Positive electrode active material and preparation method therefor, positive electrode sheet, battery, battery pack, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, a battery pack, and an electric device. The positive electrode active material comprises a positive electrode active material matrix and a coating layer present on the surface of the positive electrode active material matrix; the coating layer comprises a Janus material; and the Janus material comprises a metal carbide and a metal oxide. In the positive electrode active material provided by the present invention, a Janus material is coated on the surface of a positive electrode active material matrix, and the Janus material comprises a metal carbide and a metal oxide, so that a Schottky junction can be formed on the surface of positive electrode active material particles, thereby generating an electric field that enables unidirectional electron transport, accelerating the transport of electrons, and thus improving the electronic conductivity of the positive electrode active material and enhancing the charging capacity and cycling performance of batteries.

Description

Positive electrode active materials and their preparation methods, positive electrode sheets, batteries, battery packs and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202510229833.3, filed on February 27, 2025, entitled "Positive Electrode Active Material and Preparation Method Thereof, Positive Electrode Sheet, Battery, Battery Pack and Electrical Device", the entire contents of which are incorporated herein by reference.

[0002] This application claims priority to Chinese Patent Application No. 202510380715.2, filed on March 26, 2025, entitled "Positive Electrode Active Material and Preparation Method Thereof, Positive Electrode Sheet, Battery, Battery Pack and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to a positive electrode active material and its preparation method, a positive electrode sheet, a battery, a battery pack, and an electrical device, belonging to the field of battery technology. Background Technology

[0004] The positive electrode active material in lithium-ion batteries is one of the key factors determining battery performance. With the rapid development of portable electronic devices, electric vehicles, and energy storage systems, the demand for high-performance batteries continues to grow. The choice of positive electrode active material directly affects the battery's energy density, power density, cycle life, safety, and cost, thus becoming a focus of lithium-ion battery research and development.

[0005] The existing cathode active materials still suffer from low electronic conductivity, which affects the battery's charging capacity and cycle performance, thus becoming a technical problem that urgently needs to be solved at this stage. Summary of the Invention

[0006] The main objective of this application is to provide a positive electrode active material with high electronic conductivity, which can improve the charging capacity and cycle performance of the battery.

[0007] This application also provides a method for preparing a positive electrode active material, which can prepare the above-mentioned positive electrode active material, and the process is simple and low in cost.

[0008] This application also provides a positive electrode sheet comprising the above-mentioned positive electrode active material. Therefore, when this positive electrode sheet is applied to a battery, it can improve the battery's charging capacity and cycle performance.

[0009] This application also provides a battery including the above-mentioned positive electrode, thus the battery has a high charging capacity and excellent cycle performance.

[0010] This application also provides a battery pack including the above-mentioned battery, thus the battery pack has a high charging capacity and excellent cycle performance.

[0011] This application also provides an electrical device including the aforementioned battery or battery pack, thus the battery performance of the electrical device is superior.

[0012] In a first aspect, this application provides a positive electrode active material, including a positive electrode active material matrix and a coating layer present on the surface of the positive electrode active material matrix;

[0013] The coating layer comprises a janus material; the janus material comprises metal carbides and metal oxides.

[0014] The positive electrode active material described above is obtained by partially oxidizing the metal carbide.

[0015] In the positive electrode active material described above, the molar ratio of the metal carbide to the metal oxide is 1:(0.8-1.2).

[0016] The positive electrode active material as described above, wherein the metal element in the metal carbide and / or the metal oxide includes at least one of Ti, Co, Nb, Fe, Ni and Mo.

[0017] As described above, the thickness of the coating layer in the positive electrode active material is 50nm-200nm.

[0018] The positive electrode active material described above has a Dv50 of 1 μm to 1.5 μm.

[0019] In the positive electrode active material described above, the Janus material accounts for 1%-5% of the mass percentage of the positive electrode active material matrix, preferably 1.2%-2.6%.

[0020] The positive electrode active material as described above, wherein the positive electrode active material matrix includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials.

[0021] Secondly, this application provides a method for preparing the positive electrode active material as described above, comprising the following steps:

[0022] 1) The metal carbide is subjected to hydrothermal treatment to obtain Janus material;

[0023] 2) The raw material system including the Janus material and the positive electrode active material matrix is ​​subjected to heat treatment to obtain the positive electrode active material.

[0024] In the preparation method described above, the temperature of the hydrothermal treatment is 140℃-180℃, preferably 145℃-160℃;

[0025] And / or, the hydrothermal treatment time is 12h-16h, preferably 13h-14h.

[0026] In the preparation method described above, the heat treatment temperature is 100℃-150℃, preferably 115℃-120℃.

[0027] Thirdly, this application provides a positive electrode sheet, including a positive electrode active layer, wherein the positive electrode active layer comprises the positive electrode active material as described above or the positive electrode active material prepared by the preparation method as described above.

[0028] Fourthly, this application provides a battery including the positive electrode as described above.

[0029] Fifthly, this application provides a battery pack including the battery as described above.

[0030] Sixthly, this application provides an electrical device including a battery as described above or a battery pack as described above.

[0031] The positive electrode active material provided in this application, by coating the surface of the positive electrode active material matrix with Janus material, which includes metal carbides and metal oxides, can form a Schottky junction on the surface of the positive electrode active material particles, thereby forming an electric field for unidirectional electron movement, accelerating the electron movement rate, thereby improving the electronic conductivity of the positive electrode active material, and enhancing the charging capacity and cycle performance of the battery. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments of this application or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 is a schematic diagram of the structure of the positive electrode active material in Embodiment 1 of this application;

[0034] Figure 2 is a schematic diagram of the structure of the positive electrode active material of Comparative Example 4 of this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] The positive electrode active material in a lithium-ion battery largely determines the overall performance of the battery. However, many existing positive electrode active materials generally suffer from low electronic conductivity. This characteristic limits the ability of lithium ions to rapidly insert and extract during charging and discharging, thus affecting the battery's charging capacity and cycle performance.

[0037] To overcome these limitations, researchers have explored various methods to improve the conductivity of cathode active materials. Metal doping and carbon coating are among the most common strategies. Carbon coating enhances electronic conductivity by forming a conductive carbon layer on the surface of cathode active material particles. However, due to the limitations of the calcination temperature of the cathode active material, the graphitization degree of the carbon source is typically low, resulting in limited improvement in conductivity. Furthermore, existing methods attempting to improve electronic conductivity by constructing Schottky junctions also have shortcomings. These methods usually rely on the mixing of conductor and semiconductor materials, but the disordered electron conduction direction in the mixture prevents the full utilization of the advantages of Schottky junctions. Additionally, while constructing semiconductor structures using nitrogen-doped carbon can improve electronic conductivity to some extent, the limited amount of nitrogen doping restricts the formation of Schottky junctions and introduces a degree of disorder. This method may exhibit different effects during charging and discharging, failing to simultaneously achieve both.

[0038] The inventors of this application have discovered through research that accelerating the directional movement of electrons by forming an ordered, directional electric field can significantly improve the electrical conductivity of positive electrode active materials.

[0039] Based on this, in a first aspect, this application provides a positive electrode active material, including a positive electrode active material matrix and a coating layer present on the surface of the positive electrode active material matrix; the coating layer includes a Janus material; the Janus material includes metal carbides and metal oxides.

[0040] It is understood that Janus materials are a class of materials with asymmetric structures, exhibiting two different or opposite chemical or physical properties within the same particle, lamellar, or fiber. The Janus materials of this application include metal carbides and metal oxides, meaning that a portion of the same particle in this material is a metal carbide, and another portion is a metal oxide, with a defined interface, exhibiting different chemical or physical properties in different regions of the same particle.

[0041] This application improves the electronic conductivity of the positive electrode active material by coating the surface of the positive electrode active material matrix with a Janus material, which includes metal carbides and metal oxides, thereby enhancing the battery's charging capacity and cycle performance. This is because the unique structure of the Janus material allows the formation of a Schottky junction on the surface of the positive electrode active material particles—the interface between a semiconductor and a conductor. In this case, the metal carbide provides conductive properties, while the metal oxide provides semiconductor properties. A Schottky junction refers to the bending of the semiconductor's energy bands at the interface when a conductor and semiconductor come into contact, forming a Schottky barrier and creating an electric field that allows electrons to move in one direction. Specifically, within the particle, an electric field can be formed that moves directionally from the metal oxide to the metal carbide, driving more efficient electron transport, accelerating electron mobility, and improving electronic conductivity. Therefore, the positive electrode active material of this application exhibits both conductive and semiconductor properties within the same particle, and a directional electric field can be formed within the particle itself. Furthermore, during charging and discharging, electrons can find suitable paths and form directional electric fields, which facilitates accelerated directional electron movement, thereby improving the bulk electronic conductivity of the positive electrode active material. Furthermore, the abundant conductive network between particles can reduce interfacial resistance and increase the contact area between the active particles and the electrolyte, thereby providing more channels and reaction sites for lithium-ion insertion and extraction, which is beneficial for improving specific capacity. In addition, during charge and discharge, the metal oxides in the Janus material provide additional stability, preventing structural damage caused by material expansion and contraction during charge-discharge cycles, and to some extent protecting the positive electrode active material from electrolyte corrosion, which helps extend the battery's cycle life. Simultaneously, it can also improve the conductivity of the positive electrode active material and the battery's rate performance.

[0042] Therefore, the positive electrode active material provided in this application, by coating the surface of the positive electrode active material matrix with Janus material, which includes metal carbides and metal oxides, can form a Schottky junction on the surface of the positive electrode active material particles, thereby forming an electric field for unidirectional electron movement, accelerating the electron movement rate, thereby improving the electronic conductivity of the positive electrode active material, and enhancing the charging capacity and cycle performance of the battery.

[0043] In some embodiments of this application, the janus material is obtained by partially oxidizing a metal carbide.

[0044] The Janus material of this application is formed by partially oxidizing metal carbides to create a Janus material that simultaneously possesses the properties of both metal oxides and metal carbides. This material exhibits both conductor and semiconductor characteristics, enabling the formation of Schottky junctions on the surface of positive electrode active material particles. This creates an electric field that allows electrons to move in one direction, accelerating the electron mobility and thereby improving the electronic conductivity of the positive electrode active material, as well as enhancing the battery's charging capacity and cycle performance.

[0045] In some embodiments of this application, the molar ratio of metal carbide to metal oxide is 1:(0.8-1.2), for example, it can be a range consisting of 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2 or any two of them.

[0046] In this application, the molar ratio of metal carbide to metal oxide is within the aforementioned range, providing effective conductor and semiconductor properties, and an effective directional electric field can be formed within the particles themselves. Furthermore, during charging and discharging, electrons can find suitable paths and form directional electric fields, which facilitates accelerated directional electron movement, thereby improving the electronic conductivity of the positive electrode active material, and consequently enhancing the battery's charging capacity and cycle performance.

[0047] In some embodiments of this application, the metal element in the metal carbide and / or metal oxide includes at least one of Ti, Co, Nb, Fe, Ni and Mo.

[0048] The metal elements in the metal carbides and / or metal oxides of this application include the types mentioned above. The carbides or oxides formed by these metal elements can effectively form a Schottky junction at the interface between the semiconductor and the conductor, thereby forming an electric field that allows electrons to move in one direction, accelerating the electron movement rate, thereby improving the electronic conductivity of the positive electrode active material, and enhancing the charging capacity and cycle performance of the battery.

[0049] In some embodiments of this application, the thickness of the coating layer is 50nm-200nm, for example, it can be a range of 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm or any two of these.

[0050] The thickness of the coating layer in this application, within the aforementioned range, effectively creates an electric field that facilitates unidirectional electron movement, accelerating electron mobility and thereby improving the electronic conductivity of the positive electrode active material, as well as enhancing the battery's charging capacity and cycle performance. Furthermore, the suitable thickness range is sufficient to form a continuous and uniform conductive network, significantly improving the electronic conductivity of the positive electrode active material without excessively increasing its resistance. It also does not significantly hinder the diffusion path of lithium ions, ensuring efficient ion transport and thus improving the battery's rate performance.

[0051] This application does not limit the testing method for the thickness of the coating layer. For example, the positive electrode active material can be coated on aluminum foil, and then a cross-section can be obtained by a shearing machine. A scanning electron microscope can be used to take a picture, and the thickness of more than 10 uniformly coated positions can be measured using a ruler. The average value can be taken to obtain the thickness of the coating layer.

[0052] In some embodiments of this application, the Dv50 of the positive electrode active material is 1 μm-1.5 μm, for example, it can be a range of 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or any two of these.

[0053] The Dv50 of the positive electrode active material in this application is within the aforementioned range, which is beneficial for forming a uniform conductive network in the electrode, ensuring rapid electron and ion transport, and improving the overall conductivity and energy density of the battery. Furthermore, a suitable Dv50 results in less mechanical stress due to volume changes during charge and discharge, thereby reducing material pulverization and structural damage, and enhancing cycle stability.

[0054] This application does not limit the test method for Dv50 of positive electrode active material. For example, the positive electrode active material can be dispersed in anhydrous ethanol, sonicated for 5 minutes, and then measured using a laser particle size analyzer.

[0055] In some embodiments of this application, the janus material accounts for 1%-5% of the mass percentage of the positive electrode active material matrix, for example, it can be a range of 1%, 1.2%, 1.5%, 2%, 2.6%, 3%, 3.5%, 4%, 4.5%, 5% or any two of these; preferably 1.2%-2.6%.

[0056] In this application, the mass percentage of Janus material in the positive electrode active material matrix is ​​within the above-mentioned range, which is beneficial to forming an electric field for unidirectional electron movement, accelerating the electron movement rate, thereby improving the electronic conductivity of the positive electrode active material, and enhancing the charging capacity and cycle performance of the battery.

[0057] Specifically, the positive electrode active material matrix may include at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials.

[0058] Secondly, this application provides a method for preparing the above-mentioned positive electrode active material, comprising the following steps:

[0059] 1) Hydrothermal treatment of metal carbides yields Janus material;

[0060] 2) The raw material system, including Janus material and positive electrode active material matrix, is subjected to heat treatment to obtain positive electrode active material.

[0061] The Janus material of this application is based on metal carbides, which are partially oxidized through hydrothermal oxidation to form a Janus structure that simultaneously possesses semiconductor and conductor properties, combining the properties of metal oxides and metal carbides. Specifically, 200mg-500mg of metal carbide powder is ultrasonically treated for 30-60min in a mixed solution of 0.5-1mol / L HCl and 0.1-0.6mol / L NaBF4 in 30-50mL. The solution is then transferred to a forced-air drying oven for hydrothermal treatment, followed by centrifugal drying to obtain the partially oxidized metal carbide powder, i.e., the Janus material, abbreviated as MO / MC, where M is a metal element, including at least one selected from Ti, Co, Nb, Fe, Ni, and Mo.

[0062] The MO / MC powder was then dispersed in deionized water and mixed with the positive electrode active material matrix. After heating, the mixture was sonicated to ensure uniform mixing and to coat the surface of the positive electrode active material matrix with the MO / MC powder. After centrifugation, the mixture was dried for at least 12 hours to obtain the positive electrode active material.

[0063] This application does not impose any particular restrictions on the preparation method of the positive electrode active material matrix, including but not limited to high-temperature solid-state method, sol-gel method, hydrothermal method, microwave synthesis method, co-precipitation method, etc. The impurity content, morphology, particle size and intrinsic electrochemical activity of the positive electrode active material synthesized by different methods will be different, but they will not have a significant impact on the coating effect of the Janus material in this application.

[0064] This application allows the use of ultrasonic instruments to fully disperse materials, including but not limited to ultrasonic processors, ultrasonic emulsifiers, ultrasonic stirrers, ultrasonic cleaners, and ultrasonic homogenizers.

[0065] This application utilizes a stirrer to achieve material dispersion and full reaction. Such devices include, but are not limited to, magnetic stirrers, frame stirrers, top-entry stirrers, side-entry stirrers, chemical stirrers, paddle stirrers, or circulating convection devices. Care should be taken to avoid introducing dust, impurities, or other moisture during the stirring process, which could alter the cleanliness of the system. The stirring speed can be 400 rpm to 1000 rpm.

[0066] The heating devices used in the heat treatment of this application include, but are not limited to, constant temperature heating tables, heating plates, electric heating plates, etc.

[0067] This application can be dried using a freeze dryer, wherein the freezing temperature can be -50℃ to -80℃ and the vacuum degree can be 10. -3 bar to 10 -6 bar.

[0068] The method for preparing the positive electrode active material provided in this application can prepare the positive electrode active material of the first aspect mentioned above, and the material has a high electronic conductivity, which can improve the charging capacity and cycle performance of the battery.

[0069] In some embodiments of this application, the temperature of the hydrothermal treatment is 140°C-180°C, for example, it can be a range of 140°C, 145°C, 150°C, 160°C, 170°C, 180°C or any two of them, preferably 145°C-160°C.

[0070] In some embodiments, the hydrothermal treatment time is 12h-16h, for example, it can be a range of 12h, 13h, 14h, 15h, 16h or any two of them, preferably 13h-14h.

[0071] The hydrothermal treatment temperature and time in this application are within the aforementioned range, which can effectively control the degree of oxidation of metal carbides, forming a composite structure of partially oxidized metal carbides, i.e., Janus material, thereby improving the material's electrical conductivity and stability. It can also improve the efficiency of the hydrothermal reaction, ensuring the reaction proceeds fully while avoiding excessive oxidation or structural damage caused by excessively high temperatures or prolonged treatment times.

[0072] In some embodiments of this application, the heat treatment temperature is 100℃-150℃, for example, it can be a range of 100℃, 110℃, 115℃, 120℃, 130℃, 140℃, 150℃ or any two of them, preferably 115℃-120℃.

[0073] The heat treatment temperature in this application is within the aforementioned range, which facilitates thorough mixing of the materials, prevents polymerization of the positive electrode active material matrix itself, and promotes the coating of MO / MC powder onto the surface of the positive electrode active material matrix. This improves the electronic conductivity of the positive electrode active material, thereby enhancing the battery's charging capacity and cycle performance.

[0074] Thirdly, this application provides a positive electrode sheet, including a positive electrode active layer, which includes the positive electrode active material as described above or the positive electrode active material prepared by the aforementioned preparation method.

[0075] The positive electrode sheet of this application can be prepared using conventional techniques in the art. Specifically, the above-mentioned positive electrode active material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a positive electrode active layer slurry. Then, the positive electrode active layer slurry is coated on at least one functional surface of the positive electrode current collector, and after drying, the positive electrode sheet of this application can be obtained.

[0076] This application does not specifically limit the type of positive current collector, which may include at least one of gasket, steel mesh, and nickel mesh.

[0077] This application does not specifically limit the categories of conductive agents and adhesives. The conductive agents, adhesives and other components can be selected from conventional substances in the field. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite and graphene, and the adhesive can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymers, polyimide, styrene-butadiene rubber and styrene-acrylic rubber.

[0078] This application does not specify the coating method; any coating method such as gravure coating, extrusion coating, spraying, or screen printing can be used to achieve the coating of the positive electrode active layer slurry.

[0079] The positive electrode sheet provided in this application includes the above-mentioned positive electrode active material. Therefore, when the positive electrode sheet is applied to a battery, it can improve the battery's charging capacity and cycle performance.

[0080] Fourthly, this application provides a battery including the aforementioned positive electrode, which has advantages corresponding to the aforementioned positive electrode, and will not be elaborated further.

[0081] In addition to the positive electrode, the battery of this application also includes a separator, a negative electrode, and an electrolyte. The composition of the negative electrode can refer to conventional negative electrode sheets in the art, for example, it can include at least one of graphite negative electrode, graphene negative electrode, and lithium metal negative electrode. The separator can also be a separator conventionally used in the art, such as PP film, PE film, etc.

[0082] The electrolytes involved in the assembly process include various series such as common lithium-ion primary battery electrolytes, lithium-ion secondary battery electrode solutions, lithium-sulfur battery electrolytes, and lithium-air battery electrolytes. Additionally, solid electrolytes (including but not limited to inorganic solid electrolytes such as sulfides, oxides, and phosphates, or polyethylene oxide electrolytes, two-phase polymer electrolytes, organic electrolytes, or inorganic / organic composite electrolytes) and semi-solid electrolytes (including but not limited to polyethylene oxide PEO-LiTFSI, vinylidene fluoride-hexafluoropropylene copolymer (P(VDF-HFP)), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and VC-PETEA crosslinked polymer electrolytes) can be selected based on the specific application and the positive electrode active material system. During actual battery assembly, the electrolyte dosage and overall proportion need to be considered, including but not limited to 1.6g / Ah-1.8g / Ah, and adjustments can be made as needed.

[0083] The battery of this application can be prepared using conventional methods in the art. Specifically, the positive electrode, separator and negative electrode can be stacked in sequence, and the cell can be obtained by stacking or winding. Then, the battery can be obtained by baking, liquid injection, formation and packaging.

[0084] Fifthly, this application provides a battery pack including the battery as described above, which has advantages corresponding to the above-mentioned positive electrode plate, and will not be repeated here.

[0085] Sixthly, this application provides an electrical device including the battery or battery pack as described above, which has advantages corresponding to the positive electrode plate mentioned above, and will not be elaborated further.

[0086] The electrical equipment used in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles), electronic equipment (e.g., computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (e.g., watches, wristbands, VR glasses, etc.), and household appliances (e.g., air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without any particular limitation.

[0087] The technical solution of this application will be further described below with reference to specific embodiments.

[0088] Example 1

[0089] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0090] 1) Sonicate 250 mg of titanium carbide powder in 30 mL of a mixed solution of 1 mol / L HCl and 0.1 mol / L NaBF4 for 45 min. Then transfer it to a forced-air drying oven and perform hydrothermal treatment at 150 °C for 13 h. After hydrothermal treatment, centrifuge and dry to obtain locally oxidized metal carbides, i.e., Janus material, which can be represented as TiO2 / Ti3C2.

[0091] 2) TiO2 / Ti3C2 powder was dispersed in deionized water and mixed with lithium iron phosphate powder (positive electrode active material matrix). The mass ratio of the positive electrode active material matrix to TiO2 / Ti3C2 powder was 1:0.012. The mixture was heated to 120℃ and then ultrasonicated. After homogenization, it was centrifuged and dried in a freeze dryer for more than 12 hours. After drying, TiO2 / Ti3C2@LFP, i.e., the positive electrode active material, was obtained. This positive electrode active material includes a positive electrode active material matrix and a coating layer on the surface of the positive electrode active material matrix. The coating layer includes Janus material, which consists of TiO2 and Ti3C2. The molar ratio of Ti3C2 to TiO2 is 1:1. The thickness of the coating layer is 88 nm. The Dv50 of the positive electrode active material is 1.2 μm. The mass percentage of Janus material in the positive electrode active material matrix is ​​1.2%.

[0092] Example 2

[0093] The preparation method of the positive electrode active material in Example 2 is basically the same as that in Example 1, except that titanium carbide is replaced with cobalt carbide. Janus material includes CoO and Co2C, which can be represented as CoO / Co2C.

[0094] Example 3

[0095] The preparation method of the positive electrode active material in Example 3 is basically the same as that in Example 1, except that titanium carbide is replaced with niobium carbide. Janus material includes NbO and Nb2C, which can be represented as NbO / Nb2C.

[0096] Example 4

[0097] The preparation method of the positive electrode active material in Example 4 is basically the same as that in Example 1, except that titanium carbide is replaced with iron carbide. The Janus material includes FeO and Fe3C, which can be represented as FeO / Fe3C.

[0098] Example 5

[0099] The preparation method of the positive electrode active material in Example 5 is basically the same as that in Example 1, except that titanium carbide is replaced with nickel carbide. Janus material includes NiO and Ni2C, which can be represented as NiO / Ni2C.

[0100] Example 6

[0101] The preparation method of the positive electrode active material in Example 6 is basically the same as that in Example 1, except that titanium carbide is replaced with molybdenum carbide. Janus material includes MoO and MoC, which can be represented as MoO / MoC.

[0102] Example 7

[0103] The preparation method of the positive electrode active material in Example 7 is basically the same as that in Example 1, except that the hydrothermal treatment temperature is 145°C and the time is 13h.

[0104] Example 8

[0105] The preparation method of the positive electrode active material in Example 8 is basically the same as that in Example 1, except that the hydrothermal treatment temperature is 160°C and the time is 14h.

[0106] Example 9

[0107] The preparation method of the positive electrode active material in Example 9 is basically the same as that in Example 1, except that the hydrothermal treatment temperature is 140°C and the time is 12h.

[0108] Example 10

[0109] The preparation method of the positive electrode active material in Example 10 is basically the same as that in Example 1, except that the hydrothermal treatment temperature is 180°C and the time is 16h.

[0110] Example 11

[0111] The preparation method of the positive electrode active material in Example 11 is basically the same as that in Example 1, except that the heat treatment temperature is 115℃.

[0112] Example 12

[0113] The preparation method of the positive electrode active material in Example 12 is basically the same as that in Example 1, except that the heat treatment temperature is 100℃.

[0114] Example 13

[0115] The preparation method of the positive electrode active material in Example 13 is basically the same as that in Example 1, except that the heat treatment temperature is 150°C.

[0116] Example 14

[0117] The preparation method of the positive electrode active material in Example 14 is basically the same as that in Example 1, except that the mass ratio of the positive electrode active material matrix to TiO2 / Ti3C2 powder is 1:0.026.

[0118] Example 15

[0119] The preparation method of the positive electrode active material in Example 15 is basically the same as that in Example 1, except that the mass ratio of the positive electrode active material matrix to TiO2 / Ti3C2 powder is 1:0.01.

[0120] Example 16

[0121] The preparation method of the positive electrode active material in Example 16 is basically the same as that in Example 1, except that the mass ratio of the positive electrode active material matrix to TiO2 / Ti3C2 powder is 1:0.05.

[0122] Example 17

[0123] The preparation method of the positive electrode active material in Example 17 is basically the same as that in Example 1, except that the hydrothermal treatment temperature is 120°C and the time is 10h.

[0124] Example 18

[0125] The preparation method of the positive electrode active material in Example 18 is basically the same as that in Example 1, except that the hydrothermal treatment temperature is 200℃ and the time is 20h.

[0126] Example 19

[0127] The preparation method of the positive electrode active material in Example 19 is basically the same as that in Example 1, except that the matrix of the positive electrode active material is lithium manganese iron phosphate.

[0128] Example 20

[0129] The preparation method of the positive electrode active material in Example 20 is basically the same as that in Example 1, except that the positive electrode active material matrix is ​​the ternary material NCM811.

[0130] Comparative Example 1

[0131] The positive electrode active material of Comparative Example 1 is lithium iron phosphate material, excluding the coating layer.

[0132] Comparative Example 2

[0133] The preparation method of the positive electrode active material in Comparative Example 2 is basically the same as that in Example 1, except that the coating layer only includes TiO2.

[0134] Comparative Example 3

[0135] The preparation method of the positive electrode active material of Comparative Example 3 is basically the same as that of Example 1, except that the coating layer only includes Ti3C2.

[0136] Comparative Example 4

[0137] The preparation method of the positive electrode active material of Comparative Example 4 is basically the same as that of Example 1, except that the coating layer includes a mixture of TiO2 and Ti3C2.

[0138] Experimental example:

[0139] 1. Coating thickness: The positive electrode active material of the examples and comparative examples was coated on aluminum foil, and a cross-section was obtained by shearing machine. The cross-section was photographed using a scanning electron microscope, and the thickness of more than 10 uniformly coated positions was measured using a ruler. The average value was taken to obtain the coating thickness.

[0140] 2. Positive electrode active material Dv50: The positive electrode active materials of the examples and comparative examples were dispersed in anhydrous ethanol, sonicated for 5 minutes, and then tested using a laser particle size analyzer.

[0141] 3. Electronic conductivity test: The electronic conductivity was measured using the AC impedance method on an Autolab electrochemical workstation at a frequency of 10 Hz. -2 Hz-10 6 Hz, the test conditions were room temperature (25℃).

[0142] 4. Charging Capacity Test: At 25℃ and normal pressure (0.1MPa), the positive electrode active material, binder PVDF, and conductive carbon black of each embodiment and comparative example were thoroughly mixed in N-methylpyrrolidone solvent at a mass percentage ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet containing a positive electrode active layer with a thickness of 100μm and an areal density of 10mg / cm³. 2 Then, the positive electrode sheet was punched into small round pieces with a diameter of 12mm using a film-making tool. After drying and weighing, it was assembled into a 1.6g / Ah coin cell in a glove box under an Ar protective atmosphere using a 2025 coin cell case, commercial graphite as the negative electrode, and the positive and negative electrodes were configured with an N / P ratio of 1.1:1. The coin cell was assembled together with conventional high-voltage lithium cobalt oxide electrolyte.

[0143] The test was conducted on a LAND workstation, where the battery was charged to 4.3V at 0.07C rate at 25°C to determine its charging capacity.

[0144] 5. Cyclic Performance Test: At 25℃ and atmospheric pressure (0.1MPa), the positive electrode active material, binder PVDF, and conductive carbon black of each embodiment and comparative example were mixed in a mass ratio of 8:1:1. N-methylpyrrolidone solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet was obtained. The negative electrode used graphite, and together with the separator polypropylene and the electrolyte (composed of 1mol / L LiPF6, solvent EC / DMC / DEC = v / v / v:1 / 1 / 1), a full cell was formed.

[0145] The battery was first cycled at 0.01C and within the range of 2.2V-4.3V to ensure thorough electrolyte wetting. After 5 cycles, it was subjected to 300 cycles at 25°C with a current of 0.5C, an upper limit voltage of 4.3V, and a lower limit voltage of 3V. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 300th cycle were measured. 300 The capacity retention rate after 300 cycles is Q = Q 300 / Q1×100%.

[0146] Figure 1 is a schematic diagram of the structure of the positive electrode active material of Embodiment 1 of this application.

[0147] As shown in Figure 1, the coating layer of the positive electrode active material in Example 1 includes metal carbides and metal oxides, i.e., Janus materials. They can exhibit both conductor and semiconductor properties in the same particle, and can form a directional electric field within the particle itself, which is an ordered state.

[0148] Figure 2 is a schematic diagram of the structure of the positive electrode active material of Comparative Example 4 of this application.

[0149] As shown in Figure 2, the coating layer of the positive electrode active material in Comparative Example 4 is a mixture of conductor and semiconductor, which is in a disordered state and electrons cannot move in a directional manner.

[0150] Table 1

[0151] As shown in Table 1, compared with the comparative example, the positive electrode active material provided in this application, by coating the surface of the positive electrode active material matrix with Janus material, which includes metal carbides and metal oxides, can form a Schottky junction on the surface of the positive electrode active material particles, thereby forming an electric field for unidirectional electron movement, accelerating the electron movement rate, thereby improving the electronic conductivity of the positive electrode active material, and enhancing the charging capacity and cycle performance of the battery.

[0152] A comparison of Examples 1-6 shows that the metal element Ti in Example 1 significantly improves the battery's charging capacity and cycle performance, resulting in a charging capacity of 163.63 mAh / g and a capacity retention rate of 90.12%. The metal element Ni in Example 5 also significantly improves the battery's charging capacity and cycle performance, resulting in a charging capacity of 163.06 mAh / g and a capacity retention rate of 89.39%.

[0153] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

A positive electrode active material, characterized in that, Includes a positive electrode active material matrix and a coating layer present on the surface of the positive electrode active material matrix; The coating layer comprises a janus material; the janus material comprises metal carbides and metal oxides. The positive electrode active material according to claim 1 is characterized in that, The janus material is obtained by partially oxidizing the metal carbide. The positive electrode active material according to claim 1 or 2 is characterized in that, The molar ratio of the metal carbide to the metal oxide is 1:(0.8-1.2). The positive electrode active material according to any one of claims 1-3 is characterized in that, The metal element in the metal carbide and / or the metal oxide includes at least one of Ti, Co, Nb, Fe, Ni and Mo. The positive electrode active material according to any one of claims 1-4 is characterized in that, The thickness of the coating layer is 50nm-200nm. The positive electrode active material according to any one of claims 1-5 is characterized in that, The Dv50 of the positive electrode active material is 1μm-1.5μm. The positive electrode active material according to any one of claims 1-6 is characterized in that, The Janus material accounts for 1%-5% of the mass percentage of the positive electrode active material matrix, preferably 1.2%-2.6%. The positive electrode active material according to any one of claims 1-7 is characterized in that, The positive electrode active material matrix includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, and ternary materials. A method for preparing a positive electrode active material according to any one of claims 1-8, characterized in that, Includes the following steps: 1) The metal carbide is subjected to hydrothermal treatment to obtain Janus material; 2) The raw material system including the Janus material and the positive electrode active material matrix is ​​subjected to heat treatment to obtain the positive electrode active material. The preparation method according to claim 9 is characterized in that, The temperature of the hydrothermal treatment is 140℃-180℃, preferably 145℃-160℃; And / or, the hydrothermal treatment time is 12h-16h, preferably 13h-14h. The preparation method according to claim 9 or 10 is characterized in that, The heat treatment temperature is 100℃-150℃, preferably 115℃-120℃. A positive electrode plate, characterized in that, It includes a positive electrode active layer, wherein the positive electrode active layer comprises the positive electrode active material according to any one of claims 1-8 or the positive electrode active material prepared by the preparation method according to any one of claims 9-11. A battery characterized in that, Includes the positive electrode sheet as described in claim 12. A battery pack, characterized in that, Includes the battery as described in claim 13. An electrical appliance, characterized in that, Includes the battery of claim 13 or the battery pack of claim 14.

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