Battery cell, battery device, and electric device

Abstract

The application relates to the technical field of batteries, in particular to a battery monomer, a battery device and a power utilization device. The battery monomer comprises a positive pole sheet; the positive pole sheet comprises a positive pole current collector and a positive pole film layer arranged on at least one surface of the positive pole current collector; the positive pole film layer comprises a composite positive pole active material; the composite positive pole active material comprises a conductive agent and a lithium-containing phosphate material, the lithium-containing phosphate material is located on the surface of the conductive agent, at least part of the lithium-containing phosphate material is connected with the conductive agent through a metal-oxygen chemical bond; and the lithium-containing phosphate material comprises lithium-containing phosphate particles and a coating layer at least partially coated on the lithium-containing phosphate particles, and the coating layer contains carbon elements. The composite positive pole active material disclosed by the application has higher conductivity on the basis of not losing the basic performance of the lithium-containing phosphate material, and is suitable for batteries with high requirements on cycle performance and rate performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Lithium phosphate materials have unique advantages in battery cell applications due to their high safety and low cost, but their poor conductivity can affect the performance of battery cells in practical applications. Summary of the Invention

[0003] In view of the above problems, this application provides a battery cell, a battery device, and an electrical device. The composite positive electrode active material has high conductivity without losing the basic performance of lithium phosphate materials, and is suitable for batteries with high requirements for cycle performance and rate performance.

[0004] In a first aspect, this application provides a battery cell, the battery cell including a positive electrode sheet;

[0005] The positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector;

[0006] The positive electrode film layer includes a composite positive electrode active material;

[0007] The composite positive electrode active material includes a conductive agent and a lithium phosphate material, wherein the lithium phosphate material is located on the surface of the conductive agent, and at least a portion of the lithium phosphate material is connected to the conductive agent through a metal-oxidation bond.

[0008] The lithium-containing phosphate material includes lithium-containing phosphate particles and a coating layer that at least partially coats the lithium-containing phosphate particles, the coating layer containing carbon.

[0009] In the technical solution of this application, at least a portion of the lithium phosphate material and the conductive agent are linked by metal-oxidation chemical bonds. That is, at least a portion of the lithium phosphate material is chemically loaded onto the conductive agent. Compared with simple mixing, the lithium phosphate material and the conductive agent are more easily and uniformly dispersed. Compared with physical mixing, chemical bonding makes the combination of the two more compact and stable, which is beneficial for the transport of lithium ions and electrons by the conductive agent, improves the conductivity and ion conduction of the active material, and helps to improve the cycle performance and rate performance of the battery cell. At the same time, the direct connection between the lithium phosphate material and the conductive agent accelerates the lithium phosphate material… The increased diffusion rate of active ions helps improve the rate performance of individual battery cells; moreover, the use of chemical bonding strengthens the interaction forces between materials, which is beneficial to improving the structural stability of the composite cathode active material; in addition, the surface of the lithium phosphate material has a coating layer, which not only improves the structural stability of the composite cathode active material, but also reduces the contact between the lithium phosphate material and the electrolyte, thus reducing the occurrence of side reactions; therefore, the composite cathode active material described in this application has high conductivity and structural stability without losing the basic performance of the lithium phosphate material, and is suitable for batteries with high requirements for cycle performance and rate performance.

[0010] In some embodiments, the conductive agent includes any one or a combination of at least two of one-dimensional, two-dimensional, or three-dimensional conductive agents.

[0011] In the technical solutions of this application, the one-dimensional conductive agent, two-dimensional conductive agent, or three-dimensional conductive agent has a large specific surface area, and the surface can better load lithium phosphate materials, so as to achieve uniform dispersion of conductive agent and lithium phosphate materials, reduce their respective agglomeration effects, and facilitate the formation of stable battery cells.

[0012] In some embodiments, the one-dimensional conductive agent includes carbon nanotubes.

[0013] In the technical solution of this application, carbon nanotubes have strong conductivity and can be combined with lithium phosphate materials to form a three-dimensional conductive network, which is beneficial to improving the conductivity of lithium phosphate materials. Moreover, by utilizing the defects on the surface of the carbon nanotube wall, chemical bonding can be achieved with lithium phosphate materials to form a composite positive electrode active material with high structural stability and excellent rate performance. In addition, the use of additional conductive agents can be reduced when preparing the positive electrode slurry.

[0014] In some embodiments, the two-dimensional conductive agent includes graphene.

[0015] In the technical solution of this application, graphene has strong conductivity, which is beneficial to improve the conductivity of lithium phosphate materials; moreover, by utilizing the defects on its sheet surface, it can achieve chemical connection with lithium phosphate materials to form a composite positive electrode active material with high structural stability.

[0016] In some embodiments, the three-dimensional conductive agent comprises porous carbon.

[0017] In the technical solution of this application, porous carbon has strong conductivity, and its three-dimensional structure can better support lithium phosphate materials and achieve chemical connection with them to form a composite positive electrode active material with excellent conductivity and high structural stability.

[0018] In some embodiments, the mass content of the conductive agent is 0.1%-5% based on the mass of the composite positive electrode active material.

[0019] In the technical solution of this application, the mass content of the conductive agent in the composite positive electrode active material is within the above-mentioned range. While improving the conductivity of the lithium phosphate-containing material, the impact on its mass ratio is minimal, reducing the adverse effects of lithium phosphate-containing material content loss on the performance of the battery cell.

[0020] In some embodiments, the coating layer is derived from MOF materials.

[0021] MOFs are materials with specific structures formed by the electrostatic adsorption of metal ions and negatively charged organic ligands. MOFs have advantages such as large specific surface area, abundant porosity and tunable structure.

[0022] In the technical solution of this application, a coating layer derived from MOFs material is used. The coating layer is obtained by sintering and carbonizing organic ligands. While improving the structural stability of the composite positive electrode active material, the metal ions in the MOFs material can be used to form nano-sized lithium phosphate materials, thereby improving the conductivity of the lithium phosphate materials and the dynamic performance of the battery cells. At the same time, the metal ions in the MOFs material form metal-oxidation bonds with the conductive agent, further improving the conductivity of the lithium phosphate materials.

[0023] In some embodiments, the mass content of the coating layer is 0.1%-0.5% based on the mass of the lithium phosphate material.

[0024] In the technical solution of this application, based on the mass of the lithium phosphate material, the mass content of the coating layer is within the above-mentioned range. On the one hand, this facilitates uniform distribution on the surface of the lithium phosphate material, making it easier to form a composite positive electrode active material with high structural stability; on the other hand, within this mass content range, in actual use, the coating layer has little impact on the diffusion rate of active ions in the lithium phosphate material, reducing the possibility of performance degradation of the battery cell.

[0025] In some embodiments, the Dv50 particle size of the lithium phosphate material is less than or equal to 1 μm.

[0026] In the technical solution of this application, controlling the Dv50 particle size of the lithium phosphate material within a small range can further improve the conductivity of the lithium phosphate material and improve the kinetic performance of the battery cell. Simultaneously, this application loads the small-particle-size lithium phosphate material onto a conductive agent, reducing the possibility of side reactions between the small-particle-size lithium phosphate material and the electrolyte, thereby improving both the kinetic performance of the battery and the cycle performance of the battery cell.

[0027] Some lithium phosphate materials, such as lithium iron phosphate, have low active ion diffusion coefficients due to their one-dimensional ion transport channel characteristics. Controlling the Dv50 particle size of lithium phosphate materials within the aforementioned range, i.e., nano-sized, can solve this problem and improve their conductivity. However, nanoparticles have a large specific surface area and come into direct contact with the electrolyte, leading to more side reactions. By chemically linking at least part of the lithium phosphate material with a conductive agent, the nano-sized lithium phosphate material is less prone to agglomeration and can be fixedly loaded onto the conductive agent. The conductive agent then provides protection, reducing the possibility of side reactions.

[0028] In some embodiments, the chemical formula of the lithium phosphate material is Li m Fe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y≤1, 0.8≤m≤1.15, M is selected from any one or at least two combinations of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb.

[0029] In the technical solution of this application, the above-mentioned lithium phosphate material has the advantages of low cost and high safety, and interacts with the conductive agent to form a composite positive electrode active material with excellent comprehensive performance, thereby improving the performance of the battery cell.

[0030] In some implementations, x is selected from 0 or 1.

[0031] In the technical solution of this application, x is selected from 0 or 1, and the lithium phosphate material belongs to lithium iron phosphate material or lithium manganese phosphate material, which facilitates the preparation of nano-sized lithium phosphate materials of MOFs materials, as well as the preparation of composite positive electrode active materials with excellent conductivity and structural stability, thereby improving the performance of battery cells.

[0032] In some embodiments, at least a portion of the lithium phosphate material is connected to the conductive agent via an iron-oxidation bond or a manganese-oxidation bond.

[0033] In the technical solution of this application, at least a portion of the lithium phosphate material and the conductive agent are connected through iron-oxidation bonds or manganese-oxidation bonds, which facilitates the participation of MOFs materials in the preparation of lithium phosphate materials, forming a composite positive electrode active material with excellent conductivity and structural stability, so as to improve the cycle performance and rate performance of the battery cell.

[0034] Secondly, this application provides a method for preparing a single battery cell, the method comprising the following steps:

[0035] A coating layer is formed on the surface of lithium phosphate particles to form a lithium phosphate material, and the lithium phosphate material is connected to a conductive agent through a metal-oxidation bond to obtain a composite positive electrode active material.

[0036] The composite positive electrode active material is formulated into a positive electrode slurry, and then the positive electrode slurry is coated on at least one surface of the positive electrode current collector to form a positive electrode film layer, thereby obtaining a positive electrode sheet;

[0037] The positive electrode is assembled to obtain a single battery cell.

[0038] In some embodiments, the preparation method includes:

[0039] A precipitate is obtained by mixing a metal compound, an organic ligand, and a conductive agent with surface defects in a solvent and precipitating them.

[0040] The precipitate, lithium source, and phosphorus source are then mixed and sintered to obtain the composite positive electrode active material.

[0041] Thirdly, this application provides a battery device comprising a plurality of battery cells according to the first aspect.

[0042] Fourthly, this application provides an electrical device comprising the battery cell described in the first aspect, or the battery cell obtained by the preparation method described in the second aspect, or the battery device described in the third aspect.

[0043] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0044] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0045] Figure 1 Transmission electron microscope (TEM) images of composite positive electrode active materials from some embodiments of this application;

[0046] Among them, 1-lithium phosphate material; 2-carbon nanotubes. Detailed Implementation

[0047] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0048] 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 pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0049] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0050] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0051] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is also expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "2-10" indicates that all real numbers between "2-10" have been listed in this article; "2-10" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0053] Lithium phosphate materials have unique advantages in battery cell applications due to their high safety and low cost, but their conductivity is relatively poor.

[0054] This application improves the conductivity of lithium phosphate materials by linking at least a portion of the lithium phosphate material with a conductive agent via metal-oxidation bonds, thereby obtaining a high-performance battery. This application also provides a battery cell, a battery device, and an electrical device.

[0055] [Battery cell]

[0056] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0057] The battery cell can be a lithium-ion battery, a sodium-lithium-ion battery, a lithium metal battery, a lithium-sulfur battery, a magnesium-ion battery, etc., and the embodiments of this application are not limited to this.

[0058] [Electrode Assembly]

[0059] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the negative and positive electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions or sodium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0060] [Positive electrode plate]

[0061] In some embodiments, the positive electrode can be a positive electrode sheet. This application provides a battery cell that includes a positive electrode sheet.

[0062] The positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector;

[0063] The positive electrode film layer includes a composite positive electrode active material;

[0064] The composite positive electrode active material includes a conductive agent and a lithium phosphate material, wherein the lithium phosphate material is located on the surface of the conductive agent, and at least a portion of the lithium phosphate material is connected to the conductive agent through a metal-oxidation bond.

[0065] The lithium-containing phosphate material includes lithium-containing phosphate particles and a coating layer that at least partially coats the lithium-containing phosphate particles, the coating layer containing carbon.

[0066] In this application, the composite positive electrode active material in the positive electrode film layer is tested using the following method:

[0067] (1) Separation of composite positive electrode active material: Disassemble the battery cell to obtain the positive electrode sheet, and then peel the positive electrode film from the surface of the positive electrode current collector; then separate the composite positive electrode active material from the positive electrode film by solvent dissolution method, specifically by dissolving the positive electrode film in a solvent (such as N-methylpyrrolidone NMP), separating the composite positive electrode active material from the solvent by vacuum filtration, collecting the solid material on the filter paper, drying it, and obtaining the composite positive electrode active material.

[0068] (2) Composition analysis of composite positive electrode active materials: The composition of composite positive electrode active materials is mainly analyzed by X-ray diffraction. Specifically, the composite positive electrode active material is ground into a sample between 10-80 μm and fixed on the sample stage. The cathode in the X-ray tube is heated to generate an electron flow that bombards the anode target. The anode target slows down the electrons and emits X-rays of a specific wavelength. Through means such as slits or monochromatic crystals, the wavelength of the X-rays is controlled within a narrow range and has the same direction. The X-rays diffract with the crystal to be tested on the sample stage to produce a diffraction pattern. The position and intensity of the diffraction peaks are recorded using a detector to form a diffraction pattern, which is the XRD pattern. The collected pattern is matched with known phases in a standard database (such as JCPDS Powder Diffraction File or ICSD). Different materials have different diffraction peak positions (2θ angle). By comparing the position and relative intensity of the diffraction peaks, the phases present in the sample are identified.

[0069] (3) Morphological analysis of composite positive electrode active material: The composite positive electrode active material was sonicated in ethanol, and the sonicated mixture was dropped onto copper foil. After drying, it was tested using a transmission electron microscope (such as Hitachi HT7800 series transmission scanning electron microscope, or JEM2010EX, or Libra 200FE). Specifically, ensure that the vacuum system is running normally. First, use the focusing device of the transmission electron microscope system to adjust the focus of the sample. Then, select an appropriate electron beam energy and magnification (e.g., 100k) according to the properties of the sample. Then, observe and take pictures to observe the morphology of the composite positive electrode active material and the distribution of the conductive agent. Specifically, observe at the location where the lithium phosphate material and the conductive agent are combined. If a clear grain boundary fusion zone can be observed at the bonding location, since there is no grain boundary fusion zone in ordinary physical mixing, it is preliminarily judged that the lithium phosphate material and the conductive agent are connected by metal-oxidation chemical bonds. At the same time, observe at the location of the lithium phosphate material. It can be observed that the surface of the lithium phosphate particles contains a coating layer.

[0070] (4) Analysis of the connection mode between lithium phosphate material and conductive agent: Composite positive electrode active material and lithium phosphate material were prepared into sheet samples of 0.1-1.0 mm by pressing. Fourier transform infrared spectroscopy (such as TENSOR-27) was used to obtain infrared spectra of different samples. When metal elements in lithium phosphate material are bonded to oxygen-containing groups such as hydroxyl and carboxyl groups, the peak position will shift. By comparing the infrared spectra of lithium phosphate material and composite positive electrode active material, the chemical bond between lithium phosphate material and conductive agent was analyzed to determine the connection mode between the two.

[0071] In the technical solution of this application, at least a portion of the lithium phosphate material and the conductive agent are linked by metal-oxidation chemical bonds. That is, at least a portion of the lithium phosphate material is chemically loaded onto the conductive agent. Compared with simple mixing, the lithium phosphate material and the conductive agent are more easily and uniformly dispersed. Compared with physical mixing, chemical bonding makes the combination of the two more compact and stable, which is beneficial for the transport of lithium ions and electrons by the conductive agent, improves the conductivity and ion conduction of the active material, and helps to improve the cycle performance and rate performance of the battery cell. At the same time, the direct connection between the lithium phosphate material and the conductive agent accelerates the lithium phosphate material… The increased diffusion rate of active ions helps improve the rate performance of individual battery cells; moreover, the use of chemical bonding strengthens the interaction forces between materials, which is beneficial to improving the structural stability of the composite cathode active material; in addition, the surface of the lithium phosphate material has a coating layer, which not only improves the structural stability of the composite cathode active material, but also reduces the contact between the lithium phosphate material and the electrolyte, thus reducing the occurrence of side reactions; therefore, the composite cathode active material described in this application has high conductivity and structural stability without losing the basic performance of the lithium phosphate material, and is suitable for batteries with high requirements for cycle performance and rate performance.

[0072] In some embodiments, the conductive agent includes any one or a combination of at least two of one-dimensional conductive agents, two-dimensional conductive agents, or three-dimensional conductive agents.

[0073] In the technical solutions of the embodiments of this application, the one-dimensional conductive agent, two-dimensional conductive agent or three-dimensional conductive agent has a large specific surface area, and the surface can better load lithium phosphate material, realize the uniform dispersion of conductive agent and lithium phosphate material, reduce their respective agglomeration effect, and facilitate the formation of battery cells with stable performance.

[0074] In some embodiments, the one-dimensional conductive agent comprises carbon nanotubes.

[0075] In the technical solution of this application embodiment, carbon nanotubes have strong conductivity and can be combined with lithium phosphate materials to form a three-dimensional conductive network, which is beneficial to improving the conductivity of lithium phosphate materials. Moreover, by utilizing the defects on the surface of the carbon nanotube wall, chemical bonding can be achieved with lithium phosphate materials to form a composite positive electrode active material with high structural stability and excellent rate performance. In addition, the use of additional conductive agents can be reduced when preparing the positive electrode slurry.

[0076] In some embodiments, the two-dimensional conductive agent includes graphene.

[0077] In the technical solution of this application embodiment, graphene has strong conductivity, which is beneficial to improve the conductivity of lithium phosphate materials; moreover, by utilizing the defects on its sheet surface, it can achieve chemical connection with lithium phosphate materials to form a composite positive electrode active material with high structural stability.

[0078] In some embodiments, the three-dimensional conductive agent comprises porous carbon.

[0079] In the technical solution of this application embodiment, porous carbon has strong conductivity, and its three-dimensional structure can better support lithium phosphate materials and achieve chemical connection with them to form a composite positive electrode active material with excellent conductivity and high structural stability.

[0080] In some embodiments, based on the mass of the composite positive electrode active material, the mass content of the conductive agent is 0.1%-2%, for example 0.1%, 0.3%, 0.5%, 1%, 2%, etc.

[0081] In the technical solution of this application embodiment, the mass content of the conductive agent in the composite positive electrode active material is within the above-mentioned range. While improving the conductivity of the lithium phosphate-containing material, the impact on its mass ratio is minimal, reducing the adverse effects of lithium phosphate-containing material content loss on the performance of the battery cell.

[0082] In some embodiments, the coating layer is derived from MOF materials.

[0083] MOFs are materials with specific structures formed by the electrostatic adsorption of metal ions and negatively charged organic ligands. MOFs have advantages such as large specific surface area, abundant porosity and tunable structure.

[0084] In the technical solution of this application embodiment, a coating layer derived from MOFs material is used. The coating layer is obtained by sintering and carbonizing organic ligands. While improving the structural stability of the composite positive electrode active material, the metal ions in the MOFs material can be used to form nano-sized lithium phosphate materials, thereby improving the conductivity of the lithium phosphate materials and improving the dynamic performance of the battery cells. At the same time, the metal ions in the MOFs material form metal-oxidation bonds with the conductive agent, further improving the conductivity of the lithium phosphate materials.

[0085] In some embodiments, based on the mass of the lithium phosphate material, the mass content of the coating layer is 0.1%-0.5%, for example 0.2%, 0.3%, 0.4%, etc.

[0086] In this application, the mass content of the coating layer can be tested using methods known in the art. For example, inductively coupled plasma (ICP) technology can be used for testing; specifically, an inductively coupled plasma emission spectrometer is used, where the sample is vaporized and dissociated or decomposed into atomic states by using a plasma excitation light source. The atoms may be further ionized into ionic states, and the atoms and ions are excited to emit light in the light source. Then, a spectroscopic system is used to decompose the light emitted by the light source into a spectrum arranged by wavelength. After that, a photoelectric device is used to detect the spectrum, and the sample is qualitatively analyzed based on the measured spectral wavelengths, and the content is quantitatively determined based on the intensity of the emitted light.

[0087] In the technical solution of this application embodiment, based on the mass of the lithium phosphate material, the mass content of the coating layer is within the above-mentioned range. On the one hand, this facilitates uniform distribution on the surface of the lithium phosphate material, making it easier to form a composite positive electrode active material with high structural stability; on the other hand, within this mass content range, in actual use, the coating layer has little impact on the diffusion rate of active ions in the lithium phosphate material, reducing the possibility of performance degradation of the battery cell.

[0088] In some embodiments, the Dv50 particle size of the lithium phosphate material is less than or equal to 100 nm, such as 100 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 5 nm, etc., and optionally less than or equal to 10 nm.

[0089] In this application, the Dv50 particle size refers to the particle size corresponding to a cumulative volume distribution of 50% in the particle size distribution. This application obtains the Dv50 particle size using laser diffraction or electron microscopy; specifically, laser diffraction analyzes the particle size distribution by measuring the scattered light signal generated by the laser light emitted by the particles; electron microscopy observes the particle size in different fields of view using scanning electron microscopy or transmission electron microscopy and performs statistical analysis.

[0090] In the technical solution of this application embodiment, controlling the Dv50 particle size of the lithium phosphate material within a small range can further improve the conductivity of the lithium phosphate material and improve the kinetic performance of the battery cell. Simultaneously, this application loads the small-particle-size lithium phosphate material onto a conductive agent, reducing the possibility of side reactions between the small-particle-size lithium phosphate material and the electrolyte, thereby improving both the kinetic performance of the battery and the cycle performance of the battery cell.

[0091] Some lithium phosphate materials, such as lithium iron phosphate, have low active ion diffusion coefficients due to their one-dimensional ion transport channel characteristics. Controlling the Dv50 particle size of lithium phosphate materials within the aforementioned range, i.e., nano-sized, can solve this problem and improve their conductivity. However, nanoparticles have a large specific surface area and come into direct contact with the electrolyte, leading to more side reactions. By chemically linking at least part of the lithium phosphate material with a conductive agent, the nano-sized lithium phosphate material is less prone to agglomeration and can be fixedly loaded onto the conductive agent. The conductive agent then provides protection, reducing the possibility of side reactions.

[0092] In some embodiments, the chemical formula of the lithium phosphate material is Li m Fe 1-x-y Mn x M y PO4, 0.8≤m≤1.15 (e.g. 0.9, 1, 1.0, 1.1, etc.), 0≤x≤1 (e.g. 0.2, 0.4, 0.6, 0.8, etc.), 0≤y≤1 (e.g. 0.2, 0.4, 0.6, 0.8, etc.), M is selected from any one or at least two combinations of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn, and Pb.

[0093] In the technical solution of this application embodiment, the above-mentioned lithium phosphate material has the advantages of low cost and high safety, and interacts with the conductive agent to form a composite positive electrode active material with excellent comprehensive performance, thereby improving the performance of the battery cell.

[0094] In some embodiments, x is selected from 0 or 1.

[0095] In the technical solutions of this application embodiment, x is selected from 0 or 1, and the lithium phosphate material belongs to lithium iron phosphate material or lithium manganese phosphate material, which facilitates the preparation of nano-sized lithium phosphate materials of MOFs materials, as well as the preparation of composite positive electrode active materials with excellent conductivity and structural stability, thereby improving the performance of battery cells.

[0096] In some embodiments, at least a portion of the lithium phosphate material is connected to the conductive agent via an iron-oxidation bond or a manganese-oxidation bond.

[0097] In the technical solution of this application embodiment, at least a portion of the lithium phosphate material and the conductive agent are connected through iron-oxidation chemical bonds or manganese-oxidation chemical bonds, which facilitates the participation of MOF materials in the preparation of lithium phosphate materials, forming a composite positive electrode active material with excellent conductivity and structural stability, so as to improve the cycle performance and rate performance of the battery cell.

[0098] In some embodiments, the positive electrode film layer further includes other conductive agents. As an example, the other conductive agents include any one or a combination of at least two of carbon black (such as acetylene black, Ketjen black, etc.), carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0099] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder includes any one or a combination of at least two of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0100] [Preparation of Composite Positive Electrode Active Materials]

[0101] In some embodiments, this application provides a method for preparing a composite positive electrode active material, the method comprising the following steps:

[0102] A coating layer is formed on the surface of lithium phosphate particles to form a lithium phosphate material, and the lithium phosphate material is connected to a conductive agent through a metal-oxidation bond to obtain a composite positive electrode active material.

[0103] In some embodiments, the preparation method includes:

[0104] A precipitate is obtained by mixing a metal compound, an organic ligand, and a conductive agent with surface defects in a solvent and precipitating them.

[0105] The precipitate, lithium source, and phosphorus source are then mixed and sintered to obtain the composite positive electrode active material.

[0106] In the technical solution of this application embodiment, during the process of forming a precipitate from a metal compound, an organic ligand, and a conductive agent with surface defects, the metal ions in the metal compound simultaneously connect with the organic ligand and the conductive agent with surface defects, mix and precipitate, and the resulting precipitate is a conductive agent connected with MOFs material.

[0107] Furthermore, the precipitate, lithium source, and phosphorus source are mixed and sintered. The metal ions in the MOF material react with the lithium and phosphorus sources to form a lithium phosphate material, which combines with defects on the surface of the conductive agent to form metal-oxidation chemical bonds, achieving chemical connection. That is, the lithium phosphate material is loaded on the surface of the conductive agent. At the same time, the sintering process can also remove excess defects on the surface of the conductive agent, further improving the conductivity of the lithium phosphate material. Moreover, the unsaturated bonds in the organic ligands will decompose and carbonize, forming a coating layer on the surface of the lithium phosphate material.

[0108] Through the above process, the composite positive electrode active material of this application is obtained.

[0109] As an example, the conductive agent used in this application in the mixed precipitation has defects on its surface, such as containing oxygen-containing functional groups such as carboxyl or hydroxyl groups.

[0110] In some embodiments, in the Raman spectrum of a conductive agent with surface defects, I d / I g It ranges from 0.9 to 1.2, for example, 1.0, 1.1, etc.

[0111] In this application, the Raman spectrum of the conductive agent with surface defects was obtained using a laser Raman spectrometer, model BWS435-532SY. Specifically, the intensity of the D peak and G peak of the sample was compared, where the D peak (approximately 1350 cm⁻¹) was the most significant. -1 The peak (G) represents a defect in the carbon atom lattice, while the peak (G peak, approximately 1580 cm⁻¹) represents a defect in the carbon atom lattice. -1 ) represents the in-plane stretching vibration of sp2 hybridized carbon atoms; I d / I g The larger the ratio, the more defects there are in the carbon atom crystal.

[0112] As an example, carbon nanotubes are chosen as conductive agents because they have a large aspect ratio and high flexibility, making them prone to entanglement and aggregation. However, using MOF (Metal-Oxide-Factory) materials to derive the coating layer, such as growing MOF materials on the walls of carbon nanotubes, increases the stiffness of the carbon nanotubes. Furthermore, during the formation of MOF materials, the carbon nanotubes are fixed together at specific sites under the influence of organic ligands and metal ions, reducing entanglement and aggregation. Therefore, when preparing the cathode slurry, the use of additional conductive agents and other additives such as dispersants can be reduced.

[0113] As an example, the metal ions in the metal compounds used in this application have a valence state of at least +2, such as Fe. 3+ and Mn 2+ wait.

[0114] In some embodiments, the metal compound includes iron-based compounds. Based on this, the lithium phosphate material and the conductive agent in this application are linked via iron-oxide chemical bonds.

[0115] In some embodiments, the metal compound includes manganese compounds. Based on this, the lithium phosphate material and the conductive agent in this application are linked via manganese-oxidation chemical bonds.

[0116] In some embodiments, the metal compound includes iron compounds and manganese compounds. Based on this, the lithium phosphate material of this application is linked to the conductive agent via iron-oxygen and manganese-oxygen chemical bonds.

[0117] As an example, iron compounds include any one or a combination of at least two of FeCl3, Fe(NO3)3, Fe2(SO4)3, and Fe2O3.

[0118] As an example, manganese compounds include any one or a combination of at least two of MnCl2, Mn(NO3)2, and MnSO4.

[0119] As an example, the organic ligands used in this application have two or more functional groups, where the functional groups refer to anionic groups such as carboxyl groups and amino groups; for example, the organic ligands include aromatic hydrocarbon organic compounds containing functional groups such as nitrogen, oxygen, and fluorine, such as any one or a combination of at least two of terephthalic acid, trimesic acid, or diaminoterephthalic acid.

[0120] As an example, the molar ratio of the metal compound to the organic ligand is 1:(3-8), where 3-8 can be 4, 5, 6, 7, etc.

[0121] As an example, the mixed precipitation is carried out in a solvent, wherein the solvent includes one or more of methanol, ethanol, and ethylene glycol; the mixed precipitation time is 1-40 h, for example 5 h, 10 h, 20 h, 30 h, etc.

[0122] As an example, the mass ratio of solvent to metal compound is (3-8):1, where 3-8 can be 4, 5, 6, 7, etc.

[0123] In this application, during the electrostatic adsorption process, high-valence metal ions and multiple organic ligands are interconnected on a three-dimensional topological plane to form a specific structure. In order to reduce the surface energy during the bonding process between the metal ions and the organic ligands, the organic ligands and metal ions have a fixed bonding angle, thus forming a regular and fixed pore structure. In the above-mentioned mode of action, when the metal ions form metal-oxidation bonds with the conductive agent with surface defects, the conductive agent is more likely to form a three-dimensional network structure, reducing the aggregation of the conductive agent and improving the conductivity of the lithium phosphate material.

[0124] In some embodiments, the sintering temperature is 400-800°C, for example 500°C, 600°C, 700°C, etc.; and / or;

[0125] The sintering time is 1-10 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, etc.

[0126] As an example, the phosphorus source includes any one or a combination of at least two of (NH4)3PO4, (NH4)2HPO4, or (NH4)H2PO4.

[0127] As an example, the lithium source includes any one or a combination of at least two of Li3PO4, Li2CO3, LiCl, Li2SO4, and LiNO3.

[0128] In this application, the molar ratio of phosphorus source to lithium source or metal compound is designed according to the type of lithium phosphate material.

[0129] In some embodiments, the preparation method of the composite positive electrode active material includes the following steps:

[0130] (1) Mix the metal compound, organic ligand and conductive agent with surface defects in a solvent and precipitate for 1-40 h to obtain a precipitate;

[0131] In this study, the molar ratio of the metal compound to the organic ligand is 1:(3-8); the mass ratio of the solvent to the metal compound is (3-8):1. In the Raman spectrum of the conductive agent with surface defects (e.g., carboxyl groups or hydroxyl groups), I... d / I g The value is 0.9-1.2;

[0132] (2) The precipitate, lithium source and phosphorus source are mixed and sintered at 400-800℃ for 1-10h to obtain the composite positive electrode active material.

[0133] [Preparation of the positive electrode sheet]

[0134] In some embodiments, the method for preparing the positive electrode sheet includes: dissolving a positive electrode material, such as a composite positive electrode active material, other conductive agents (such as carbon black), a binder (such as polyvinylidene fluoride), and other arbitrary components in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector (such as aluminum foil); and then drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0135] [Negative electrode plate]

[0136] In some embodiments, the negative electrode may be a negative electrode sheet, which includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface (e.g., one or two) of the negative electrode current collector.

[0137] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0138] In some embodiments, the negative electrode film layer comprises a negative electrode active material.

[0139] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0140] In some embodiments, the negative electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not have a negative electrode active material.

[0141] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0142] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0143] [Preparation of the negative electrode sheet]

[0144] In some embodiments, a negative electrode material, such as a negative electrode active material (e.g., graphite), a conductive agent (e.g., carbon black), a binder (e.g., styrene-butadiene rubber), and other arbitrary components (e.g., dispersants) are dissolved in a solvent (e.g., water) to form a negative electrode slurry; the negative electrode slurry is coated onto the surface of a negative electrode composite current collector (e.g., copper foil) to form a negative electrode film layer, and then dried, cold-pressed, and slit to obtain a negative electrode sheet.

[0145] [Isolation Component]

[0146] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0147] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0148] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0149] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0150] [Electrolytes]

[0151] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0152] Liquid electrolytes include electrolyte salts and solvents.

[0153] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0154] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0155] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0156] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0157] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0158] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0159] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium germanium phosphorus sulfide, silver sulfide germanium ore), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0160] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0161] [Structure of the electrode assembly]

[0162] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0163] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0164] In some implementations, the electrode assembly is a stacked structure.

[0165] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0166] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0167] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0168] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0169] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0170] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0171] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0172] [shell]

[0173] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0174] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0175] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0176] [Electrode terminals]

[0177] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0178] [Pressure relief mechanism]

[0179] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0180] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby creating an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0181] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0182] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0183] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0184] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0185] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0186] [Preparation of battery cells]

[0187] In some embodiments, the preparation of the battery cell includes the following steps:

[0188] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain a battery cell; the battery cell is placed in an outer packaging, electrolyte is added, and after vacuum sealing, standing, formation, shaping, capacity measurement and other processes, the battery cell is obtained.

[0189] As an example, a battery cell may include one or more positive electrode plates, separators, or negative electrode plates.

[0190] In some embodiments, a positive electrode, a separator, a negative electrode, a separator, and a positive electrode are stacked and wound in sequence to obtain a battery cell; the battery cell is placed in an outer packaging, an electrolyte is added, and after vacuum sealing, standing, formation, shaping, capacity measurement, and other processes, the battery cell is obtained.

[0191] [Battery Device]

[0192] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0193] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0194] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0195] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0196] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0197] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0198] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0199] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0200] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0201] [ Electrical appliances ]

[0202] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0203] [Example]

[0204] Example 1

[0205] Positive electrode sheet:

[0206] (1) Preparation of composite positive electrode active materials:

[0207] A metal compound (FeCl3), an organic ligand (trimethylbenzene acid), and a conductive agent with surface defects (carboxyl and hydroxyl groups) (carbon nanotubes CNTs, Raman spectroscopy I) are used. d / I g The solution was stirred in a solvent (methanol) for 24 hours to mix and precipitate, then filtered and dried to obtain the precipitate.

[0208] The molar ratio of the metal compound to the organic ligand is 1:3; the mass ratio of the solvent to the metal compound is 30:1.

[0209] A precipitate, lithium source (Li₂CO₃), and phosphorus source ((NH₄)₃PO₄) in a molar ratio of 1:1:1 were mixed and sintered at 600℃ for 8 hours to obtain a composite positive electrode active material. Its transmission electron microscopy (TEM) image is shown below. Figure 1 As shown, lithium phosphate material 1 (lithium iron phosphate with a coating layer on its surface) is loaded on the wall of carbon nanotube 2, proving that a composite positive electrode active material has been successfully prepared.

[0210] The molar amount is based on the metal elements in the precipitate, the lithium elements in the lithium source, and the phosphorus elements in the phosphorus source.

[0211] (2) Preparation of positive electrode sheet: The composite positive active material obtained in step (1): conductive agent (carbon black): binder (polyvinylidene fluoride) = 9:0.5:0.5 are mixed according to the mass ratio and added to the solvent (N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is then coated on the positive electrode current collector (aluminum foil) to form a positive electrode film layer. After drying, cold pressing and slitting, the positive electrode sheet is obtained.

[0212] Negative electrode sheet: Artificial graphite, conductive carbon black, carboxymethyl cellulose and solvent water are uniformly mixed in a weight ratio of 95:2:3:100 to form a negative electrode slurry, which is then coated on the negative electrode current collector copper foil to form a negative electrode film. After drying, cold pressing and slitting, the negative electrode sheet is obtained.

[0213] Electrolyte: Ethyl carbonate, diethyl carbonate, and dimethyl carbonate are mixed in a volume ratio of 1:1:1. Lithium hexafluorophosphate (LiPF6) is dissolved in the above solution to obtain the electrolyte. The concentration of LiPF6 in this electrolyte is 1 mol / L.

[0214] Separating membrane: A 13μm thick polyethylene membrane is used as the base membrane of the separating membrane, a 1μm ceramic layer is located on the surface of the base membrane, and a 2μm adhesive layer is located on the surface of the ceramic layer; specifically, ceramic particles and adhesive are sequentially sprayed onto the surface of the polyethylene membrane. The ceramic material is boehmite, accounting for 39wt% of the total mass of the separating membrane; the adhesive is polyacrylate, accounting for 5wt% of the total mass of the separating membrane, thus obtaining the separating membrane.

[0215] Assembly: The positive electrode, separator, negative electrode, separator and positive electrode are stacked and wound in sequence to obtain the battery cell; the battery cell is placed in the outer packaging, electrolyte is added, and after vacuum sealing, standing, formation, shaping and capacity testing, a battery cell is formed.

[0216] Examples 2-7 and Comparative Examples 1-2

[0217] Except for the parameters in Table 1, the battery cells were obtained according to the method described in Example 1.

[0218] Table 1: Raw Material and Composition Information of Composite Positive Electrode Active Materials

[0219]

[0220] In the table, "—" indicates data not involved; LFP refers to lithium iron phosphate, and LMP refers to lithium manganese phosphate; the mass content of the coating layer is based on the mass of the lithium phosphate material; the mass content of the conductive agent is based on the mass of the composite positive electrode active material; the connection method refers to the connection method between the lithium phosphate material and the conductive agent.

[0221] Comparative Example 2 involves first performing conventional carbon coating on LFP, followed by physical mixing with a conductive agent. The specific preparation method includes the following steps:

[0222] The metal compound (FeCl3) and organic ligand (tristyric acid) were stirred in a solvent (methanol) for 24 h to form a precipitate. The precipitate was then filtered and dried to obtain a precipitate. The precipitate, lithium source (Li2CO3), and phosphorus source ((NH4)3PO4) in a molar ratio of 1:1:1 were mixed and sintered at 600 °C for 8 h to obtain a positive electrode active material. The obtained positive electrode material was then mixed with CNTs in a mass ratio of 99.7:0.3.

[0223] [Performance Testing]

[0224] (1) Rate test: The battery cell was charged at 0.33C at 25℃ to 100% SOC. After charging, it was left to stand for 5 minutes, and then discharged at 0.33C to 0% SOC. The discharge capacity C1 was recorded. Following this method, the capacity C2 of 0.33C charging and 4C discharging was recorded. The capacity retention rate was C2 / C1×100%. The better the capacity retention rate of the battery cell at high charging rates, the better the rate performance of the battery cell.

[0225] The test results are summarized in Table 2.

[0226] Table 2

[0227]

[0228] Analysis of Comparative Example 1 and Example 1 shows that the capacity retention rate of Comparative Example 1 is lower than that of Example 1 at different rates, proving that the composite positive electrode active material contains a conductive agent, which is more conducive to improving the rate performance of the battery cell.

[0229] Analysis of Comparative Example 2 and Example 1 shows that the capacity retention rate of Comparative Example 2 is lower than that of Example 1 at different rates, proving that the composite positive electrode active material formed by the metal-oxidation bond connection of lithium phosphate material and conductive agent is more conducive to improving the rate performance of battery cells.

[0230] Analysis of Examples 2-3 and Example 1 shows that the capacity retention rate of Examples 2-3 is lower than that of Example 1 at different rates, proving that the mass content of the conductive agent in the composite positive electrode active material is more conducive to improving the rate performance of the battery cell when it is in the range of 0.1%-2%.

[0231] Analysis of Examples 4-5 and Example 1 shows that the capacity retention rate of Examples 4-5 is lower than that of Example 1 at different rates, proving that with the mass of lithium phosphate material as the benchmark, the composite positive electrode active material formed with the mass content of the coating layer in the range of 0.1%-0.5% is more conducive to improving the rate performance of the battery cell.

[0232] (2) Cyclic Test: The battery cell was charged at 0.33C at 25℃ to 100% SOC. After charging, it was left to rest for 5 minutes, and then discharged at 1C to 0% SOC. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery cell, and the discharge capacity C50 of the battery was recorded after the 50th cycle. The capacity retention rate of the battery cell after 50 cycles was P50 = C50 / C0 × 100%.

[0233] The test results are summarized in Table 3.

[0234] Table 3

[0235] Capacity retention rate after 50 cycles / % Example 1 85.9 Example 2 81.4 Example 3 83.2 Example 4 80.6 Example 5 79.8 Example 6 79.4 Example 7 73.2 Comparative Example 1 70.5 Comparative Example 2 71.5

[0236] Analysis of Comparative Example 1 and Example 1 shows that the capacity retention rate of Comparative Example 1 after 50 cycles is lower than that of Example 1, proving that the composite positive electrode active material containing a conductive agent has better conductivity and is more conducive to improving the cycle performance of the battery cell.

[0237] Analysis of Comparative Example 2 and Example 1 shows that the capacity retention rate of Comparative Example 2 after 50 cycles is lower than that of Example 1, proving that the composite positive electrode active material formed by the metal-oxidation bond connection of lithium phosphate material and conductive agent has better conductivity and is more conducive to improving the cycle performance of battery cells.

[0238] Analysis of Examples 2-3 and Example 1 shows that the capacity retention rate of Examples 2-3 after 50 cycles is lower than that of Example 1, proving that the conductivity of the conductive agent in the composite positive electrode active material is better when the mass content is in the range of 0.1%-2%, which is more conducive to improving the cycle performance of the battery cell.

[0239] Analysis of Examples 4-5 and Example 1 shows that the capacity retention rate of Examples 4-5 after 50 cycles is lower than that of Example 1. This proves that, based on the mass of lithium phosphate material, when the mass content of the coating layer is in the range of 0.1%-0.5%, the resulting composite positive electrode active material has better conductivity and is more conducive to improving the cycle performance of the battery cell.

[0240] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized in that, The battery cell includes a positive electrode sheet; The positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector; The positive electrode film layer includes a composite positive electrode active material; The composite positive electrode active material includes a conductive agent and a lithium phosphate material, wherein the lithium phosphate material is located on the surface of the conductive agent, and at least a portion of the lithium phosphate material is connected to the conductive agent through a metal-oxidation bond. The lithium-containing phosphate material includes lithium-containing phosphate particles and a coating layer that at least partially coats the lithium-containing phosphate particles, the coating layer containing carbon.

2. The battery cell according to claim 1, characterized in that, The conductive agent includes any one or a combination of at least two of one-dimensional, two-dimensional, or three-dimensional conductive agents.

3. The battery cell according to claim 2, characterized in that, The one-dimensional conductive agent includes carbon nanotubes.

4. The battery cell according to claim 2 or 3, characterized in that, The two-dimensional conductive agent includes graphene.

5. The battery cell according to any one of claims 2-4, characterized in that, The three-dimensional conductive agent comprises porous carbon.

6. The battery cell according to any one of claims 1-5, characterized in that, Based on the mass of the composite positive electrode active material, the mass content of the conductive agent is 0.1%-2%.

7. The battery cell according to any one of claims 1-6, characterized in that, The coating layer is derived from MOF materials.

8. The battery cell according to any one of claims 1-7, characterized in that, Based on the mass of the lithium phosphate material, the mass content of the coating layer is 0.1%-0.5%.

9. The battery cell according to any one of claims 1-8, characterized in that, The Dv50 particle size of the lithium phosphate material is less than or equal to 1 μm.

10. The battery cell according to any one of claims 1-9, characterized in that, The chemical formula of the lithium phosphate material is Li m Fe 1-x-y Mn x M y PO4, 0.8≤m≤1.15, 0≤x≤1, 0≤y≤1, M is selected from any one or at least two combinations of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb.

11. The battery cell according to claim 9, characterized in that, x equals 0 or 1.

12. The battery cell according to claim 10 or 11, characterized in that, At least a portion of the lithium phosphate material is connected to the conductive agent via iron-oxidation bonds or manganese-oxidation bonds.

13. A method for preparing a single battery cell, characterized in that, The preparation method includes the following steps: A coating layer is formed on the surface of lithium phosphate particles to form a lithium phosphate material, and the lithium phosphate material is connected to a conductive agent through metal-oxidation bonds; The composite positive electrode active material is formulated into a positive electrode slurry, and then the positive electrode slurry is coated on at least one surface of the positive electrode current collector to form a positive electrode film layer, thereby obtaining a positive electrode sheet; The positive electrode is assembled to obtain a single battery cell.

14. The preparation method according to claim 13, characterized in that, The preparation method includes: A precipitate is obtained by mixing a metal compound, an organic ligand, and a conductive agent with surface defects in a solvent and precipitating them. The precipitate, lithium source, and phosphorus source are then mixed and sintered to obtain the composite positive electrode active material.

15. A battery device, characterized in that, The battery device comprises a plurality of battery cells according to any one of claims 1-12.

16. An electrical appliance, characterized in that, The electrical device includes a battery cell according to any one of claims 1-12, or a battery cell obtained by the preparation method according to claim 13 or 14, or a battery device according to claim 15.

Images