Core-shell structured cathode material, method for preparing the same, battery cathode, and secondary battery

Abstract

The application relates to a core-shell structure positive electrode material, which comprises a core and an outer coating layer, from the core to the outside, the outer coating layer comprises an electrolyte layer and a reinforcing layer in sequence, the material of the core comprises a ternary positive electrode material, the electrolyte layer comprises a metal phosphate with a chemical formula of Li a M1 b M2 c (PO4)3, 0 The application also relates to a preparation method of the core-shell structure positive electrode material, which is simple in operation and easy to realize large-scale production. The application further relates to a battery positive electrode, a secondary battery and an electric device comprising the above core-shell structure positive electrode material, which have excellent rate performance and cycle stability.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, specifically to a core-shell structured cathode material, its preparation method, a battery cathode, and a secondary battery. Background Technology

[0002] Lithium-ion technology has changed the traditional communication methods and the power supply methods of portable devices, and is driving a revolution in global transportation and energy supply. In the field of electric vehicles, the cycle life and high-temperature storage performance of batteries are two important indicators for evaluating the performance of batteries and materials. Among them, the cathode material in the battery system is the decisive factor. In the existing cathode material system, ternary materials are widely used due to their advantages of high specific energy density and good cycle performance. As we all know, with the charging and discharging of the battery, especially in the high-temperature environment, the electrochemical performance of the cathode material in the battery will be greatly reduced. The main reasons can be summarized as follows: (1) At high temperature, Ni 4+ and Li + (1) The reaction with the electrolyte leads to an increase in interfacial impedance and cycle DCR, as well as a decrease in capacity; (2) The HF generated by the electrode / electrolyte interface reaction further corrodes the interface, leading to the dissolution of surface Ni / Co / Mn metals, causing surface lattice reconstruction, which has an adverse effect on the structure and electrochemical performance of the material.

[0003] To improve the stability of the battery electrode / electrolyte interface, metal oxide coating methods are currently commonly used, employing inert nano-inorganic oxides (such as aluminum oxide, magnesium oxide, titanium oxide, and zinc oxide) to coat materials in a solid-state manner. However, existing large-scale coating technologies have the following shortcomings: (1) The resulting coating layer is usually distributed in a dot-like or island-like shape, with uneven interface thickness and incomplete coverage, resulting in poor electrochemical performance of the battery when used at high temperatures; (2) The nano-oxide coating layer structure of conventional solid-state processes is loose, easily reacting with HF to form new exposed interfaces, leading to the dissolution of transition metals, causing continuous structural deterioration and performance degradation at the interface, thereby reducing the cycle performance and rate performance of the material.

[0004] Traditional phosphate-coated cathode materials can improve the cycle stability of the material, but the rate performance of the material still needs to be improved, and the capacity decay over longer cycles still needs further optimization. Summary of the Invention

[0005] In view of this, one of the objectives of this application is to provide a core-shell structured cathode material that can be used to prepare secondary battery cathodes and improve the rate performance and cycle stability of the battery.

[0006] The first aspect of this application provides a core-shell structured cathode material, comprising a core and an outer coating layer, wherein, from the core outward, the outer coating layer sequentially comprises an electrolyte layer and a reinforcing layer;

[0007] The core material includes ternary cathode material;

[0008] The electrolyte layer comprises Li a M1 b M2 c Metal phosphates of (PO4)3, wherein 0 < a < 10, 0 ≤ b < 10, 0 ≤ c < 10, and M1 and M2 are different and independently selected from Y, Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W or Sr;

[0009] The reinforcing layer comprises a chemical formula of C. j N k Carbon nitride, where 0 < j < 5, 0 < k < 5.

[0010] In some embodiments of this application, the reinforcing layer in the core-shell structured cathode material has a porous structure.

[0011] In some embodiments of this application, the ternary cathode material in the core-shell structure is selected from one or two of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0012] In some embodiments of this application, the particle size of the core in the core-shell structured cathode material is 4 μm to 15 μm;

[0013] The thickness of the electrolyte layer is 5 nm to 50 nm;

[0014] The thickness of the reinforcement layer is 5nm to 100nm.

[0015] In some embodiments of this application, the core-shell structured cathode material has one or more of the following characteristics:

[0016] (1) The total thickness of the outer coating layer is 10 nm to 100 nm;

[0017] (2)0<a<5, 0<b<5, 1<c<5;

[0018] (3) M1 and M2 are different and are each independently selected from Y, Co, Zr, Bi, La, Al, Ti or W;

[0019] (4) 0 < j < 3, 0 < k < 4.

[0020] A second aspect of this application provides a method for preparing a core-shell structured cathode material, comprising the following steps:

[0021] The core material, phosphate, and water are mixed and dispersed to prepare the base solution;

[0022] A metal salt solution is added to the base liquid and mixed to obtain a precipitate. The precipitate is then dried to obtain a pre-coated powder.

[0023] The pre-coated powder, lithium salt, carbon source and nitrogen source are mixed and heated at 200℃~800℃ to obtain a core-shell structured cathode material.

[0024] The core-shell structured cathode material includes a core and an outer coating layer. From the core outwards, the outer coating layer sequentially includes an electrolyte layer and a reinforcement layer.

[0025] The core material includes ternary cathode material;

[0026] The electrolyte layer comprises Li a M1 b M2 c Metal phosphates of (PO4)3, wherein 0 < a < 10, 0 ≤ b < 10, 0 ≤ c < 10, M1 and M2 are different and are selected from Y, Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W or Sr respectively;

[0027] The reinforcing layer comprises a chemical formula of C. j N k Carbon nitride, where 0 < j < 5, 0 < k < 5.

[0028] In some embodiments of this application, in the preparation method, the mass ratio of the core material to the phosphate is (1000-100):1;

[0029] The metal salt solution includes M1 salt and M2 salt; the mass ratio of the core material, the M1 salt, and the M2 salt is 1:(0.0001~0.01):(0.001~0.01);

[0030] The mass ratio of the core material to the nitrogen source is 1:(0.0005~0.5).

[0031] In some embodiments of this application, in the preparation method, the molar concentration of phosphate in the substrate is 0.001–0.1 mol / L;

[0032] The total molar concentration of metal cations in the metal salt solution is 0.001–0.1 mol / L.

[0033] In some embodiments of this application, the preparation method has one or more of the following features:

[0034] (1) The phosphate includes one or more of the following: ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate;

[0035] (2) The lithium salt includes one or more of lithium carbonate, lithium hydroxide and lithium acetate;

[0036] (3) The nitrogen source includes one or more of urea, uric acid and ammonium fluoride;

[0037] (4) The carbon source is selected from one or more of urea, uric acid and glucose, caramel and asphalt.

[0038] A third aspect of this application provides a battery positive electrode, wherein the active material of the battery positive electrode is a core-shell structure positive electrode material provided in the first aspect of this application, or a core-shell structure positive electrode material prepared by the preparation method provided in the second aspect of this application.

[0039] A fourth aspect of this application provides a secondary battery, including the battery positive electrode provided in the third aspect of this application, as well as a separator, a negative electrode, and an electrolyte.

[0040] A fifth aspect of this application provides an electrical device including the secondary battery provided in the fourth aspect of this application.

[0041] This application describes a method for coating an outer coating layer onto a ternary cathode material core. From the core outwards, the outer coating layer sequentially includes an electrolyte layer (mainly composed of metal phosphate salts) and a reinforcing layer (mainly composed of carbon nitride), thus creating a multi-layered coated composite electrode material. The electrolyte layer has a dense structure, which can suppress the dissolution of transition metals, while the reinforcing layer is porous and loose, which can effectively increase the compatibility between the interface and the electrolyte, and increase the wetting effect of the electrode, thereby improving the cycle stability and rate performance of the battery.

[0042] The core-shell structured cathode material of this application can, on the one hand, form an effective and stable electrode / electrolyte interface, reduce material interface corrosion and structural damage, reduce DCR growth, and improve the cycle and rate performance of the battery. On the other hand, it can effectively isolate the electrode material from direct contact with the electrolyte, significantly improve interface defects caused by HF corrosion, and can also increase the first discharge capacity of the battery to a certain extent.

[0043] The core-shell structured cathode material of this application has a simple preparation method, is easy to scale up, has high coating strength, can remain intact during electrode rolling, and effectively prevents excessive metal dissolution. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the core-shell structure of the cathode material in one embodiment of this application;

[0046] Figure 2 This is a flowchart illustrating the preparation process of a core-shell structured cathode material in one embodiment of this application.

[0047] Figure 3 This is a transmission microscope (TEM) image of Embodiment 1 of this application;

[0048] Figure 4 The energy dispersive spectroscopy (EDS) spectrum of the material prepared in Example 1 of this application is shown.

[0049] Figure 5 A comparison image of scanning electron microscope (SEM) images of the materials prepared in Comparative Example 1 and Example 1 of this application;

[0050] Figure 6 Comparison diagrams of X-ray diffraction (XRD) patterns of the materials prepared in Comparative Example 1 and Examples 1-2 of this application;

[0051] Figure 7 This is a comparison chart of the cycling performance of the materials prepared in Examples 1-2 and Comparative Examples 1-2 of this application at 25°C.

[0052] Figure 8 This is a comparison chart of the rate performance of the materials prepared in Examples 1-2 and Comparative Examples 1-2 of this application. Detailed Implementation

[0053] The present application is further described below with reference to the embodiments, examples, and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Furthermore, it should be understood that after reading the teachings of this application, those skilled in the art can make various alterations or modifications to the application, and these equivalent forms also fall within the protection scope of the appended claims.

[0054] 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 application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0055] the term

[0056] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0057] In this document, terms such as "preferred," "better," and "more preferred" are merely descriptions of implementation methods or examples that achieve better results, and should be understood as not constituting a limitation on the scope of protection of this application.

[0058] 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.

[0059] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," and "fifth 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," "fourth," and "fifth" etc. serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0060] 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.

[0061] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, optional 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. 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.

[0062] 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℃.

[0063] In this application, weight can be a well-known unit of mass in the chemical industry, such as μg, mg, g, or kg.

[0064] In this application, unless otherwise specified, molecular weight refers to average molecular weight, and further, unless otherwise specified, refers to weight-average molecular weight.

[0065] In a first aspect of this application, a core-shell structured cathode material is provided, comprising a ternary cathode material core, and an electrolyte layer (mainly composed of metal phosphate) and a reinforcing layer (mainly composed of carbon nitride) sequentially coated on the core. The electrolyte layer has a dense structure, which can suppress the dissolution of transition metals, and the reinforcing layer is porous and loose, which can effectively increase the compatibility between the interface and the electrolyte, and increase the wetting effect of the electrode, so that the material has high cycle and rate performance.

[0066] In this document, unless otherwise specified, "main component" refers to the component that mainly comprises the listed components, such as those with a mass content greater than 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99%. In some embodiments, "main component" may refer to a mass content of 100%. It should be understood that other components are permitted, such as unavoidable impurities, compositional variations due to the preparation method, and transition regions formed due to the contact and penetration of adjacent structural layers. By referring to the examples of the preparation method provided in the third aspect of this application, those skilled in the art can clearly understand the distribution and connection of the structural layers, as well as the meaning of "main component."

[0067] The core-shell structured cathode material of this application includes a core and an outer coating layer. From the core outwards, the outer coating layer sequentially includes an electrolyte layer and a reinforcing layer. "Sequentially includes" only indicates the order of positions and does not limit whether the related structural layers are in direct contact. For example, other functional layers, such as a fixing layer, can be further coated between the electrolyte layer and the reinforcing layer to improve the bonding force between the electrolyte layer and the reinforcing layer.

[0068] Figure 1 This is a schematic diagram of the core-shell structure of the cathode material in one embodiment of this application, including a core 100 and an electrolyte layer 210 and a reinforcing layer 220 sequentially coated outwards from the core. The electrolyte layer 210 and the reinforcing layer 220 together constitute the outer coating layer 200. The electrolyte layer has good density, which can effectively isolate the electrode / electrolyte interface and inhibit HF corrosion of the interface. On the other hand, the electrolyte layer can provide high conductivity, improving the rate performance of the material. The reinforcing layer has a relatively loose structure, which increases the compatibility between the electrode and the electrolyte. The electrolyte retention of the electrode is improved by about 15% compared with traditional coating materials.

[0069] In some embodiments, the core material is selected from one or both of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. For example, lithium nickel cobalt manganese oxide is specifically the compound LiNi. x Co y Mn1-x-y O2, 0 < x < 1, 0 < y < 1.

[0070] In some embodiments, the electrolyte layer comprises Li a M1 b M2 c Metal phosphate of (PO4)3. Further, 0 < a < 10, 0 ≤ b < 10, 0 ≤ c < 10, and even further, 0 < a < 5, 0 < b < 5, 1 < c < 5.

[0071] In some embodiments, M1 and M2 are different and independently selected from Y, Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W, or Sr. Further, M1 and M2 are different and independently selected from Y, Co, Zr, Bi, La, Al, Ti, and W.

[0072] In some embodiments, the reinforcing layer comprises a chemical formula of C j N k For carbon nitride, further, 0 < j < 5, 0 < k < 5. Even further, 0 < j < 3, 0 < k < 4.

[0073] In this application, the core of the core-shell structured cathode material has a suitable particle size. If the particle size of the core is too small, the energy density of the cell will be too low; if the particle size is too large, the electrode compaction will be too low. In some embodiments, the particle size of the core is 4 μm to 15 μm. For example, the particle size can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, etc.

[0074] In this application, unless otherwise specified, the terms "size," "particle size," and "diameter" generally refer to average values. In this application, "particle size" and "particle diameter" have the same definition, both representing the average particle size of spheres or spheroids.

[0075] The core-shell structured cathode material of this application has an outer coating layer with a suitable thickness, which is beneficial for achieving optimal electrochemical performance. This effectively avoids the inability to isolate the electrode / electrolyte interface reaction due to an excessively thin coating layer (e.g., 4 nm), or the instability of the phase interface due to an excessively thick coating layer (e.g., 60 nm).

[0076] In some embodiments, the thickness of the outer coating layer is 5nm to 50nm. For example, the thickness can be 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, etc. Other values ​​within the above range can be selected, and will not be described in detail here.

[0077] Furthermore, the thickness of the electrolyte layer is 5 nm to 50 nm.

[0078] Furthermore, the thickness of the reinforcement layer is 5nm to 50nm.

[0079] In some embodiments, the mass ratio of the outer coating layer to the core of the core-shell structured cathode material is preferably 1:(100 to 1000).

[0080] Second aspect of this application

[0081] In a second aspect of this application, a method for preparing a core-shell structured cathode material is provided, which is simple to operate and easy to scale up for production.

[0082] This application employs a suitable method (in-situ coating technology) to coat an outer coating layer onto a core (mainly composed of ternary cathode material). The outer coating layer exhibits high coating strength and remains intact during electrode rolling. From the core outwards, the outer coating layer comprises at least a dense electrolyte layer (mainly composed of metal phosphate) and a porous reinforcing layer (mainly composed of carbon nitride). The phosphate (Li) in the electrolyte layer... a M b N c (PO4)3) is electrochemically active and can undergo Li₂ oxidation during the first cycle. + Ion desorption and exchange increase the initial discharge capacity to a certain extent. The porous and loose reinforcement layer can effectively increase the compatibility between the interface and the electrolyte, and increase the wetting effect of the electrode, thereby effectively improving the cycle and rate performance of the material.

[0083] In some embodiments of this application, the preparation method of the core-shell structured cathode material includes the following steps:

[0084] S100: Mix and disperse the core material, phosphate, and water to prepare the base solution;

[0085] S200: Add a metal salt solution to the bottom liquid and mix to obtain a precipitate. Dry the precipitate to obtain a pre-coated powder.

[0086] S300: Pre-coated powder, lithium salt, carbon source and nitrogen source are mixed and heated at 200℃~800℃ to obtain a core-shell structured cathode material.

[0087] In the above preparation process, in step S100, the core material is dispersed in an environment containing a large amount of phosphate ions. Then, in step S200, the cations of metals M1 and M2 are introduced, causing the phosphate ions to precipitate and form a phosphate layer on top of the core material, resulting in a pre-coated powder. Then, in step S300, the pre-coated powder, lithium salt, carbon source, and nitrogen source are mixed and heated at a suitable temperature, thereby introducing lithium metal into the phosphate layer from step S200, resulting in a dense electrolyte layer. Simultaneously, the carbon source and nitrogen source form a porous reinforcing layer on the surface of the electrolyte layer. For a more detailed preparation process, please refer to [link to relevant documentation]. Figure 2 .

[0088] S100 preparation of base solution:

[0089] In this application, in step S100, the core material (ternary cathode material) is dispersed in an environment where a large amount of phosphate ions are present to obtain a base solution.

[0090] In some embodiments, the mass ratio of the core material to the phosphate is (1000-100):1.

[0091] The core material may be purchased or prepared using conventional methods known to those skilled in the art.

[0092] Optionally, the core material can be nickel cobalt manganese oxide, in which case the lithium salt in step S300 serves as a lithium source and a substrate for preparing the ternary cathode material; the core material can be lithium nickel cobalt manganese oxide, in which case the lithium salt (lithium supplementation lithium salt) in step S300 serves as a lithium supplementation.

[0093] During the formation process of lithium-ion batteries, the formation of the SEI film on the negative electrode consumes a large amount of active lithium, especially when high-capacity silicon-based negative electrode materials are added, resulting in low coulombic efficiency and battery capacity in the first week. Replenishing active lithium is an effective way to solve this problem. Positive electrode lithium replenishment involves adding lithium-containing compounds with high irreversible capacity to the positive electrode of a lithium-ion battery. Depending on the type of compound, they can be divided into binary lithium-containing compounds represented by Li₂O, Li₂O₂, and Li₂S; ternary lithium-containing compounds represented by Li₆CoO₄ and Li₅FeO₄; and organic lithium-containing compounds represented by Li₂DHBN and Li₂C₂O₄.

[0094] As an example, the core material (lithium nickel cobalt manganese oxide) can be prepared by including the following steps: preparing a precursor (nickel cobalt manganese oxide, Ni...) x Co y Mn 1-x-y(OH)₂ (0 < x < 1, 0 < y < 1) is mixed uniformly with a lithium source and heated in an atmosphere of oxygen and / or air. The heating temperature can be from 400℃ to 1000℃, for example, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, or 1000℃. The heating time can be from 8 to 30 hours. For example, the heating time can be 8 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, or 30 hours. Other values ​​within the above range are also acceptable and will not be elaborated further here.

[0095] In some embodiments, the core material is pulverized to a particle size of 4 μm to 15 μm before the phosphate is added and mixed with water.

[0096] In some embodiments, phosphate is added and mixed with water, dispersed, and then the pH is adjusted to 4-9. This is because in step S200, phosphate and metal cations undergo a precipitation reaction near pH=7 to generate M. x (PO4) y N m (PO4) n Composite in-situ coating material. Optionally, acetic acid or ammonia can be added to adjust the pH to 4–9. Further, the concentration of acetic acid or ammonia can be 0.08–0.12 mol / L.

[0097] In some embodiments, the molar concentration of phosphate in the substrate is 0.001–0.1 mol / L.

[0098] In some embodiments, the phosphate is selected from one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.

[0099] S200 preparation of pre-coated powder:

[0100] In this application, metal cations (M1 and M2 cations) are introduced in step S200, and they react with phosphate ions in the bottom solution obtained in step S100 to form a phosphate layer on the core material, thus obtaining a pre-coated powder.

[0101] In some embodiments, a metal salt solution is added to the base liquid and mixed to obtain a precipitate, which is then dried to prepare a pre-coated powder.

[0102] In some embodiments, the metal salt solution includes M1 salt and M2 salt, and further, the mass ratio of the core material, M1 salt and M2 salt is 1:(0.0001~0.01):(0.001~0.01).

[0103] In some embodiments, the total molar concentration of metal cations in the metal salt solution is 0.001 to 0.1 mol / L.

[0104] In some embodiments, the metal salt solution can be prepared according to conventional methods well known to those skilled in the art, by dissolving soluble M1 and M2 salts in water. After complete dissolution, the solution is allowed to stand for 12 to 20 hours, preferably more than 12 hours, to ensure uniform dispersion of the M1 and M2 elements in the aqueous solution. In some embodiments, M1 and M2 are different and independently selected from Ni, Co, Mn, Zr, Bi, Zn, La, Al, Ti, Ge, W, and Sr. Further, M1 and M2 are different and independently selected from Y, Co, Zr, Bi, La, Al, Ti, or W. Optionally, the metal salt solution can be one or more of chloride, sulfate, and oxalate solutions.

[0105] In this application, in step S200, a metal salt solution can be added to the base solution using methods well known to those skilled in the art. In some embodiments, the addition method includes: continuously conveying the solution to the base solution at a certain rate using a peristaltic pump to effectively control the rate at which elements M1 and M2 are introduced into the base solution and to control the thickness of the coating layer. Further, the addition rate can be 0.4 mL / min to 0.6 mL / min, more preferably 0.5 mL / min. Examples of addition rates include 0.4 mL / min, 0.45 mL / min, 0.5 mL / min, 0.55 mL / min, or 0.6 mL / min, etc. Other values ​​within the above range are also acceptable and will not be elaborated upon here.

[0106] In this application, there are no special restrictions on the method of drying the precipitate in step S200. It can be dried at 80°C in a rotary evaporator. Furthermore, the drying time can be 4h to 6h.

[0107] S300 is used to prepare core-shell structured cathode materials:

[0108] In step S300, the pre-coated powder obtained in step S200, lithium salt, carbon source, and nitrogen source are mixed and heated at a suitable temperature. The lithium salt and the phosphate of the pre-coated powder (M1) are then reacted. b M2 c (PO4)3) reacts to produce lithium-containing metal phosphate (Li) a M1 b M2 c (PO4)3) has high electrical conductivity, which can significantly improve the electrochemical performance of the material. Simultaneously, the carbon and nitrogen sources form a porous and loosely structured reinforcing layer on the surface of the electrolyte layer. In some embodiments, the lithium salt also acts as a lithium replenisher, reacting with the components of the core; the specific principle of lithium replenishment can be found in step S100.

[0109] Alternatively, the lithium salt may be one or more of lithium carbonate, lithium hydroxide, and lithium acetate. In this application, "more than" refers to two or more types.

[0110] Alternatively, the nitrogen source may be one or more of urea, uric acid, and ammonium fluoride.

[0111] Alternatively, the carbon source may be one or more of urea, uric acid and glucose, caramel and pitch.

[0112] In some embodiments, in step S300, the carbon source and the nitrogen source can be the same compound, which provides both carbon and nitrogen elements in step S300.

[0113] In some embodiments, the mass ratio of the core material to the nitrogen source is 1:(0.0005 to 0.5).

[0114] In some embodiments, the mass of the lithium salt added in step S300 is 0.1% to 10% of the mass of the core material in step S100.

[0115] In some embodiments, the heating temperature in step S300 can be between 200°C and 800°C. For example, the heating temperature can be 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, or 800°C. The heating time can be between 5 hours and 30 hours. For example, the heating time can be 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, or 30 hours.

[0116] A third aspect of this application provides a battery cathode, wherein the active component of the cathode is a core-shell structure cathode material provided in the first aspect of this application, or a core-shell structure cathode material prepared by the preparation method provided in the second aspect of this application.

[0117] A fourth aspect of this application provides a secondary battery, including the positive electrode provided in the third aspect of this application, as well as a separator, a negative electrode, and an electrolyte. The secondary battery of this application exhibits superior rate performance and cycle stability. In some embodiments, compared to coating materials prepared by conventional solid-state methods, the secondary battery prepared using the materials of this application shows an increase in specific capacity of ≥10%, an improvement in cycle performance of ≥10%, and an improvement in rate performance of ≥10%.

[0118] A fifth aspect of this application provides an electrical device including the secondary battery provided in the fourth aspect of this application.

[0119] The following are some specific examples.

[0120] The raw materials and reagents involved in the following specific embodiments can be obtained commercially or prepared by those skilled in the art using known methods.

[0121] 1. Preparation of core-shell structured cathode materials

[0122] Example 1

[0123] (1) Preparation of core material

[0124] The raw material metal oxide (Ni) 0.6 Co 0.1 Mn 0.3 (OH)₂ (purchased from Aladdin Reagent, particle size 4μm) was mixed with lithium hydroxide in a certain proportion to make the Li / (Ni+Mn) molar ratio of the mixture 1.04. The mixture was heated in a box furnace under oxygen atmosphere at 940℃ for 15 hours, and then pulverized by rollers (upper gap 15cm, lower gap 5cm) to obtain the chemical formula LiNi. 0.6 Co 0.1 Mn 0.3 O2 core material.

[0125] (2) Preparation of base liquid

[0126] Weigh out 50g of core material, add 1g of phosphate and 100mL of water and mix. Adjust the pH of the mixture to 6.1 with acetic acid, stir for 1 hour and let stand for 12 hours to obtain the bottom solution.

[0127] (3) Preparation of pre-coated powder

[0128] The metal salt solution was prepared by dissolving aluminum chloride (0.1151 g) and chlorinated peptide (0.2784 g) in deionized water (20 mL), stirring for 1 h, and then letting it stand for 12 h.

[0129] The prepared metal salt solution was transferred to the bottom liquid using a peristaltic pump at a rate of 0.5 mL / min to obtain a precipitate. The precipitate was then transferred to a rotary evaporator and dried at 80 °C for 5 h to obtain a pre-coated powder.

[0130] (4) Preparation of core-shell structured cathode material (LiNi) 0.6 Co 0.1 Mn 0.3 O2@Li 1.3 Al 0.3 Ti 1.7 (PO4)3&C3N4)

[0131] The pre-coated powder (20g), lithium salt (lithium hydroxide, 0.0933g), and urea (0.2g) were mixed and heated at 450°C for 20h under a protective gas atmosphere.

[0132] Example 2

[0133] Core-shell structured cathode material (LiNi) was prepared using a preparation method essentially the same as that used in Example 1. 0.6 Co 0.1 Mn 0.3 O2@Li 1.3 Al 0.3 Ge 1.7 The difference lies in the preparation of the base solution, which involves preparing the metal salt solution by dissolving aluminum chloride (0.1151 g) and germanium chloride (0.3658 g) in deionized water (20 mL), stirring for 1 h, and letting it stand for 12 h.

[0134] Example 3

[0135] Core-shell structured cathode material (LiNi) was prepared using a preparation method essentially the same as that used in Example 2. 0.65 Co 0.07 Mn 0.28 O2@Li 1.3 Y 0.3 Ge 1.7 The difference lies in the fact that the raw material metal oxide used in the core material preparation step is Ni (PO4)3 & C3N4. 0.60 Co 0.07 Mn 0.28 (OH)2 (purchased from Aladdin Reagent, particle size 4μm); In the step of preparing the base solution, the metal salt solution is prepared by the following steps: dissolve yttrium sulfate (0.2551g) and germanium acetate (0.3858g) in deionized water (20mL), stir for 1h, and let stand for 12h.

[0136] Comparative Example 1

[0137] This comparative example provides an unmodified ternary cathode material (LiN). i0.6 Co 0.1 Mn 0.3 O2), the specific steps are as follows:

[0138] The core material was prepared in exactly the same manner as in Example 1. The core material was sintered at 450°C for 15 hours in air.

[0139] Comparative Example 2

[0140] This comparative example provides a core-shell structured cathode material (LiNi) coated using a conventional dry coating method. 0.6 Co 0.1 Mn 0.3 The specific steps are as follows: (O2@Al2O3)

[0141] The core material was prepared in exactly the same manner as in Example 1. The core material (2.5 kg) was mixed evenly with nano-alumina (8 g) and sintered at 450 °C for 15 h in an air atmosphere in a box furnace.

[0142] Comparative Example 3

[0143] This comparative example provides a core-shell structured cathode material (LiNi) coated using a conventional dry coating method. 0.6 Co 0.1 Mn 0.3 The specific steps are as follows: (O2@TiO2)

[0144] The core material was prepared in exactly the same manner as in Example 1. The core material (2.5 kg) was mixed with nano-titanium dioxide (10 g) and sintered at 450 °C for 15 h in an air atmosphere in a box furnace.

[0145] Comparative Example 4

[0146] This comparative example provides a core-shell structured cathode material (LiNi) coated using a conventional dry coating method. 0.6 Co 0.1 Mn 0.3 The specific steps are as follows: (O2@GeO2)

[0147] The core material was prepared in exactly the same manner as in Example 1. The core material (2.5 kg) was mixed evenly with nano-germanium dioxide (10 g) and sintered at 450 °C for 15 h in an air atmosphere in a box furnace.

[0148] 2. Morphological testing

[0149] The cathode material (LiNi) prepared in Example 1 was analyzed using transmission electron microscopy (TEM). 0.6 Co 0.1 Mn 0.3 O2@Li 1.3 Al 0.3 Ti 1.7 Morphological characterization was performed using (PO4)3 & C3N4, and the resulting TEM images are shown in the attached figure. Figure 3 .from Figure 3 The presence of a double-layer coating structure can be observed, with a coating thickness of approximately 10 nm. Lattice comparison confirms that the outer coating is a nitrogen-containing graphite compound.

[0150] The cathode material prepared in Example 1 was characterized using an energy dispersive spectroscopy (EDS) instrument, and the resulting EDS image is shown in the attached figure. Figure 4 .according to Figure 4 It can be seen that elements such as Al, Ti, P, C, and N can be detected on the material surface, indicating that phosphates and carbon and nitrogen compounds have been successfully coated on the material surface.

[0151] The cathode materials (LiNi) prepared in Comparative Example 1 and Example 1 were analyzed using scanning electron microscopy. 0.6 Co 0.1 Mn 0.3 O2@Li 1.3 Al 0.3 Ti 1.7 Morphological characterization of (PO4)3 and C3N4 was performed separately, and the comparison of the obtained SEM images is shown in the attached figure. Figure 5 .according to Figure 5 It can be seen that, compared with the uncoated cathode material, the material prepared in the example has a distinct coating layer structure on its surface. The outer layer of the coating layer is relatively loose, while the inner layer is a dense structure, resulting in a good overall coating effect.

[0152] 3. Structural Feature Characterization

[0153] First, the positive electrode active materials prepared in each example and comparative example were cyclically subjected to a voltage of 2.8V-4.4V and a scaling factor of 0.1C / 0.1C for 50 cycles. Then, the cyclic positive electrode active material powder was placed in the sample stage of an XRD testing instrument (model Bruker D8), and X-ray diffraction (XRD) patterns were obtained using a scanning rate of 1° / min and a scanning angle range of 10° to 80°. The XRD comparison results are attached. Figure 6 .

[0154] According to the appendix Figure 6 As can be seen, compared with Comparative Example 1, no impurity peaks appeared in the sample of the embodiment after 100 cycles, indicating that the coating did not change the crystal structure of the positive electrode active material, and the material structure has good stability and no structural changes occurred.

[0155] The above XRD data was processed using the Rietveld method to refine the XRD data, resulting in the refined data shown in Table 3-1 below.

[0156] Table 3-1

[0157]

[0158] According to the XRD refinement results in Table 3-1, the samples from Examples 1 and 2, after cycling, showed that... 003 / 104 The strength is greater than that of Comparative Example 1 because coating with phosphate and carbonitride compounds isolates the electrode / electrolyte contact, reduces HF corrosion of the material, and also inhibits the resulting surface lattice reconstruction, which helps to reduce Li. + / Ni 2+The increased mixing degree makes the layered structure of the material more ordered and complete, thereby improving the structural stability of the positive electrode active material. In addition, the values ​​of the cell parameters c, a, c / a and cell volume all increase. This is because the coated P atoms can form chemical bonds with the Ni on the material surface, stabilizing the Ni on the surface in the fully charged state. 4+ This further enhances the stability of the positive electrode active material structure.

[0159] 4. Performance Testing

[0160] 4.1. High and low temperature cycling and rate performance testing

[0161] The materials prepared in the examples and comparative examples were subjected to cycling and rate performance tests at 25°C and 45°C, respectively. The test methods are as follows: appropriate amounts of the materials prepared in the examples and comparative examples were weighed and assembled into coin cells, wherein the electrode material: conductive carbon black = 90:10wt%, the solvent was NMP, and the cell electrode surface density was 1.2 mg / cm³. 2 At a voltage of 2.8-4.4V and a temperature of 25℃, after one charge-discharge cycle at a rate of 0.1C / 0.1C, the cells were charged and discharged at rates of 0.1C / 1C, 0.2C / 1C, 0.5C / 1C, and 1C / 1C. Then, a cycle performance test (50 cycles) was conducted at a rate of 1C / 1C at 25℃ and 45℃. The test results are shown in Table 4-1 below.

[0162] Table 4-1

[0163]

[0164] As shown in Table 4-1, the capacity and retention performance of Comparative Examples 2 to 4 are not significantly improved compared to Comparative Example 1. However, the data from the embodiments shows that the batteries made from the materials of this application exhibit a charge / discharge capacity increase of approximately 2-5 mAh / g compared to the comparative examples, a significant improvement in rate performance, and markedly enhanced cycle performance and rate performance at 45°C (see appendix for comparison results). Figure 7 and 8 This demonstrates that the structure of the material in the embodiments of this application can form an effective and stable interface layer, reducing the interface reaction between the electrode and the electrolyte. At the same time, the coating layer has high lithium-ion conductivity and lithium-ion storage function, which significantly improves the initial discharge capacity and rate performance of the material.

[0165] 4.2. Transition Metal Dissolution Test

[0166] Weigh appropriate amounts of the positive electrode materials prepared in the examples and comparative examples, and assemble them into coin cells. When the cells are fully charged (4.4V), they are stored at 60°C for 30 days and 60 days respectively. The cells are then disassembled, the positive electrode plates are cleaned with DMC, dried, and the active material layer of the positive electrode plates is scraped off. The active material layer is then dissolved in aqua regia by heating for 15-30 minutes. The solution is subjected to ICP testing to determine the content of Ni, Co, and Mn. The test results are shown in Table 2.

[0167] Table 4-2 Dissolution of Ni, Co, and Mn Metals

[0168]

[0169] As can be seen from the data in Table 4-2, the amount of metal leaching in the battery made from the material of this application embodiment after long-term storage is significantly lower than that of the comparative example. This indicates that the material of this application embodiment can resist HF corrosion, form an effective and stable interface layer, prevent transition metal ions from dissolving into the electrolyte, reduce the interface reaction between the electrode and the electrolyte, and improve the cycle performance of the battery.

[0170] All references to this application are incorporated herein by reference as if each document were individually incorporated herein by reference. Unless they conflict with the purpose and / or technical solution of this application, all cited references are incorporated herein by reference in their entirety and for all purposes. When references are cited in this application, the definitions of relevant technical features, terms, nouns, phrases, etc., are also incorporated herein by reference. Examples and preferred embodiments of the cited technical features may also be incorporated herein by reference, but only to the extent that they enable the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, this application shall prevail or modifications shall be made adaptably to the description in this application.

[0171] The technical features of the above-described embodiments and examples can be combined in any suitable manner. For the sake of brevity, not all possible combinations of the technical features in the above-described embodiments and examples 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.

[0172] The embodiments described above merely illustrate several implementation methods of this application and should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Furthermore, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to this application, and the equivalent forms obtained also fall within the protection scope of this application. It should also be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the protection scope of the appended claims. Therefore, the protection scope of this patent application 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 core-shell structured cathode material, characterized in that, The battery positive electrode comprises a core and an outer coating layer, the outer coating layer comprises an electrolyte layer and a reinforcing layer in sequence from the core outward; the electrolyte layer is dense in structure; and the reinforcing layer has a porous structure. The particle size of the core is 4-15 μm; the thickness of the electrolyte layer is 5-50 nm; the thickness of the reinforcing layer is 5-50 nm; and the total thickness of the outer coating layer is 10-100 nm. The material of the core comprises a ternary positive electrode material. The electrolyte layer comprises a metal phosphate of the formula Li 1.3 M1 0.3 M2 1.7 (PO4)3, M1 is selected from Y, M2 is selected from Ge; The reinforcing layer comprises carbon nitride of the formula C j N k where 0 < j < 5 and 0 < k < 5.

2. The core-shell structured cathode material of claim 1, wherein, The ternary positive electrode material is selected from one or both of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

3. A method for producing the core-shell structured cathode material according to any one of claims 1 to 2, characterized by, The method comprises the following steps: Mixing, dispersing and preparing a base solution by mixing the material of the core, a phosphate and water; Mixing a metal salt solution with the base solution to obtain a precipitate, drying the precipitate and preparing a pre-coated powder; Mixing the pre-coated powder, a lithium salt, a carbon source and a nitrogen source, and heating at 200-800 ℃ to prepare the core-shell structure positive electrode material.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the material of the core to the phosphate is (1000-100):1; The metal salt solution comprises M1 salt and M2 salt; and the mass ratio of the material of the core, the M1 salt and the M2 salt is 1:(0.0001-0.01):(0.001-0.01); The mass ratio of the material of the core to the nitrogen source is 1:(0.0005-0.5).

5. The preparation method according to claim 4, characterized in that, The molar concentration of phosphate in the base solution is 0.001-0.1 mol / L; The total molar concentration of metal cations in the metal salt solution is 0.001-0.1 mol / L.

6. The production method according to any one of claims 3 to 5, characterized by, The battery positive electrode has one or more of the following characteristics: (1) The phosphate comprises one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate and potassium dihydrogen phosphate; (2) The lithium salt comprises one or more of lithium carbonate, lithium hydroxide and lithium acetate; (3) The nitrogen source comprises one or more of urea, uric acid and ammonium fluoride; (4) The carbon source is selected from one or more of urea, uric acid, glucose, caramel and pitch.

7. A battery positive electrode, characterized by, The active material of the battery positive electrode is the core-shell structure positive electrode material prepared by the method of any one of claims 1-2, or the core-shell structure positive electrode material prepared by the method of any one of claims 3-6.

8. A secondary battery characterized by comprising: The battery positive electrode comprises the battery positive electrode of claim 7, a separator, a negative electrode and an electrolyte.

9. An electrical device, characterized by The secondary battery comprises the secondary battery of claim 8.

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