing temperature in the provided preparation method is 400℃~800℃, and the annealing time is 1h~10h. For example, the annealing temperature can be 400℃, 500℃, 600℃, 700℃, 800℃, etc., or any combination of the aforementioned values. The annealing time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc., or any combination of the aforementioned values. Controlling the annealing temperature within this range helps to improve the coating effect and the formation of the coating layer, while also controlling the diffusion of elements in the material, thereby improving the capacity utilization and cycle performance of the lithium-rich cathode material.

[0084] In some embodiments, the preparation method is provided in which annealing is performed in an air atmosphere.

[0085] In some embodiments, the preparation method of the lithium-rich cathode material does not involve liquid phase substances and / or liquid phase reactions.

[0086] In some embodiments, the preparation method of the provided preparation method includes the following steps: mixing a lithium-rich material precursor and a lithium source, and performing a first calcination and a second calcination to prepare the lithium-rich material.

[0087] In some embodiments, the lithium source in the preparation method of lithium-rich materials includes lithium carbonate, lithium hydroxide, lithium sulfate, lithium acetate, or lithium oxalate.

[0088] In some embodiments, the chemical formula of the lithium-rich material precursor is Ni in the preparation method of the lithium-rich material. a Mn b Co c (OH)₂, where 0≤a≤0.5, 0.5≤b≤1, 0≤c≤0.3. For example, a can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range of any two of the aforementioned values. For example, b can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., or a range of any two of the aforementioned values. For example, c can be 0, 0.1, 0.2, 0.3, etc., or a range of any two of the aforementioned values.

[0089] In some embodiments, the molar ratio of the lithium-rich material precursor to the lithium source in the preparation method of the lithium-rich material is 1:1.04 to 1.56. For example, the molar ratio of the lithium-rich material precursor to the lithium source can be 1:1.04, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.56, etc., or any range of two of the aforementioned ratios. The lithium ratio affects the capacity utilization and performance of the material. Controlling the molar ratio of the lithium-rich material precursor to the lithium source within this range helps to improve the capacity utilization and cycle performance of the lithium-rich cathode material.

[0090] In some embodiments, the conditions for the first calcination in the preparation method of lithium-rich materials include: a temperature of 400~600℃, and / or a heating rate of 1.0℃ / min~5.0℃ / min, and / or a time of 1h~10h, and / or an environment of air or oxygen atmosphere. For example, the temperature can be 400℃, 500℃, 600℃, etc., or it can be a range of any two of the aforementioned values. The heating rate can be 1.0℃ / min, 2.0℃ / min, 3.0℃ / min, 4.0℃ / min, 5.0℃ / min, etc., or it can be any combination of two of the aforementioned values. For example, the time can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc., or it can be any combination of two of the aforementioned values. The sintering method affects the phase formation and lattice perfection of the material. Longer sintering time will make the reaction more complete, but too long a time will lead to excessive lithium volatilization. Controlling the sintering time within this range is beneficial to the capacity utilization and cycle performance of lithium-rich cathode materials.

[0091] In some embodiments, the conditions for the second calcination in the method for preparing lithium-rich materials include: a temperature of 600~1000℃, and / or a heating rate of 1.0℃ / min~5.0℃ / min, and / or a time of 6~20h, and / or an environment of air or oxygen atmosphere. For example, the temperature can be 600℃, 700℃, 800℃, etc., or any combination of the aforementioned two values; the heating rate can be 1.0℃ / min, 2.0℃ / min, 3.0℃ / min, 4.0℃ / min, 5.0℃ / min, etc., or any combination of the aforementioned two values. For example, the time can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, etc., or any combination of the aforementioned two values. Controlling the second calcination temperature within this range helps in the formation of the material's phase and crystal structure, avoids excessive lithium volatilization, and facilitates the synthesis, capacity utilization, and cycle performance of lithium-rich cathode materials. In some embodiments, a cathode sheet is provided, comprising a lithium-rich cathode material or a lithium-rich cathode material prepared by a preparation method.

[0092] In some embodiments, a lithium-ion battery is provided, including a positive electrode.

[0093] In some embodiments, an electrical device is provided, including a lithium-ion battery. The following are specific embodiments. This is intended to provide further detailed description of the present application to help those skilled in the art and researchers to further understand it. The technical conditions, etc., do not constitute any limitation on the present application. Any modifications made within the scope of the claims of this application are within the protection scope of the claims of this application.

[0094] Unless otherwise stated, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods. Experimental methods not specifying particular conditions in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0095] Example 1

[0096] This embodiment provides a lithium-rich cathode material, comprising a lithium-rich material core and a flexible coating layer covering the lithium-rich material. The mass ratio of the flexible coating layer to the lithium-rich material is 2000 ppm:1. The preparation method is as follows:

[0097] S1. Weigh 1000g of lithium-rich material precursor, whose chemical formula is Ni. 0.35 Mn 0.65(OH)2, weigh 593g of lithium carbonate as the lithium source; mix the above materials evenly with a high-speed mixer, load into a sagger, and calcine in a box furnace. Calcination is divided into two steps: the first step uses 500℃ for 6 hours, and the second step uses 900℃ for 15 hours. Subsequently, the sintered material is pulverized and passed through a 325-mesh sieve to obtain primary sinter A;

[0098] S2. Weigh out the primary sinter A and the coating agent cobalt hydroxide (chemical formula Co(OH)2) according to the specified ratio. Ball mill the mixture in air at 25 Hz for 5 hours. Then anneal in air at 750℃ for 8 hours. Cool the sinter in the furnace, pulverize it, and pass it through a 325-mesh sieve to obtain the LiCoO2-coated lithium-rich cathode material Li. 1.16 Ni 0.294 Mn 0.546 O2.

[0099] Example 2

[0100] This embodiment provides a lithium-rich cathode material, comprising a lithium-rich material core and a flexible coating layer covering the lithium-rich material. The mass ratio of the flexible coating layer to the lithium-rich material is 4000 ppm:1. The preparation method is as follows:

[0101] The preparation method of this lithium-rich cathode material differs from that in Example 1 in that: the coating agent used is metasilicic acid (chemical formula H2SiO3), and the annealing temperature is changed to 500℃, resulting in a Li2SiO3-coated lithium-rich cathode material Li... 1.16 Ni 0.294 Mn 0.546 O2.

[0102] Example 3

[0103] This embodiment provides a lithium-rich cathode material, comprising a lithium-rich material core and a flexible coating layer covering the lithium-rich material. The mass ratio of the flexible coating layer to the lithium-rich material is 10000 ppm:1. The preparation method is as follows:

[0104] The preparation method of this lithium-rich cathode material differs from that in Example 1 in that the coating agent used is boric acid (chemical formula H3BO3), and the annealing temperature is changed to 600℃, resulting in a Li3BO3-coated lithium-rich cathode material. 1.16 Ni 0.294 Mn 0.546 O2.

[0105] Comparative Example 1

[0106] This comparative example provides a lithium-rich cathode material, and the specific implementation scheme is as follows:

[0107] The preparation method of this lithium-rich cathode material differs from that in Example 1 in that: no coating agent is used, and the material is directly annealed to obtain the lithium-rich cathode material Li. 1.16 Ni 0.294 Mn 0.546 O2.

[0108] Comparative Example 2

[0109] This comparative example provides a lithium-rich cathode material, comprising a lithium-rich material core and a shell covering it, wherein the mass ratio of the shell to the lithium-rich material is 2000 ppm. The preparation method is as follows:

[0110] The preparation method of this lithium-rich cathode material differs from that in Example 1 in that the coating agent used is zirconium oxide (chemical formula ZrO2), resulting in a ZrO2-coated lithium-rich cathode material, Li. 1.16 Ni 0.294 Mn 0.546 O2.

[0111] Comparative Example 3

[0112] This comparative example provides a lithium-rich cathode material, comprising a lithium-rich material core and a shell covering it, the shell having a mass fraction of 10000 ppm. The preparation method is as follows:

[0113] The preparation method of this lithium-rich cathode material differs from that of Example 3 in that the coating annealing temperature is 150℃, resulting in the H3BO3-coated lithium-rich cathode material Li. 1.16 Ni 0.294 Mn 0.546 O2.

[0114] The prepared lithium-rich cathode material was characterized using scanning electron microscopy (SEM). The results for the powder sample in Example 1 are as follows: Figure 1 As shown. From Figure 1 As can be seen, the sample consists of secondary spherical particles formed by the aggregation of multiple primary particles. The overall morphology is uniform, the secondary particles are intact, and there is no adhesion. There is no obvious coating agent residue or precipitation, indicating that the coating effect is good.

[0115] The composition of the lithium-rich materials prepared in each embodiment and comparative example was determined using an ICP-OES (inductively coupled plasma atomic emission spectrometer).

[0116] The specific surface area (BET) of the lithium-rich materials (i.e., sintered material A) and lithium-rich cathode materials prepared in each embodiment and comparative example was measured using a specific surface area analyzer, and the difference δBET was calculated, where δBET = specific surface area of ​​lithium-rich material - specific surface area of ​​lithium-rich cathode material. The results are shown in Table 1.

[0117] Table 1

[0118]

[0119] When a coating agent that does not react or forms a poor coating layer is used, the BET of the prepared lithium-rich cathode material will increase because the BET of the coating agent itself is higher than that of the lithium-rich material. Only when a uniform and continuous coating layer is formed, effectively filling the surface pores, will the BET decrease after coating. As shown in Table 1, the specific surface area of ​​the lithium-rich cathode materials prepared in Examples 1-3 is 0.322 m² lower than that of the uncoated lithium-rich material. 2 / g~0.732m 2 / g indicates that the lithium-rich cathode material provided in the examples forms a uniform and continuous coating layer. The amorphous compounds in the coating layer effectively fill the surface pores of the lithium-rich material, forming a co-doped region. In Comparative Example 3, the coating annealing temperature is lower than the glass transition temperature of the coating layer, resulting in a significant reduction in the specific surface area of ​​the lithium-rich cathode material.

[0120] Assemble the lithium-rich cathode materials prepared in the above embodiments and comparative examples into a battery, specifically including:

[0121] The specific preparation process is as follows: The positive electrode material, acetylene black conductive agent, and polyvinylidene fluoride binder are mixed evenly in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone is added as a dispersant and the mixture is homogenized. The resulting slurry is then uniformly coated onto a copper foil, vacuum dried at 120°C for 12 hours, and then cut into round pieces as positive electrode sheets with an active material loading of 10 mg / cm2.

[0122] A coin cell was assembled in a glove box under an argon atmosphere (oxygen content ≤ 0.1 ppm, water content ≤ 0.1 ppm); the above positive electrode, negative lithium metal sheet, and lithium hexafluorophosphate electrolyte (dissolved in a 1:1 volume ratio of ethylene carbonate and dimethyl carbonate) were assembled into a CR2032 type coin cell to obtain a coin cell for testing.

[0123] The electrochemical performance of the batteries prepared above was tested using the following methods:

[0124] Discharge specific capacity test: Test conditions are 0.1C, 2.3V~4.6V.

[0125] Cycle retention test: Test conditions are 0.33C, 2.3V~4.6V.

[0126] The test results are shown in Table 2.

[0127] Table 2

[0128]

[0129] As can be seen from Tables 1 and 2:

[0130] Compared with Comparative Example 1, Examples 1-3 show that the flexible coating layer used in this application can effectively reduce BET, suppress interfacial side reactions, and thus improve cycle stability.

[0131] Compared with Comparative Example 3, Example 3 shows that the coating annealing temperature in Comparative Example 3 is lower than the glass transition temperature of the coating layer, resulting in a significant reduction in the specific surface area of ​​the lithium-rich cathode material, excessive clogging of material pores, loss of surface active sites, and reduced material electrical performance. This application, by adjusting the annealing temperature, can promote the formation of a flexible coating layer, facilitate the diffusion of coating elements into the core to form an elemental gradient, increase the integrity of the coating layer, inhibit coating layer peeling, and alleviate the erosion of the lithium-rich material by the electrolyte during cycling.

[0132] Compared with Comparative Example 2, Examples 1-3 show that this application, by adjusting the types of coating elements and selecting elements that easily form flexible coating layers, forms a uniform and complete coating layer under appropriate conditions. This reduces BET (Burden-Effect Transmission), allows elements to diffuse in the bulk phase of lithium-rich materials, and creates an elemental gradient between the substrate and the coating layer, acting as a buffer. Surface damage during cycling is mainly due to side reactions at the interface between the electrolyte and the cathode material. Reducing BET decreases the reactive surface area, and the formed coating layer provides physical isolation for the cathode material. The lithium-conducting coating layer also suppresses impedance rise, promotes lithium-ion kinetics, improves cycle stability and storage performance, and suppresses gas generation. The cathode material of this application features low gas generation, high lithium-ion kinetics, and high cycle retention.

[0133] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A lithium-rich cathode material, characterized in that, The device comprises a core and a flexible coating layer covering at least a portion of the surface of the core; the core comprises a lithium-rich material and the flexible coating layer comprises an amorphous compound. The flexible coating layer forms an inter-doped region with the core.

2. The lithium-rich cathode material according to claim 1, characterized in that, One or both of the following conditions must be met: (1) The amorphous compound contains at least one element selected from Ni, Co, Mn, Li, W, Mo, Nb, Ce, La, B, and Si; (2) The chemical formula of the lithium-rich material is Li 1.2-m Ni 0.8+m-q Mn q O2, where 0≤m≤0.2, 0.5≤q≤1.

3. The lithium-rich cathode material according to claim 1, characterized in that, The difference δBET between the specific surface area of ​​the uncoated lithium-rich material and the specific surface area of ​​the lithium-rich cathode material is 0.02 m². 2 / g ~1.0m 2 / g.

4. The lithium-rich cathode material according to any one of claims 1 to 3, characterized in that, One or more of the following conditions must be met: (1) The amorphous compound comprises at least one of Li3BO3, LiNbO3 and LiCoO2; (2) The structure of the lithium-rich material is a layered α-NaFeO2 structure, and in the characterization results of X-ray diffraction, 2ɵ has the characteristic superlattice diffraction peak of Li2MnO3 in the range of 20°~30°. (3) The D50 size of the lithium-rich material is 2.0 μm to 10.0 μm; (4) The lithium-rich material includes secondary particles formed by the aggregation of primary particles, wherein the average particle size of the primary particles is 50 nm to 500 nm. (5) The lithium-rich material includes particles with a spherical or near-spherical morphology.

5. The method for preparing the lithium-rich cathode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: The lithium-rich material and the coating agent are ball-milled and then annealed to form a flexible coating layer containing an amorphous compound on at least a portion of the surface of the lithium-rich material, wherein the annealing temperature is not lower than the glass transition temperature of the amorphous compound.

6. The preparation method according to claim 5, characterized in that, One or more of the following conditions must be met: (1) The coating agent contains at least one element selected from Ni, Co, Mn, Li, W, Mo, Nb, Ce, La, B, and Si; (2) The coating agent includes at least one of boric acid, metasilicic acid, cobalt hydroxide, niobic acid and tungstic acid; (3) The mass ratio of the lithium-rich material to the coating agent is 1:(0.05%-2%). (4) The conditions for ball milling include: ball milling in an air atmosphere, ball milling frequency of 20 Hz to 50 Hz, and ball milling time of 5 h to 10 h; (5) The annealing temperature is 400℃~800℃, and the annealing time is 1h~10h; (6) Annealing is performed in an air atmosphere; (7) The preparation method of lithium-rich cathode material does not contain liquid phase substances and / or liquid phase reactions.

7. The preparation method according to claim 5 or 6, characterized in that, The method for preparing the lithium-rich material includes the following steps: mixing the lithium-rich material precursor and the lithium source, and performing a first calcination and a second calcination to prepare the lithium-rich material; Optionally, the method for preparing the lithium-rich material satisfies one or more of the following conditions: (1) The lithium source includes lithium carbonate, lithium hydroxide, lithium sulfate, lithium acetate or lithium oxalate; (2) The chemical formula of the lithium-rich material precursor is Ni a Mn b Co c (OH)₂, where 0 ≤ a ≤ 0.5, 0.5 ≤ b ≤ 1, 0 ≤ c ≤ 0.3; (3) The molar ratio of the lithium-rich material precursor to the lithium source is 1:1.04~1.56; (4) The conditions for the first calcination include: a temperature of 400~600℃, and / or a heating rate of 1.0℃ / min~5.0℃ / min, and / or a time of 1h~10h, and / or an environment of air or oxygen atmosphere; (5) The conditions for the second calcination include: a temperature of 600~1000℃, and / or a heating rate of 1.0℃ / min~5.0℃ / min, and / or a time of 6~20h, and / or an environment of air or oxygen atmosphere.

8. A positive electrode sheet, characterized in that, Includes the lithium-rich cathode material as described in any one of claims 1 to 4 or the lithium-rich cathode material prepared by the preparation method described in any one of claims 5 to 7.

9. A lithium-ion battery, characterized in that, Including the positive electrode sheet as described in claim 8.

10. An electrical device, characterized in that, Including the lithium-ion battery as described in claim 9.

Images