Lithium cobalt oxide cathode materials, their preparation methods and applications

Abstract

This application relates to a lithium cobalt oxide cathode material, its preparation method, and its application. The method includes: a substrate and a coating layer located on the surface of the substrate, wherein the substrate and the coating layer form a "sandwich" composite structure lithium cobalt oxide cathode material with a space group of (R-3m)|(P63mc+P63 / mmc)|(R-3m). The solution provided in this application can effectively improve the shortcomings of O3 phase lithium cobalt oxide, exhibiting high capacity, high rate capability, long lifetime, and high safety—the "four highs"—especially demonstrating excellent structural stability and conductivity under high voltage.

Description

Technical Field

[0001] This application relates to the field of lithium cobalt oxide materials technology, and in particular to lithium cobalt oxide cathode materials, their preparation methods and applications. Background Technology

[0002] In recent years, as consumer electronics products such as mobile phones, laptops, and smart wearable devices have developed towards being thinner, lighter, more durable, and faster-charging, higher demands have been placed on the battery performance, lifespan, and fast charging / discharging capabilities. Among these, lithium cobalt oxide, with its excellent volumetric energy density and wide temperature range cycle life, dominates the cathode material market for consumer electronics batteries.

[0003] In related technologies, to achieve higher electrical performance, the voltage window of lithium cobalt oxide is continuously increased, thereby activating more active Li. + It participates in electrochemical reactions to provide higher capacity and voltage. However, this also causes structural instability. Under high voltage, the degree of delithiation on the surface of the delithiated material increases, and the structural phase transition extends from the material surface to the interior of the particles. In addition, the high-valence state Co is unstable, has strong oxidizing properties, and easily reacts with the electrolyte, causing severe gas generation. These factors all lead to a shortened battery cycle life, reduced safety, and affect the practical application of high-voltage lithium cobalt oxide. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this application provides a lithium cobalt oxide cathode material, its preparation method, and its application. This material effectively improves the shortcomings of O3 phase lithium cobalt oxide, exhibiting the "four highs" characteristics of high capacity, high rate capability, long lifespan, and high safety. In particular, it possesses excellent structural stability and conductivity under high voltage.

[0005] The first aspect of this application provides a lithium cobalt oxide cathode material, including a substrate and a coating layer located on the surface of the substrate, wherein the substrate and the coating layer form a "sandwich" composite structure lithium cobalt oxide cathode material having a space group of (R-3m)|(P63mc+P63 / mmc)|(R-3m).

[0006] In some embodiments, X-ray diffraction tests show that the lithium cobalt oxide cathode material has characteristic diffraction peaks on the R-3m space group (003) at (18.9±0.5)°, diffraction peaks on the P63mc space group (002) at (18.6±0.5)°, and diffraction peaks on the P63 / mmc space group (002) at (16.2±0.5)°.

[0007] In some embodiments, the general chemical formula of the matrix is ​​A a C c M mN n O2;

[0008] Wherein, A contains at least the element Li, C contains at least one or more elements from Group I / II other than H and Li, M contains at least the element Co, N contains at least two elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W, 0.9 ≤ a ≤ 1.1, 0 < c / (a+c) ≤ 0.1, 0.8 ≤ m < 1, and 0 < n / (m+n) ≤ 0.15.

[0009] In some embodiments, the general chemical formula of the coating layer is Li. d Na p Co q R r O2;

[0010] Wherein, 0.6 < d + p < 1, 0.6 < d < 0.99, 0 < p < 0.1, 0.8 ≤ q < 1, 0 < r ≤ 0.05, and R contains at least one or more elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W.

[0011] In some embodiments, the coating layer includes a first coating layer located on the surface of the substrate and a second coating layer located on the surface of the first coating layer; the spatial group structures of the first coating layer and the second coating layer are different.

[0012] In some embodiments, the substrate comprises an R-3m space group structure, the first coating layer comprises a P63mc space group structure and a P63 / mmc space group structure, and the second coating layer comprises an R-3m space group structure.

[0013] In some embodiments, the R-3m space group structure of the second coating layer preferentially undergoes a phase transition during heat treatment or electrochemical processes to form Fd-3m and / or Fm-3m space group structures.

[0014] In some embodiments, the substrate diameter is d nm, the thickness of the second coating layer is h1 nm, and the thickness of the first coating layer is h2 nm;

[0015] Where, 3≤h1≤800, 0.015≤h2 / d≤0.15, 3×10 -4 ≤h1 / (d+h2+h1)≤4×10 -2 .

[0016] In some embodiments, in the lithium cobalt oxide cathode material, the molar percentage of the substrate is x%, the molar percentage of the first coating layer is y%, and the molar percentage of the second coating layer is z%.

[0017] Where 60≤x<100, 0<y≤25, 0<z≤15.

[0018] In some embodiments, the lithium cobalt oxide cathode material has a specific surface area of ​​0.15 m². 2 / g ~ 2.2 m 2 / g.

[0019] In some embodiments, the average particle size Dv50 of the lithium cobalt oxide cathode material is 3 μm to 20 μm.

[0020] A second aspect of this application provides a method for preparing a lithium cobalt oxide cathode material, comprising the following steps:

[0021] Sources A, C, M, and N were weighed according to stoichiometric ratios and mixed evenly before undergoing a first sintering treatment to obtain the first compound.

[0022] The Na source, Co source, R source and the first compound were weighed and mixed evenly according to the stoichiometric ratio, and then subjected to a second sintering treatment to obtain the second compound.

[0023] The second compound was added to a solution containing source A to carry out a solution ion exchange reaction. After washing and drying, a third sintering treatment was performed to obtain the above-mentioned lithium cobalt oxide cathode material.

[0024] In some embodiments, the A source is a lithium-containing compound;

[0025] The C source is at least one of the following compounds: sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium.

[0026] The M source is a cobalt-containing compound;

[0027] The N source is at least one of the following: boron, aluminum, nickel, manganese, titanium, zirconium, lanthanum, yttrium, iridium, niobium, and tungsten.

[0028] The R source is at least one of the following compounds: boron, aluminum, nickel, manganese, titanium, zirconium, lanthanum, yttrium, iridium, niobium, and tungsten.

[0029] In some embodiments, the conditions for the first sintering treatment are a temperature of 700°C to 1090°C and a time of 4 hours to 24 hours;

[0030] The conditions for the second sintering treatment are a temperature of 700℃~980℃ and a time of 10h~72h;

[0031] The conditions for the solution ion exchange reaction are a temperature of 65℃~135℃ and a time of 0.5h~60h.

[0032] The conditions for the third sintering treatment are a temperature of 150℃ to 350℃ and a time of 0.1h to 8h.

[0033] In some embodiments, the solution containing source A contains at least two sources A, and the mass ratio of the two sources A is 0.1 to 1.

[0034] In some embodiments, the concentration of the solution containing source A is 2M to 10M.

[0035] A third aspect of this application provides a positive electrode sheet, comprising the aforementioned lithium cobalt oxide positive electrode material.

[0036] A third aspect of this application provides a battery including the aforementioned positive electrode.

[0037] In some embodiments, the charging cut-off voltage of the battery is not less than 4.55V.

[0038] The technical solution provided in this application may include the following beneficial results: a "sandwich" multilayer composite lithium cobalt oxide that simultaneously includes R-3m structure, P63mc structure, and P63 / mmc structure, with R-3m structure as the main component, P63mc structure as the auxiliary component, and also possessing P63 / mmc structure; wherein, the R-3m structure of the outer coating preferentially transforms into the highly structurally stable Fd-3m spinel phase and / or Fm-3m rock salt phase during heat treatment or charge-discharge process, protecting the inner structure from electrolyte erosion, while due to atomic... The oxygen vacancies formed by the rearrangement can effectively capture reactive oxygen released during charge-discharge cycles, mitigating electrolyte oxidation and interfacial side reactions. Simultaneously, the intermediate coating containing P63mc and P63 / mmc structures forms a nano-symbiotic structure. The P63mc structure, containing partially localized coplanar structures of lithium-oxygen octahedra and cobalt-oxygen octahedra, effectively suppresses the migration of Co from octahedral sites to adjacent tetrahedral sites, ensuring crystal structure stability, atomic order, and phase transition reversibility under high voltage. This is suitable for reversible Li-O-O-deintercalation / deintercalation. + It has a large number of layers, high reversible specific capacity, and long cycle life. Furthermore, the interlayer spacing of the P63mc structure is much higher than that of the R-3m structure, resulting in faster Li-ionization. + The insertion / extraction channel exhibits superior ionic and electronic conductivity, resulting in rapid charge / discharge characteristics and outstanding rate performance. The P63 / mmc structure acts as a support during deep lithium extraction from R-3m and P63mc structures, ensuring the stability and reversibility of the overall layered structure, suppressing Co-O interlayer slip and Co / O dissolution. Furthermore, the sodium ions in the P63 / mmc structure provide appropriate local defects and accelerate Li-O extraction. +The insertion / extraction dynamics of the lithium cobalt oxide are observed. The synergistic effect of each layer structure effectively improves the shortcomings of the O3 phase lithium cobalt oxide, exhibiting the "four highs" characteristics of high capacity, high rate capability, long lifetime, and high safety, especially the excellent structural stability and conductivity under high voltage.

[0039] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0040] The above and other objects, features and advantages of this application will become more apparent from the more detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments thereof.

[0041] Figure 1 -A is a schematic diagram of the structure of the lithium cobalt oxide cathode material before charging and discharging, where 3 is the core matrix, including the R-3m space group structure; 2 is the first coating layer, including the P63mc space group structure and the P63 / mmc space group structure; and 1 is the second coating layer, including the R-3m space group structure.

[0042] Figure 1 -B is a schematic diagram of the structure of the lithium cobalt oxide cathode material after charge-discharge cycles, where 3' is the core matrix, including the R-3m space group structure; 2' is the first coating layer, including the P63mc space group structure and the P63 / mmc space group structure; 1' is the second coating layer, including the Fm-3m and / or Fd-3m structures;

[0043] Figure 2 This is the XRD analysis diagram of the lithium cobalt oxide cathode material of Example 1 of this application;

[0044] Figure 3 This is a SEM analysis image of the lithium cobalt oxide cathode material of Example 1 of this application; where A is the core matrix, B is the first coating layer, and C is the second coating layer. Detailed Implementation

[0045] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While embodiments of this application are shown in the drawings, it should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0046] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While the methods and materials described herein, or any equivalent methods and materials, may also be used in the implementation or testing of the invention, preferred methods and materials are now described.

[0047] It should be understood that although the terms “first,” “second,” “third,” etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. Features defined as “first” or “second” may explicitly or implicitly include one or more of that feature. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0048] Where numerical ranges are provided, it should be understood that every intermediate value between the upper and lower limits of the range and any other specified or intermediate value within the specified range is covered within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also covered within the present invention, subject to any explicitly excluded limits within the specified range. Where a specified range includes one or two limits, the range excluding any or both of those included limits is also included within the present invention. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0049] In related technologies, to achieve higher electrical performance, the voltage window of lithium cobalt oxide is continuously being increased, as higher voltages can activate more lattice-active Li. + It participates in electrochemical reactions, thus providing higher capacity and voltage. However, conventional commercial lithium cobalt oxide has a typical hexagonal crystal system with R-3m space group O3 structure. In the O3 structure, oxygen atoms are arranged in an ABCABC hexagonal close-packed pattern, with O atoms forming the basic framework. LiO6 octahedral layers and CoO6 octahedral layers are interspersed within it. This O3 phase lithium cobalt oxide is prone to irreversible cobalt-oxygen dissolution and structural phase transition under high voltage and deep delithiation. The O3 structure gradually transforms into the O1 structure, causing Li... + Serious problems such as loss of active sites, electrolyte oxidation, and interfacial side reactions can lead to shortened battery cycle life, reduced safety, and affect the practical application of high-voltage lithium cobalt oxide, making it difficult to achieve the goal of high-performance lithium battery cathode materials.

[0050] To address the aforementioned issues, this application provides a lithium cobalt oxide cathode material, its preparation method, and its application. This material effectively improves upon the shortcomings of O3 phase lithium cobalt oxide, exhibiting four high characteristics: high capacity, high rate capability, long lifespan, and high safety. In particular, it demonstrates excellent structural stability and conductivity under high voltage.

[0051] The lithium cobalt oxide cathode material provided in this application includes a substrate and a coating layer located on the surface of the substrate. The substrate and the coating layer form a "sandwich" composite structure with a space group of (R-3m)|(P63mc+P63 / mmc)|(R-3m). Specifically, the substrate contains an R-3m space group structure.

[0052] Furthermore, its coating layer includes a first coating layer located on the collective surface and a second coating layer located on the surface of the first coating layer, with different space group structures for the first and second coating layers. That is, a typical "sandwich" composite structure is formed, consisting of a core matrix, an intermediate coating layer, and an outer coating layer. Specifically, the first coating layer contains P63mc and P63 / mmc space group structures, and the second coating layer contains an R-3m space group structure.

[0053] In some specific embodiments, the first and second coating layers are epitaxial structures formed on the substrate surface through solid-state sintering. Therefore, the lithium cobalt oxide cathode material is a lithium cobalt oxide particle with a multilayer epitaxial structure. The lithium cobalt oxide cathode material with a multilayer epitaxial structure exhibits four high characteristics: high capacity, high rate capability, long lifetime, and high safety, making it a high-performance cathode material.

[0054] The coating layer completely covers the surface of the substrate, and the second coating layer uniformly and completely covers the surface of the first coating layer. During charging, discharging or heat treatment, the first coating layer, the substrate and other inner structures are protected from electrolyte erosion, and the battery performance is degraded by electrolyte oxidation and interfacial side reactions.

[0055] Furthermore, in some specific embodiments, the matrix comprises lithium cobalt oxide of the O3 phase with space group R-3m, the first coating layer comprises lithium cobalt oxide of the O2 phase with space group P63mc and sodium cobalt oxide of the P2 phase with space group P63 / mmc, and the second coating layer comprises lithium cobalt oxide of the O3 phase with space group R-3m.

[0056] In some specific embodiments, X-ray diffraction tests show that the lithium cobalt oxide cathode material has characteristic diffraction peaks of the R-3m space group (003) at (18.9±0.5)°, diffraction peaks of the P63mc space group (002) at (18.6±0.5)°, and diffraction peaks of the P63 / mmc space group (002) at (16.2±0.5)°.

[0057] In some specific embodiments, the oxygen layer arrangement of the O3 phase lithium cobalt oxide in the R-3m space group is a hexagonal close-packed ABCABC type, forming a layered structure. Li⁺ and Co³⁺ alternately occupy the octahedral sites on both sides of the oxygen layer, exhibiting high volumetric energy density and excellent ion diffusion channels. The coating layer simultaneously contains both P63mc and P63 / mmc space group structures, enabling nanoscale coexistence of P63mc and P63 / mmc structures. The P63mc space group structure of the O2 phase lithium cobalt oxide has an ABCB type oxygen layer arrangement, containing partially localized coplanar structures of lithium-oxygen octahedra and cobalt-oxygen octahedra. This effectively suppresses the migration of Co from octahedral sites to adjacent tetrahedral sites, ensuring crystal structure stability, atomic arrangement order, and phase transition reversibility under high voltage, and is suitable for reversible Li⁺ insertion / extraction. + It has a large number of layers, high reversible specific capacity, and long cycle life. Furthermore, the interlayer spacing of the P63mc structure is much higher than that of the R-3m structure, resulting in faster Li-ionization. + The insertion / extraction channels exhibit superior ionic and electronic conductivity, resulting in rapid charge / discharge characteristics and outstanding rate performance. The oxygen layer arrangement of the P2 phase sodium cobaltate in the P63 / mmc space group follows an ABBA-type stacking, forming a honeycomb-like interlayer channel. This channel acts as a support during deep lithium extraction in the R-3m and P63mc structures, ensuring the stability and reversibility of the overall layered structure, suppressing Co-O interlayer slip and Co / O dissolution. Furthermore, the sodium ions in the P63 / mmc structure provide in-situ doping of the lithium layer, offering suitable local defects and accelerating Li-O extraction. + The insertion and extraction dynamics of the composite phase lithium cobalt oxide cathode material are observed. Thus, through the synergy between the coating structure and the matrix structure in this "sandwich" composite phase lithium cobalt oxide cathode material, the shortcomings of the current O3 phase lithium cobalt oxide can be effectively improved, exhibiting the "four high" characteristics of high capacity, high rate capability, long lifespan, and high safety. In particular, it demonstrates excellent structural stability and conductivity under high voltage, achieving the goal of a high-performance lithium battery cathode material.

[0058] In some specific embodiments, the R-3m space group structure of the second coating layer preferentially undergoes a phase transition during heat treatment or charge-discharge (i.e., electrochemical) processes, forming Fd-3m and / or Fm-3m space group structures. This comprehensively improves the reversible specific capacity, cycle stability, and fast charge-discharge performance of the O3 phase lithium cobalt oxide. In particular, the preferential phase transition during heat treatment or high-voltage charge-discharge processes to form a high-lattice, highly stable space group structure serves to physically block the electrolyte and mitigate its inward erosion. Simultaneously, the oxygen vacancies formed by atomic rearrangement can effectively capture the active oxygen released during charge-discharge cycles, mitigating electrolyte oxidation and interfacial side reactions, improving cycle capacity retention, and extending battery life.

[0059] As attached Figure 1 As shown, Figure 1-A is a schematic diagram of the lithium cobalt oxide cathode material before charge and discharge, where 3 is the core matrix, including the R-3m space group structure; 2 is the first coating layer, including the P63mc space group structure and the P63 / mmc space group structure; and 1 is the second coating layer, including the R-3m space group structure. When the lithium cobalt oxide cathode material undergoes heat treatment or charge-discharge cycling, the R-3m structure of its second coating layer preferentially undergoes a phase transition, forming... Figure 1 -B shows a schematic diagram of the lithium cobalt oxide cathode material after charge-discharge cycles, where 3' is the core matrix, including the R-3m space group structure; 2' is the first coating layer, including the P63mc space group structure and the P63 / mmc space group structure; and 1' is the second coating layer, including the Fm-3m and / or Fd-3m structures.

[0060] In some specific embodiments, the substrate diameter is d nm, the thickness of the second coating layer is h1 nm, and the thickness of the first coating layer is h2 nm, satisfying: 3 ≤ h1 ≤ 800, 0.015 ≤ h2 / d ≤ 0.15, 3 × 10⁻⁶ -4 ≤h1 / (d+h2+h1)≤4×10 -2 .

[0061] In some specific embodiments, the molar percentages of the core matrix R-3m structure, the intermediate coating material (i.e., the first coating layer P63mc structure and the P63 / mmc structure), and the outer coating material (i.e., the second coating layer R-3m structure) in the overall lithium cobalt oxide cathode material are x%, y%, and z, respectively, satisfying: 60≤x<100, 0<y≤25, 0<z≤15.

[0062] In the lithium cobalt oxide cathode material of this application embodiment, the core matrix accounts for the largest proportion, and the second coating layer on the outer surface is the thinnest. This satisfies the high volumetric energy density of O3 phase lithium cobalt oxide while allowing the outer coating to preferentially transform into the Fd-3m spinel phase and / or Fm-3m rock salt phase, which have strong structural stability, during heat treatment or charge / discharge processes. This protects the inner coating and core matrix, improving the battery's cycle stability and fast charge / discharge performance. However, if the coating layer is too thick, it will affect the Li... + De-embedding.

[0063] In some specific embodiments, the general chemical formula of the matrix is ​​A a C c M m N nO2; wherein, A contains at least Li, C contains at least one or more Group I / II elements other than H and Li, M contains at least Co, and N contains at least two elements selected from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W, with a variability of 0.9 ≤ a ≤ 1.1, 0 < c / (a+c) ≤ 0.1, 0.8 ≤ m < 1, and 0 < n / (m+n) ≤ 0.15. Specifically, C can be selected from at least one element selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra. The matrix material containing the above chemical elements can provide and guarantee the basic electrochemical performance of the battery.

[0064] In some specific embodiments, the general chemical formula of the coating layer is Li. d Na p Co q R r O2; wherein, 0.6 < d + p < 1, 0.6 < d < 0.99, 0 < p < 0.1, 0.8 ≤ q < 1, 0 < r ≤ 0.05, and R contains at least one or more elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W.

[0065] Specifically, the chemical formula of the first coating layer is Li d Na p Co q R r O2; wherein, 0.6 < d + p < 1, 0.6 < d < 0.99, 0 < p < 0.1, 0.8 ≤ q < 1, 0 < r ≤ 0.05, and R contains at least one or more elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W.

[0066] The chemical formula of the second coating layer is Li. d Na p Co q R r O2; wherein, 0.6 < d + p < 1, 0.6 < d < 0.99, 0 < p < 0.1, 0.8 ≤ q < 1, 0 < r ≤ 0.05, and R contains at least one or more elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W.

[0067] The first and second coating layers share the same general chemical formula, but their structures are different. The first coating layer, i.e. the intermediate coating, contains both P63mc and P63 / mmc structures, while the second coating layer, i.e. the outer coating, contains an R-3m structure. During heat treatment or high-voltage charge and discharge, it preferentially undergoes a phase transition to form a Fd-3m structure and / or an Fm-3m structure with strong lattice stability.

[0068] It should be noted that the lithium cobalt oxide cathode material in this application embodiment is due to the different epitaxial structures of the intermediate layer coating and the outer layer coating. By utilizing multi-structure composite technology, the intermediate layer coating, which combines the P63mc structure and the P63 / mmc structure, provides sufficient high voltage structural stability and ionic / electronic conductivity. The R-3m structure of the outer layer coating can be transformed into a highly stable Fd-3m structure and / or Fm-3m structure during heat treatment or charge-discharge process, thereby protecting the inner layer structure, improving the stability of the inner layer structure, and comprehensively improving the reversible specific capacity, cycle stability, fast charge and fast discharge performance of O3 phase lithium cobalt oxide.

[0069] In some specific embodiments, the specific surface area of ​​the lithium cobalt oxide cathode material is 0.15 m². 2 / g ~ 2.2 m 2 / g. For example, 0.15 m 2 / g, 0.16 m 2 / g, 0.17 m 2 / g, 0.18m 2 / g, 0.19 m 2 / g, 0.20m 2 / g, 0.21 m 2 / g、2.2 m 2 / g, or any value within the above range.

[0070] In some specific embodiments, the average particle size Dv50 of the lithium cobalt oxide cathode material is 3 μm to 20 μm. Specifically, for example, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc., or any value within the above range.

[0071] In practical applications, the lithium cobalt oxide cathode material in the cathode sheet can be selected from particles of any size in the above-mentioned 3μm ~ 20μm materials, or several lithium cobalt oxide cathode materials with different particle sizes in the above-mentioned particle size range can be mixed in a certain proportion as the lithium cobalt oxide cathode material added to the cathode sheet.

[0072] This application also provides a method for preparing lithium cobalt oxide cathode material, which forms a "sandwich" composite phase lithium cobalt oxide cathode material with a multilayer epitaxial structure by solid-state sintering treatment on the substrate surface.

[0073] Specifically, the preparation method includes the following steps:

[0074] 1) Weigh and mix the A source, C source, M source, and N source according to their stoichiometric ratios, and then perform a first sintering treatment to obtain the first compound;

[0075] 2) The Na source, Co source, R source and the first compound are weighed and mixed evenly according to the stoichiometric ratio, and then subjected to a second sintering treatment to obtain the second compound;

[0076] 3) The second compound was added to a solution containing source A to carry out a solution ion exchange reaction. After washing and drying, a third sintering treatment was carried out to obtain a "sandwich" composite phase lithium cobalt oxide cathode material with a multilayer epitaxial structure.

[0077] In step 1), sources A, C, M, and N are weighed and mixed uniformly according to their stoichiometric ratios, i.e., according to the general chemical formula of the matrix A. a C c M m N n O2 is selected within the specified stoichiometric ratio to mix a certain mass of compounds, where 0.9≤a≤1.1, 0<c / (a+c)≤0.1, 0.8≤m<1, and 0<n / (m+n)≤0.15.

[0078] In step 1), source A is a lithium-containing compound. It may include one or more compounds selected from lithium acetate, lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, lithium sulfate, and lithium bromide.

[0079] The C source in step 1) is at least one of the following compounds: sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium. Specifically, it can be one or more of the following: acetate, carbonate, hydroxide, nitrate, chloride, sulfate, and bromide.

[0080] The M source in step 1) is a cobalt-containing compound. It may include one or more of cobalt(II) oxide, cobalt(III) oxide, cobalt(II) hydroxide, cobalt(II) hydroxyl oxide, cobalt(II) carbonate, cobalt(II) acetate, cobalt(II) sulfate, cobalt(II) nitrate, and cobalt(II) chloride.

[0081] The N source in step 1) is at least one of the following compounds: boron, aluminum, nickel, manganese, titanium, zirconium, lanthanum, yttrium, iridium, niobium, and tungsten. Specifically, it can be one or more of the following: oxides, hydroxides, carbonates, acetates, sulfates, nitrates, chlorides, and oxyacids.

[0082] The conditions for the first sintering treatment are a temperature of 700℃~1090℃ and a time of 4h~24h; preferably, a sintering treatment at 860℃~980℃ for 10h~18h; more preferably, a sintering treatment at 900℃~960℃ for 15h~16h.

[0083] In step 2), the Na source, Co source, R source, and the first compound are weighed and mixed thoroughly according to stoichiometric ratios. At this point, the coating layer is coated according to the general chemical formula Li. d Na p Co q R rWithin the specified stoichiometric ratio of O2 and the proportion of the core matrix, a certain mass of a compound is selected and mixed with the first compound, wherein the general chemical formula of the coating layer is Li. d Na p Co q R r In O2, 0.6<d+p<1, 0.6<d<0.99, 0<p<0.1, 0.8≤q<1, 0<r≤0.05.

[0084] In step 2), the Na source is a sodium-containing compound. It may include one or more of sodium acetate, sodium carbonate, sodium hydroxide, sodium nitrate, sodium chloride, sodium sulfate, and sodium bromide.

[0085] The Co source in step 2) is a cobalt-containing compound. It may include one or more of cobalt(II) oxide, cobalt(III) oxide, cobalt(II) hydroxide, cobalt(II) hydroxyl oxide, cobalt(II) carbonate, cobalt(II) acetate, cobalt(II) sulfate, cobalt(II) nitrate, and cobalt(II) chloride.

[0086] The R source in step 2) is at least one compound containing boron, aluminum, nickel, manganese, titanium, zirconium, lanthanum, yttrium, iridium, niobium, or tungsten. Specifically, it can be one or more of the oxides, hydroxides, carbonates, acetates, sulfates, nitrates, chlorides, or oxyacids of the above elements.

[0087] The conditions for the second sintering treatment are a temperature of 700℃~980℃ and a time of 10h~72h; preferably, a sintering treatment at 750℃~900℃ for 15h~48h; more preferably, a sintering treatment at 780℃~820℃ for 24h~30h.

[0088] Step 3) may specifically include:

[0089] 3.1) Prepare an aqueous solution containing source A, then add the second compound to the solution to carry out a solution ion exchange reaction, wash and dry to obtain the third compound;

[0090] 3.2) The third compound is subjected to a third sintering treatment to obtain a "sandwich" composite phase lithium cobalt oxide cathode material with a multilayer epitaxial structure.

[0091] In step 3.1), the aqueous solution containing source A contains at least two sources A, and the mass ratio of the two sources A is 0.1 to 1. Specific examples include 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc., or any value within the above range.

[0092] In step 3.1), the salt concentration in the aqueous solution containing source A is 2M to 10M. Specifically, for example, 2M, 3M, 4M, 5M, 6M, 7M, 8M, 9M, 10M, or any value within the above range.

[0093] In step 3.1), the conditions for the solution ion exchange reaction are a temperature of 65℃~135℃ and a time of 0.5h~60h; preferably, treatment at 75℃~120℃ for 15h~48h; more preferably, treatment at 850℃~100℃ for 18h~24h.

[0094] The conditions for the third sintering treatment in step 3.2) are a temperature of 150℃~350℃ and a time of 0.1h~8h; preferably, a sintering treatment at 100℃~300℃ for 0.5h~5h; more preferably, a sintering treatment at 250℃~290℃ for 2h~3h.

[0095] In this embodiment, through the control of parameters in heat treatment processes and ion exchange processes under different conditions, particularly the addition ratio of O3 phase lithium cobalt oxide (i.e., the first compound) to Na, Co, and R sources in step 2), the concentration and ratio of A source in the ion exchange process in step 3.1), and the parameters of the third sintering process in step 3.2), a multilayer epitaxial structure coated on the substrate surface is finally obtained. The P63 / mmc structure, which coexists with the P63mc structure nanostructure, acts as a support during the deep delithiation of the R-3m and P63mc structures, ensuring the stability and reversibility of the overall layered structure, inhibiting Co-O interlayer slip and Co / O dissolution. Furthermore, the sodium ions in the P63 / mmc structure are in-situ doped into the lithium layer, providing appropriate local defects and accelerating Li... + The insertion / extraction kinetics of the outer layer are observed. During charge and discharge, the R-3m structure of the outer layer preferentially transforms into the structurally stable Fd-3m spinel phase and / or Fm-3m rock salt phase, protecting the inner structure of the outer coating from electrolyte erosion. Simultaneously, the oxygen vacancies formed by atomic rearrangement effectively capture the active oxygen released from the inner layer of the outer coating during charge and discharge cycles, mitigating electrolyte oxidation and interfacial side reactions. Therefore, by controlling parameters in the heat treatment and ion exchange processes, the shortcomings of O3 phase lithium cobalt oxide can be comprehensively improved. Through multi-faceted synergy, this cathode material exhibits the "four highs" characteristics of high capacity, high rate capability, long lifetime, and high safety, especially its excellent structural stability and conductivity under high voltage.

[0096] Furthermore, the preparation method of this application embodiment is simple and easy to operate, and the introduced elements are low in cost, reducing pollution and cost. It is suitable for large-scale production and has extremely high industrial production application value.

[0097] This application also provides a positive electrode sheet, which includes the above-mentioned lithium cobalt oxide positive electrode material.

[0098] Specifically, the positive electrode may include a positive current collector and a positive electrode material layer disposed on the positive current collector, the positive electrode material layer including the aforementioned lithium cobalt oxide positive electrode material. The positive current collector is a conventional metal foil or a composite current collector, such as aluminum foil.

[0099] In some specific embodiments, the positive electrode material layer is formed by coating the surface of the positive electrode current collector with a positive electrode slurry. The positive electrode slurry includes, in addition to the aforementioned lithium cobalt oxide positive electrode material, conductive agents and binders. This application does not specifically limit the types of conductive agents and binders; they can be selected according to actual needs. As examples, conductive agents include, but are not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; binders include, but are not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0100] The lithium cobalt oxide cathode material, conductive agent, and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to obtain a uniform cathode slurry. The cathode slurry is then uniformly coated onto the cathode current collector, and the cathode sheet is obtained through processes such as drying, rolling, and compaction.

[0101] This application also provides a battery comprising the above-described positive electrode plate.

[0102] Specifically, the battery can be a lithium-ion battery.

[0103] The battery in this embodiment has a charging cut-off voltage of not less than 4.55V.

[0104] In some specific embodiments, the battery includes an electrolyte, a separator, and a negative electrode, in addition to the positive electrode. The negative electrode, separator, and positive electrode are sequentially stacked and then formed into a battery cell using a winding or stacking process. The battery cell is then placed into a pre-formed aluminum-plastic film, baked, and then the electrolyte is injected into the baked and dried cell, immersing it in the electrolyte. Following vacuum sealing, settling, and formation processes, the battery manufacturing is complete.

[0105] The electrolyte, separator, and negative electrode can all be made from any known materials, and this application does not limit them.

[0106] As an example, the separator described in the embodiments of the present application can be arbitrarily selected from known porous structure separators with good chemical stability and mechanical stability. The material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without any particular limitation.

[0107] As an example, the electrolyte described in the embodiments of the present application can be selected from electrolytes containing a solvent, an additive, and a lithium salt. Among them, the lithium salt can be selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)imide, lithium difluorooxalate phosphate, and lithium perchlorate. The concentration of the lithium salt in the electrolyte is 0.9 mol / L to 1.3 mol / L. The solvent can be selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate, and the carboxylic ester solvent can be selected from one or more of ethyl propionate, ethyl acetate, and propyl propionate. The additive can be selected from one or more of ethylene carbonate, vinylene carbonate, ethylene ethylenecarbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, and difluoroethylene carbonate. The components can be freely combined, without any particular limitation.

[0108] As an example, the negative electrode sheet described in the embodiments of the present application can be a lithium metal thin sheet.

[0109] As an example, the negative electrode sheet described in the embodiments of the present application can also include a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector. Among them, the negative electrode current collector uses a conventional metal foil or a composite current collector, for example, a copper foil can be used. The negative electrode material layer is formed by coating a negative electrode paste on the surface of the negative electrode current collector. The negative electrode paste includes a negative electrode active material, a conductive agent, and a binder. The embodiments of the present application do not specifically limit the types of the negative electrode active material, the conductive agent, and the binder, and can be selected according to actual needs. As an example, the negative electrode active material can be natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO k (0 < k < 2, such as k = 1), LiSn alloy, LiSnO alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12One or more of LiAl alloy and lithium metal; the conductive agent can be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder can be one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), waterborne acrylic resin and carboxymethyl cellulose (CMC).

[0110] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material, conductive agent, and binder are dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto the negative electrode current collector, and after drying, rolling, and compaction, the negative electrode sheet is obtained.

[0111] This application does not impose any particular restrictions on the application areas of the battery, and it can be used in consumer electronics products, new energy vehicle-grade energy storage, and other fields.

[0112] To make the present invention easier to understand, the present application will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present application. Unless otherwise specified, the raw materials or components used in the present application can be obtained commercially or by conventional methods.

[0113] Example 1

[0114] 1) Weigh out lithium carbonate (source A), cobalt tetroxide (source M), magnesium carbonate (source C), and aluminum oxide, yttrium oxide, and lanthanum oxide (source N) in a molar ratio (Li:Co:Mg:Al:Y:La=104:95:1:3:1:1) and mix them evenly in a planetary ball mill at a speed of 1200 r / min. Then transfer the mixed powder to a box furnace and heat it to 960°C at a heating rate of 3°C / min. Sinter it in air for 15 h. After the reaction is complete, cool it to room temperature and grind and sieve it to obtain O3 phase lithium cobalt oxide.

[0115] 2) Weigh out the above-mentioned O3 phase lithium cobalt oxide with Na source sodium carbonate, Co source cobalt tetroxide and R source (alumina, yttrium oxide) in a molar ratio (LCO:Na:Co:Al:Y=675:82:96:3:1), and in a planetary ball mill, at a speed of 1200 r / min for 2 min, repeat 3 times until the powder is uniformly mixed. Then transfer it to a box furnace and heat it to 820℃ at a heating rate of 3℃ / min. Sinter it in air atmosphere for 24 h. After the reaction is completed, cool it to room temperature, grind and sieve it to obtain O3 phase lithium cobalt oxide coated with P2 phase sodium cobalt oxide.

[0116] 3) Take lithium hydroxide and lithium chloride of source A in a molar ratio of 1:1 and prepare a lithium-containing aqueous solution with a concentration of 6M. Add the O3 phase lithium cobalt oxide coated with the above P2 phase sodium cobalt oxide to the above lithium-containing aqueous solution, and stir thoroughly in a reactor at 85°C and react at high temperature for 24 hours. After the reaction is completed, wash with water and dry (oven drying temperature and time are 80°C and 15 hours, respectively) to obtain O3 phase lithium cobalt oxide co-coated with O2 phase and P2 phase.

[0117] 4) Finally, the co-coated O3 phase lithium cobalt oxide was heated to 290°C in a box furnace at a heating rate of 5°C / min and sintered in air for 0.5h to obtain a lithium cobalt oxide cathode material with a multilayer epitaxial structure (R-3m)|(P63mc+P63 / mmc)|(R-3m) "sandwich" composite structure.

[0118] Example 2

[0119] The difference from Example 1 lies in the amount of each raw material added in step 2).

[0120] Example 2A: The molar ratio of O3 phase lithium cobalt oxide to Na source, Co source and R source in Example 1 is adjusted to (LCO:Na:Co:Al:Y=300:82:96:3:1), and other operations and parameters are the same as in Example 1.

[0121] Example 2B: The molar ratio of O3 phase lithium cobalt oxide to Na source, Co source and R source in Example 1 is adjusted to (LCO:Na:Co:Al:Y=1425:82:96:3:1), and other operations and parameters are the same as in Example 1.

[0122] Example 2C: The molar ratio of O3 phase lithium cobalt oxide to Na source, Co source and R source in Example 1 is adjusted to (LCO:Na:Co:Al:Y=175:82:96:3:1), and other operations and parameters are the same as in Example 1.

[0123] Example 3

[0124] The difference from Example 1 is the proportion of source A in the lithium-containing aqueous solution in step 3).

[0125] Example 3A: The ratio of lithium hydroxide and lithium chloride in source A in Example 1 was adjusted to 9:1, and other operations and parameters were the same as in Example 1.

[0126] Example 4

[0127] The difference from Example 1 is the salt concentration of the lithium-containing aqueous solution in step 3).

[0128] Example 4A: The salt concentration in the lithium-containing aqueous solution in Example 1 was adjusted to 2M, and other operations and parameters were the same as in Example 1.

[0129] Example 4B: The salt concentration in the lithium-containing aqueous solution in Example 1 was adjusted to 10M, and other operations and parameters were the same as in Example 1.

[0130] Example 5:

[0131] The difference from Example 1 lies in step 4), which involves the sintering process of the O3 phase lithium cobalt oxide coated with the co-coated material.

[0132] Example 5A: The sintering temperature of the co-coated O3 phase lithium cobalt oxide described in Example 1 in the box furnace was adjusted to 350°C, and other operations and parameters were the same as in Example 1.

[0133] Example 5B: The sintering temperature of the co-coated O3 phase lithium cobalt oxide described in Example 1 in the box furnace was adjusted to 150°C, and other operations and parameters were the same as in Example 1.

[0134] Example 5C: The sintering time of the co-coated O3 phase lithium cobalt oxide described in Example 1 in the box furnace was adjusted to 8 hours, and other operations and parameters were the same as in Example 1.

[0135] Example 5D: The sintering time of the co-coated O3 phase lithium cobalt oxide described in Example 1 in the box furnace was adjusted to 0.1 h, and other operations and parameters were the same as in Example 1.

[0136] Comparative Example 1

[0137] Weigh out lithium carbonate (source A), cobalt tetroxide (source M), magnesium carbonate (source C), and aluminum oxide, yttrium oxide, and lanthanum oxide (source N) in a molar ratio (Li:Co:Mg:Al:Y:La=104:95:1:3:1:1) and mix them evenly in a planetary ball mill at a speed of 1200 r / min. Then, transfer the mixed powder to a box furnace and heat it to 960°C at a heating rate of 3°C / min. Sinter it in air for 15 h. After the reaction is complete, cool it to room temperature, grind it, and sieve it to obtain O3 phase lithium cobalt oxide.

[0138] Comparative Example 2

[0139] Lithium carbonate (source A), cobalt tetroxide (source M), magnesium carbonate (source C), and aluminum oxide, yttrium oxide, and lanthanum oxide (source N) were weighed in a molar ratio (Li:Co:Mg:Al:Y:La=104:95:1:3:1:1) and mixed evenly in a planetary ball mill at a speed of 1200 r / min. The mixed powder was then transferred to a box furnace and heated to 960°C at a heating rate of 3°C / min. The mixture was sintered in air for 15 h. After the reaction was completed, the mixture was cooled to room temperature, ground, and sieved to obtain O3 phase lithium cobalt oxide.

[0140] The above-mentioned O3 phase lithium cobalt oxide, sodium carbonate from Na source, cobalt tetroxide from Co source, and R source (alumina and yttrium oxide) were weighed out in a molar ratio (LCO:Na:Co:Al:Y=1575:82:96:3:1) and milled in a planetary ball mill at a speed of 1200 r / min for 2 min. This process was repeated 3 times until the powder was uniformly mixed. Then, the mixture was transferred to a box furnace and heated to 820°C at a heating rate of 3°C / min. The mixture was sintered in air for 24 h. After the reaction was completed, the mixture was cooled to room temperature and then ground and sieved to obtain the target product.

[0141] Comparative Example 3

[0142] Weigh out lithium carbonate (source A), cobalt tetroxide (source M), magnesium carbonate (source C), and aluminum oxide, yttrium oxide, and lanthanum oxide (source N) in a molar ratio (Li:Co:Mg:Al:Y:La=104:95:1:3:1:1) and mix them evenly in a planetary ball mill at a speed of 1200 r / min. Then, transfer the mixed powder to a box furnace and heat it to 960°C at a heating rate of 3°C / min. Sinter it in air for 15 h. After the reaction is complete, cool it to room temperature, grind it, and sieve it to obtain O3 phase lithium cobalt oxide.

[0143] Then, lithium hydroxide and lithium chloride of source A with a molar ratio of 1:1 were prepared into a 6M lithium-containing aqueous solution. The above-mentioned O3 phase lithium cobalt oxide was added to the above lithium-containing aqueous solution, and the mixture was stirred thoroughly in a reactor at 85°C and reacted at high temperature for 24 hours. After the reaction was completed, the mixture was washed with water and dried (oven drying temperature and time were 80°C and 15 hours, respectively). Then, the mixture was heated to 290°C in a box furnace at a heating rate of 5°C / min and sintered in air atmosphere for 0.5 hours to obtain the target product.

[0144] Physicochemical property testing

[0145] The physicochemical properties of the lithium cobalt oxide cathode materials prepared in the above embodiments and comparative examples were tested.

[0146] 1) X-ray diffraction (XRD) tests were performed on the lithium cobalt oxide cathode materials of Example 1 and Comparative Example 1. The test results are shown in the attached figure. Figure 2 As shown.

[0147] 2) The lithium cobalt oxide cathode material of Example 1 was subjected to scanning electron microscopy (SEM). The test results are attached. Figure 3 As shown.

[0148] 3) Particle size and specific surface area (SSA) tests were performed on the lithium cobalt oxide cathode materials of the examples and comparative examples. The test results are shown in Table 1. Among them, the particle size test was performed according to "GB / T 19077-2016 Particle Size Analysis by Laser Diffraction"; the specific surface area test was performed according to "GB / T 19587-2017 Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method".

[0149] Table 1

[0150]

[0151] Analysis based on the attached diagram:

[0152] like Figure 1 , Figure 2 and Figure 3 As shown, the lithium cobalt oxide cathode material of Example 1 has a multilayer epitaxial structure compared with the comparative example. Specifically, it includes a matrix, a first coating layer and a second coating layer, and simultaneously contains three space group XRD characteristic peaks: R-3m, P63mc and P63 / mmc. It is a "sandwich" composite structure lithium cobalt oxide cathode material.

[0153] Referring to the accompanying drawings and Table 1, the lithium cobalt oxide cathode material prepared by the method of the embodiments has conventional specific surface area, particle size and morphology, which are comparable to the specific surface area and particle size of lithium cobalt oxide cathode materials prepared by conventional methods, such as those of Comparative Examples 1-3, and can be applied to cathode plates.

[0154] The lithium cobalt oxide cathode materials prepared in the above embodiments and comparative examples were used to make positive electrode sheets, and then combined with negative electrode sheets, electrolytes, separators, etc. to form lithium-ion batteries. The electrochemical performance of the lithium-ion batteries was tested to observe the influence of the lithium cobalt oxide cathode material on the electrochemical performance of the batteries.

[0155] Application examples

[0156] The lithium cobalt oxide cathode material prepared by the methods of the above embodiments and comparative examples was mixed with the conductive agent acetylene black and the binder PVDF (polyvinylidene fluoride) at a mass ratio of 94:3:3. The mixture was thoroughly stirred in N-methylpyrrolidone solvent to form a uniform cathode slurry. The cathode slurry was uniformly coated onto the cathode current collector Al foil, and after drying, rolling, and compaction, it was cut into cathode sheets with a diameter of 12 mm.

[0157] The above positive electrode sheet is then combined with a lithium metal sheet as the negative electrode, a polypropylene (PP) membrane as the separator, and an EC / EMC / DMC solution containing 1M LiPF6 (volume ratio 1:2:2) as the electrolyte, and assembled into a button cell in an argon-filled glove box.

[0158] Electrochemical performance testing

[0159] 1) In a (25±2)℃ constant temperature chamber, lithium-ion batteries were charged at a constant current and constant voltage of 0.1C to a cutoff voltage of 4.6V, with a cutoff current of 0.05C, and then discharged at a constant current of 0.1C to a cutoff voltage of 3V. The reversible specific capacity and coulombic efficiency of the batteries in the first cycle were measured. Five batteries were used in each group, and the average test results were recorded in Table 2. The batteries were then charged at a constant current and constant voltage of 3C to a cutoff voltage of 4.6V, with a cutoff current of 0.05C, and then discharged at a constant current of 3C to a cutoff voltage of 3V. The reversible specific capacity of the batteries in the first cycle was measured. Five batteries were used in each group, and the average test results were recorded in Table 2.

[0160] 2) In a constant temperature chamber at (45±2)℃, charge the lithium-ion battery to 4.6V at a constant current and constant voltage of 0.1C, cut off the current at 0.05C, and then discharge it to 3V at 0.1C. Repeat this charge-discharge cycle multiple times. Calculate the capacity retention rate of the battery after 50 cycles. For each group of 5 batteries, take the average value of the test results and fill it in Table 2.

[0161] Capacity retention (%) = Discharge specific capacity after 50 cycles (mAh / g) / Discharge specific capacity after the first cycle (mAh / g) × 100%

[0162] Table 2

[0163]

[0164] Data from the application examples show that when the lithium cobalt oxide cathode material of Example 1 is applied to a lithium-ion battery, under conditions of 25°C and 3-4.6V, the specific capacity and coulombic efficiency at 0.1C first-cycle discharge are as high as 210.5 mAh / g and 95.2%, respectively, which is superior to Comparative Example 1's 203.2 mAh / g and 92.9%, Comparative Example 2's 176.4 mAh / g and 87.1%, and Comparative Example 3's 187.4 mAh / g and 81.8%. In particular, it still has a reversible specific capacity of 176.5 mAh / g under the high current density discharge condition of 3.0C, which is 14.1 mAh / g higher than Comparative Example 1, 32.6 mAh / g higher than Comparative Example 2, and 26.4 mAh / g higher than Comparative Example 3. Moreover, the capacity retention rate after 50 cycles at 0.1C and 45°C is 80.3%, which is far superior to Comparative Example 1's 68.2%, Comparative Example 2's 65.0%, and Comparative Example 3's 62.4%.

[0165] Clearly, the lithium cobalt oxide cathode material shown in the embodiments of this application exhibits excellent reversible specific capacity, rate performance, and cycle stability when applied to lithium-ion batteries. This is attributed to the perfectly positioned heteroepitaxial structure coated on the substrate surface. In contrast, the lithium cobalt oxide cathode materials prepared using methods described in Comparative Examples 1-3, including only one sintering process, no ion exchange process, or only two sintering processes, cannot simultaneously achieve the "four high" characteristics of high capacity, high rate performance, long lifespan, and high safety. Especially under 3.0C high current density discharge conditions or 45°C high-temperature cycling conditions, their performance deteriorates rapidly, severely impacting the lifespan of lithium-ion batteries.

[0166] Test data from Examples 1 and 2 show that after adjusting the coating material of the lithium cobalt oxide cathode material, it still has good reversible specific capacity and first-cycle coulombic efficiency. However, when the content of O3 phase lithium cobalt oxide is too low, or the content of N source, Co source or R source is too high, it will affect the high-temperature cycle capacity retention rate of the battery.

[0167] Test data from Examples 1, 3, and 4 show that after adjusting the materials and salt concentration of the lithium-containing aqueous solution in the ion exchange treatment step, excessively low or high salt concentration in the lithium-containing aqueous solution can affect the rate performance and high-temperature cycling performance of the battery.

[0168] Test data from Examples 1 and 5 show that after adjusting the process parameters of the third sintering process, if the sintering temperature is too high or the sintering time is too long, it will affect the rate performance and cycle performance of the lithium cobalt oxide cathode material when it is used in lithium-ion batteries.

[0169] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A lithium cobalt oxide cathode material, characterized in that: Includes a substrate and a coating layer located on the surface of the substrate; The general chemical formula of the matrix is ​​A a C c M m N n O2; wherein A contains at least Li, C contains at least one or more first / second group elements other than H and Li, M contains at least Co, N contains at least two elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W, 0.9 ≤ a ≤ 1.1, 0 < c / (a+c) ≤ 0.1, 0.8 ≤ m < 1, and 0 < n / (m+n) ≤ 0.15; The chemical formula of the coating layer is Li d Na p Co q R r O2; where 0.6 < d + p < 1, 0.6 < d < 0.99, 0 < p < 0.1, 0.8 ≤ q < 1, 0 < r ≤ 0.05, and R contains at least one or more elements from B, Al, Ni, Mn, Ti, Zr, La, Y, Ir, Nb, and W; The substrate and the coating layer form a "sandwich" composite lithium cobalt oxide cathode material with a space group of (R-3m)|(P63mc+P63 / mmc)|(R-3m). The coating layer includes a first coating layer on the surface of the substrate and a second coating layer on the surface of the first coating layer. The space group structures of the first and second coating layers are different. The substrate contains an R-3m space group structure, the first coating layer contains both P63mc and P63 / mmc space group structures, and the second coating layer contains an R-3m space group structure. The R-3m space group structure of the second coating layer preferentially undergoes a phase transition during thermal treatment or electrochemical processes, forming an Fd-3m and / or Fm-3m space group structure.

2. The lithium cobalt oxide cathode material according to claim 1, characterized in that: X-ray diffraction tests revealed that the lithium cobalt oxide cathode material exhibits characteristic diffraction peaks on the R-3m space group (003) at (18.9±0.5)°, on the P63mc space group (002) at (18.6±0.5)°, and on the P63 / mmc space group (002) at (16.2±0.5)°.

3. The lithium cobalt oxide cathode material according to claim 1, characterized in that: The substrate has a diameter of d nm, the second coating layer has a thickness of h1 nm, and the first coating layer has a thickness of h2 nm; Where, 3≤h1≤800, 0.015≤h2 / d≤0.15, 3×10 -4 ≤h1 / (d+h2+h1)≤4×10 -2 .

4. The lithium cobalt oxide cathode material according to claim 1, characterized in that: In the lithium cobalt oxide cathode material, the molar percentage of the substrate is x%, the molar percentage of the first coating layer is y%, and the molar percentage of the second coating layer is z%. Where 60≤x<100, 0<y≤25, 0<z≤15.

5. The lithium cobalt oxide cathode material according to claim 1, characterized in that: The specific surface area of ​​the lithium cobalt oxide cathode material is 0.15 m². 2 / g ~ 2.2 m 2 / g; And / or, the average particle size Dv50 of the lithium cobalt oxide cathode material is 3 μm ~ 20 μm.

6. A method for preparing a lithium cobalt oxide cathode material, characterized in that, Includes the following steps: Sources A, C, M, and N were weighed according to stoichiometric ratios and mixed evenly before undergoing a first sintering treatment to obtain the first compound. The Na source, Co source, R source and the first compound were weighed and mixed evenly according to the stoichiometric ratio, and then subjected to a second sintering treatment to obtain the second compound. The second compound is added to a solution containing source A to carry out a solution ion exchange reaction. After washing and drying, a third sintering treatment is performed to obtain the lithium cobalt oxide cathode material as described in any one of claims 1 to 5.

7. The preparation method according to claim 6, characterized in that: The source A is a lithium-containing compound; The C source is at least one of the following compounds: sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium. The M source is a cobalt-containing compound; The N source is at least one of the following: boron, aluminum, nickel, manganese, titanium, zirconium, lanthanum, yttrium, iridium, niobium, and tungsten. The R source is at least one of the following compounds: boron, aluminum, nickel, manganese, titanium, zirconium, lanthanum, yttrium, iridium, niobium, and tungsten.

8. The preparation method according to claim 6, characterized in that: The conditions for the first sintering treatment are a temperature of 700℃~1090℃ and a time of 4h~24h; The conditions for the second sintering treatment are a temperature of 700℃~980℃ and a time of 10h~72h; The conditions for the solution ion exchange reaction are a temperature of 65℃~135℃ and a time of 0.5h~60h. The conditions for the third sintering treatment are a temperature of 150℃ to 350℃ and a time of 0.1h to 8h.

9. The preparation method according to claim 6, characterized in that: The solution containing source A contains at least two sources A, and the mass ratio of the two sources A is 0.1 to 1.

10. The preparation method according to claim 6, characterized in that: The concentration of the solution containing source A is 2M~10M.

11. A positive electrode plate, characterized in that, The lithium cobalt oxide cathode material includes the lithium cobalt oxide cathode material according to any one of claims 1 to 5 or the lithium cobalt oxide cathode material prepared by any one of claims 6 to 10.

12. A battery, characterized in that, Includes the positive electrode sheet as described in claim 11.

13. The battery according to claim 12, characterized in that: The charging cutoff voltage of the battery is not lower than 4.55V.

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