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 an MXene material and a lithium-containing phosphoric acid salt material, the lithium-containing phosphoric acid salt material is located on the surface of the MXene material; and at least part of the lithium-containing phosphoric acid salt material is connected with the MXene material through a metal-oxygen chemical bond. The composite positive pole active material in the application has relatively high conductivity on the basis of not losing the basic performance of the lithium-containing phosphoric acid salt material and is suitable for a battery with relatively 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 the advantages of low cost and high safety, but their poor conductivity affects 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 described in this application 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 MXene material and lithium phosphate material, wherein the lithium phosphate material is located on the surface of the MXene material;

[0008] At least a portion of the lithium phosphate material is connected to the MXene material via metal-oxidation bonds.

[0009] MXene materials are a novel type of two-dimensional material composed of transition metal carbides, carbonitrides, or nitrides. They possess large and tunable interlayer spaces, excellent hydrophilicity and conductivity, and rich surface chemical properties. In the technical solution of this application, a lithium phosphate material is loaded onto the MXene material, and at least a portion of the lithium phosphate material is linked to the MXene material via metal-oxidation chemical bonds. Compared to simple mixing, the lithium phosphate material is more easily and uniformly distributed onto the MXene material, which is beneficial for improving the conductivity of the MXene material and helps improve the cycle performance of the battery cell. Simultaneously, compared to simple mixing, the method of... Chemical bonding accelerates the diffusion rate of active ions in lithium phosphate materials and helps improve the rate performance of individual battery cells. Furthermore, the chemical bonding strengthens the interaction between materials, resulting in higher structural stability of the lithium phosphate material. During electrode processing or actual battery use, MXene provides strong protection for the lithium phosphate material, preventing direct contact between the lithium phosphate material and the electrolyte and reducing side reactions. Therefore, the composite positive electrode active material described in this application exhibits high conductivity and structural stability without significantly compromising the basic performance of the lithium phosphate material, making it suitable for batteries with high requirements for cycle performance and rate performance.

[0010] In some embodiments, the mass content of the MXene material is 0.1%-2% based on the mass of the composite positive electrode active material.

[0011] In the technical solution of this application, the mass content of the MXene material is controlled within the above-mentioned range. While improving the conductivity of the lithium phosphate material, the proportion of the lithium phosphate material has a small impact, reducing the adverse effects of lithium phosphate material content loss on the performance of the battery cell. Moreover, with the mass content of the MXene material within the above-mentioned reasonable range, the adverse effects of the oxidation of the MXene material itself on the performance of the battery cell, especially the rate performance, can be reduced during the charging and discharging process.

[0012] In some embodiments, the Dv50 particle size of the lithium phosphate material is less than or equal to 1 μm.

[0013] 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 two-dimensional MXene material, 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.

[0014] 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 materials, can solve this problem. However, nanoparticles have a large specific surface area and are in direct contact with the electrolyte, leading to more side reactions. By linking at least part of the lithium phosphate material with MXene material through metal-oxidation bonds, the nano-sized lithium phosphate material is less prone to agglomeration, reducing the possibility of decreased conductivity and improving the overall performance of the battery cell. At the same time, the lithium phosphate material can also be fixedly loaded onto the MXene material, which provides protection and reduces the occurrence of side reactions.

[0015] In some embodiments, the composite positive electrode active material further includes a conductive agent.

[0016] In the technical solution of this application, MXene material is prone to oxidation during electrode processing or actual battery use, which affects its conductivity. Therefore, adding an additional conductive agent to the composite cathode material can compensate for the decrease in conductivity caused by the oxidation of MXene material, so that the composite cathode active material can still maintain good conductivity during use. In addition, it can reduce the amount of conductive agent used in the preparation of cathode sheet.

[0017] In some embodiments, at least a portion of the conductive agent is distributed between the MXene materials and is connected to the MXene materials via metal-oxide bonds.

[0018] In the technical solution of this application, MXene materials are prone to agglomeration during electrode processing or actual battery use, affecting their conductivity. Therefore, at least a portion of the conductive agent is distributed between the MXene materials and connected to the MXene materials through metal-oxidation bonds, forming a mutual binding effect, which reduces the occurrence of agglomeration of the conductive agent or MXene materials, especially reducing the adverse effects of MXene material agglomeration on the conductivity and other properties of the composite positive electrode active material. In addition, the binding effect of the conductive agent on the MXene materials is similar to the role of a binder in the system. Therefore, in the preparation of the positive electrode, the amount of binder can be reduced, which is beneficial to increasing the loading of the composite positive electrode active material in the positive electrode.

[0019] In some embodiments, based on the mass of the composite positive electrode active material, the mass content of the conductive agent is 0.1%-3%, optionally 0.1%-1%.

[0020] In the technical solution of this application, the mass content of the conductive agent is within the above-mentioned range. First, it can compensate for the decrease in conductivity of MXene material caused by oxidation or agglomeration during electrode processing or actual battery use. Second, it can form a good binding effect on MXene material, thereby improving the overall conductivity of the composite positive electrode active material. Finally, the content of the conductive agent within a suitable range has little impact on the proportion of lithium phosphate material, reducing the problem of reduced energy density caused by low lithium phosphate material content.

[0021] 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.

[0022] In the technical solution of this application, the surface of a one-dimensional conductive agent, a two-dimensional conductive agent, or a three-dimensional conductive agent can more easily connect at least two MXene materials. The conductive agent and the MXene material have strong mutual binding, which helps to reduce the agglomeration of the conductive agent and the MXene material and improve the conductivity of the positive electrode active material.

[0023] In some embodiments, the one-dimensional conductive agent includes carbon nanotubes.

[0024] In the technical solution of this application, carbon nanotubes have strong conductivity and a large specific surface area. Various defects on their surface can be chemically connected with MXene materials and bound together, thereby improving the structural stability and conductivity of the composite positive electrode active material.

[0025] In some embodiments, the two-dimensional conductive agent includes graphene.

[0026] In the technical solution of this application, graphene has strong conductivity and a large specific surface area. Both graphene and MXene are two-dimensional materials, which can be well entangled and bound together, thereby improving the structural stability and conductivity of the composite positive electrode active material.

[0027] In some embodiments, the three-dimensional conductive agent comprises porous carbon.

[0028] In the technical solution of this application, porous carbon has strong conductivity, large specific surface area, and more three-dimensional material connection sites, which can be well entangled and bound with MXene material, thereby improving the structural stability and conductivity of the composite positive electrode active material.

[0029] In some embodiments, the chemical formula of the lithium phosphate material is Li m Fe 1-x-y Mn x M yPO4, 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.

[0030] In the technical solution of this application, the above-mentioned lithium phosphate material has the advantages of low cost and high safety, and the composite positive electrode active material formed by the interaction with MXene material has excellent comprehensive performance.

[0031] Secondly, this application provides a method for preparing a single battery cell, the method comprising the following steps:

[0032] A composite positive electrode active material is obtained by mixing and reacting a phosphorus source, a lithium-containing metal source, and an MXene material with anionic groups on its surface.

[0033] 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;

[0034] The positive electrode is assembled to obtain a single battery cell.

[0035] In the technical solution of this application, the raw material phosphorus source and lithium metal source of lithium phosphate material are mixed and reacted with MXene material containing anionic groups on the surface. The metal cations of lithium metal source react with the anions in MXene material containing anionic groups on the surface, so that lithium phosphate material and MXene material are chemically connected to form metal-oxidation chemical bonds, thus obtaining composite positive electrode active material.

[0036] In some embodiments, the mixed raw materials also include conductive agents and / or surfactants.

[0037] In the technical solution of this application, a surfactant is added as needed during preparation, which can form a good dispersion effect on the other components of the system, such as MXene materials or conductive agents.

[0038] In some embodiments, the reaction temperature is 50-200°C; and / or;

[0039] The reaction time is 6-24 hours.

[0040] Thirdly, this application provides a battery device comprising a plurality of battery cells according to the first aspect.

[0041] 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.

[0042] 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

[0043] 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:

[0044] Figure 1 These are scanning electron microscope (SEM) images of composite positive electrode active materials from some embodiments of this application;

[0045] Among them, 1-Mxene material; 2-lithium iron phosphate; 3-carbon nanotubes. Detailed Implementation

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] Lithium phosphate materials have the advantages of low cost and high safety, but their conductivity is poor.

[0053] This application improves the conductivity of lithium phosphate materials by forming a composite positive electrode active material by linking MXene material and at least a portion of lithium phosphate material through metal-oxidation bonds. This application also provides a battery cell, a battery device, and an electrical device.

[0054] [Battery cell]

[0055] 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.

[0056] The battery cell can be a lithium-ion battery, a sodium lithium-ion battery, a lithium metal battery, a lithium sulfur battery, etc., and the embodiments of this application are not limited to this.

[0057] [Electrode Assembly]

[0058] 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 positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium 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.

[0059] [Positive electrode plate]

[0060] In some embodiments, the positive electrode can be a positive electrode sheet. This application provides a battery cell that includes a positive electrode sheet.

[0061] The positive electrode includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector;

[0062] The positive electrode film layer includes a composite positive electrode active material;

[0063] The composite positive electrode active material includes MXene material and lithium phosphate material, wherein the lithium phosphate material is located on the surface of the MXene material;

[0064] At least a portion of the lithium phosphate material is connected to the MXene material via metal-oxidation bonds.

[0065] In some embodiments, at least a portion of the lithium phosphate material is connected to the MXene material via iron-oxidation bonds and / or manganese-oxidation bonds; wherein the iron in the iron-oxidation bonds is trivalent and the manganese in the manganese-oxidation bonds is divalent.

[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, which 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, such as MXene and lithium phosphate 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, and then observe and take pictures to observe the morphology of the composite positive electrode active material. Specifically, observe at the composite position of lithium phosphate material and MXene material. Since there is no grain boundary mixing region in ordinary physical mixing, if an obvious grain boundary fusion region can be observed at the bonding position, it can be preliminarily judged that the lithium phosphate material and MXene material are connected by metal-oxidation chemical bonds.

[0070] (4) Analysis of the connection between lithium phosphate material and MXene material: Composite positive electrode active material, MXene 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 the infrared spectra of different samples. When the metal element in lithium phosphate material is bonded to oxygen-containing groups such as hydroxyl and carboxyl groups, the peak position will shift. By comparing the infrared spectra of MXene material, lithium phosphate material and composite positive electrode active material, the chemical bond between lithium phosphate material and MXene material was analyzed to determine the connection mode between the two.

[0071] MXene materials are a novel class of two-dimensional materials composed of transition metal carbides, carbonitrides, or nitrides. They possess large and tunable interlayer spaces, excellent hydrophilicity and conductivity, and rich surface chemical properties. As an example, in MXene materials, M represents a transition metal, such as chromium, molybdenum, manganese, iron, cobalt, copper, aluminum, silver, nickel, palladium, platinum, ruthenium, and titanium; X represents carbon or nitrogen.

[0072] In the technical solution of this application embodiment, a lithium phosphate material is loaded onto an MXene material, and at least a portion of the lithium phosphate material is connected to the MXene material by a metal-oxidation chemical bond. Compared to simple mixing, the lithium phosphate material is more easily and uniformly distributed on the MXene material, which helps improve the conductivity of the MXene material and improves the cycle performance of the battery cell. At the same time, compared to simple mixing, the chemical bond connection accelerates the diffusion rate of active ions in the lithium phosphate material and also helps improve the rate performance of the battery cell. Moreover, the chemical bond connection results in stronger interaction between materials, and the resulting lithium phosphate material has higher structural stability. During electrode processing or actual battery use, the MXene material provides stronger protection for the lithium phosphate material, making it less likely for the lithium phosphate material to directly contact the electrolyte and reducing the occurrence of side reactions. Therefore, the composite positive electrode active material described in this application has high conductivity and structural stability without significantly compromising the basic performance of the lithium phosphate material, making it suitable for batteries with high requirements for cycle performance and rate performance.

[0073] In some embodiments, based on the mass of the composite positive electrode active material, the mass content of the MXene material is 0.1%-2%, for example 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, etc.

[0074] In this application, the mass content of MXene material 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 a plasma excitation light source is used to evaporate and vaporize the sample, dissociating or decomposing it into an atomic state. The atoms may be further ionized into an ionic state, 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, and then photoelectric devices are used to detect the spectrum. The sample is qualitatively analyzed based on the measured spectral wavelengths, and the quantitative content is determined based on the intensity of the emitted light.

[0075] In the technical solution of this application embodiment, the mass content of the MXene material is controlled within the above-mentioned range. While improving the conductivity of the lithium phosphate material, the impact on the proportion of the lithium phosphate material is small, reducing the adverse effects of the loss of lithium phosphate material content on the performance of the battery cell. Moreover, with the mass content of the MXene material within the above-mentioned reasonable range, the adverse effects of the oxidation of the MXene material itself on the performance of the battery cell, especially the rate performance, can be reduced during the charging and discharging process.

[0076] In some embodiments, the Dv50 particle size of the lithium phosphate material is less than or equal to 1 μm, such as 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, 50 nm, etc., and optionally less than or equal to 100 nm.

[0077] 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.

[0078] 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 two-dimensional MXene material, mitigating the impact of the small-particle-size lithium phosphate material's own agglomeration on conductivity. Furthermore, the protective effect of the two-dimensional MXene on the small-particle-size material reduces the possibility of side reactions between the small-particle-size lithium phosphate material and the electrolyte, improving both the material's conductivity and cycle stability, thus balancing the kinetic and cycle performance of the battery cell.

[0079] In some embodiments, the composite positive electrode active material further includes a conductive agent.

[0080] In the technical solution of this application embodiment, MXene material is prone to oxidation during electrode processing or actual battery use, which affects its conductivity. Therefore, adding an additional conductive agent to the composite cathode material can compensate for the decrease in conductivity caused by the oxidation of MXene material, so that the composite cathode active material can still maintain good conductivity during use. In addition, it can reduce the amount of conductive agent used in the preparation of cathode sheet.

[0081] In some embodiments, at least a portion of the conductive agent is distributed between MXene materials and is connected to the MXene materials via metal-oxide bonds.

[0082] In this application, the composite positive electrode active material is ultrasonically mixed with ethanol and then dropped onto a microgrid. After the ethanol evaporates, the sample is prepared. Then, it is observed using a transmission electron microscope (such as the Hitachi HT7800 series, JEM2010EX, or Libra 200FE). If the conductive agent and MXene material are a whole, the preliminary analysis shows that the conductive agent and MXene material are chemically bonded. The composite positive electrode active material is then prepared into sheet-like samples of 0.1-1.0 mm by pressing. The infrared spectrum of the sample is obtained by Fourier transform infrared spectroscopy (such as TENSOR-27) to analyze the chemical bond between the conductive agent and MXene material.

[0083] In this application, the metal-oxidation bond between the conductive agent and the MXene material is formed by defects on the surface of the conductive agent, such as carboxyl or hydroxyl groups, and the metal elements of the MXene material.

[0084] In the technical solution of this application embodiment, MXene materials are prone to agglomeration during electrode processing or actual battery use, affecting their conductivity. Therefore, at least a portion of the conductive agent is distributed between the MXene materials and connected to the MXene materials through metal-oxide bonds, forming a mutual binding effect, reducing the occurrence of agglomeration of the conductive agent or MXene materials, and especially reducing the adverse effects of MXene material agglomeration on the conductivity and other properties of the composite positive electrode active material. In addition, the binding effect of the conductive agent on the MXene materials is similar to the role of a binder in the system. Therefore, in the preparation of the positive electrode, the amount of binder can be reduced, which is beneficial to increasing the loading of the composite positive electrode active material in the positive electrode.

[0085] In some embodiments, based on the mass of the composite positive electrode active material, the mass content of the conductive agent is 0.1%-3%, optionally 0.1%-1%; for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, etc.

[0086] In the technical solution of this application embodiment, the mass content of the conductive agent is within the above-mentioned range. First, it can compensate for the decrease in conductivity of MXene material caused by oxidation or agglomeration during electrode processing or actual battery use. Second, it can form a good binding effect on MXene material, thereby improving the overall conductivity of the composite positive electrode active material. Finally, the content of the conductive agent within a suitable range has little impact on the proportion of lithium phosphate material, reducing the problem of reduced energy density caused by low lithium phosphate material content.

[0087] In this application, for cost-saving purposes, the mass content of the conductive agent can be adjusted as needed within the range of 0.1%-1%.

[0088] 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.

[0089] In the technical solution of this application embodiment, the surface of a one-dimensional conductive agent, a two-dimensional conductive agent, or a three-dimensional conductive agent can more easily connect at least two pieces of MXene material. The conductive agent and the MXene material have strong mutual binding, which helps to reduce the agglomeration of the conductive agent and the MXene material and improve the conductivity of the lithium phosphate material.

[0090] In some embodiments, the one-dimensional conductive agent comprises carbon nanotubes.

[0091] In the technical solution of this application embodiment, carbon nanotubes have strong conductivity and large specific surface area. Various defects on the surface can be chemically connected with MXene materials and bound to each other, thereby further improving the structural stability and conductivity of the composite positive electrode active material.

[0092] In some embodiments, the two-dimensional conductive agent includes graphene.

[0093] In the technical solution of this application embodiment, graphene has strong conductivity and a large specific surface area. Both graphene and MXene are two-dimensional materials, which can be well entangled and bound together, thereby improving the structural stability and conductivity of the composite positive electrode active material.

[0094] In some embodiments, the three-dimensional conductive agent comprises porous carbon.

[0095] In the technical solution of this application embodiment, porous carbon has strong conductivity, large specific surface area, and more three-dimensional material connection sites, which can be well entangled and bound with MXene material, thereby improving the structural stability and conductivity of composite positive electrode active material.

[0096] In some embodiments, the chemical formula of the lithium phosphate material is Li m Fe 1-x-y Mn x M yPO4, 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.

[0097] Element M can exist in lithium phosphate materials as a dopant element, or as a coating element in the coating layer of lithium phosphate materials.

[0098] In the technical solution of this application embodiment, the above-mentioned lithium phosphate material has the advantages of low cost and high safety, and the composite positive electrode active material formed by the interaction with MXene material has excellent comprehensive performance.

[0099] In some embodiments, the positive electrode film layer further includes a binder and / or other conductive agents.

[0100] In some embodiments, the adhesive comprises 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.

[0101] In some embodiments, 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.

[0102] [Preparation of Composite Positive Electrode Active Materials]

[0103] This application provides a method for preparing a composite positive electrode active material, the method comprising the following steps:

[0104] The composite positive electrode active material is obtained by mixing and reacting a phosphorus source, a lithium-containing metal source, and an MXene material with anionic groups on its surface.

[0105] In the technical solution of this application embodiment, raw materials such as phosphorus source and lithium metal source containing lithium phosphate material are mixed and reacted with MXene material containing anionic groups on the surface. The metal cations of lithium metal source react with the anions in MXene material containing anionic groups on the surface, so that lithium phosphate material and MXene material are connected by metal-oxidation chemical bonds to obtain composite positive electrode active material.

[0106] In this application, the MXene material with anionic groups on its surface can be a commercially available product or it can be prepared in-house. For example, the MXene material with anionic groups on its surface is obtained by the following preparation method:

[0107] The MXene material was dispersed in acid, etched and stripped, the precipitate was collected and freeze-dried to obtain the MXene material with anionic groups on its surface.

[0108] As an example, the anionic functional groups in MXene materials with anionic groups on their surface can be hydroxyl (-OH), carboxyl (-COOH), etc.

[0109] As an example, the acid includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, hydrofluoric acid, or nitric acid.

[0110] As an example, the concentration of the acid is 0.5-3 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, etc.

[0111] As an example, the etching and stripping temperature is 10-80°C, such as 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, etc.

[0112] In some embodiments, the phosphorus source includes any one or a combination of at least two of (NH4)3PO4, (NH4)2HPO4, or (NH4)H2PO4.

[0113] In some embodiments, the lithium-containing metal source includes a lithium source.

[0114] In some embodiments, the lithium-containing metal source includes a lithium source and an iron source. Based on this, the metal-oxygen bond between the lithium phosphate material and the MXene material in this application is primarily an iron-oxygen bond.

[0115] In some embodiments, the lithium-containing metal source includes a lithium source, an iron source, and a manganese source. Based on this, the metal-oxygen bonds between the lithium phosphate material and the MXene material in this application are mainly iron-oxygen bonds and manganese-oxygen bonds.

[0116] In some embodiments, the lithium-containing metal source includes a lithium source and a manganese source. Based on this, the metal-oxygen bond between the lithium phosphate material and the MXene material in this application is primarily a manganese-oxygen bond.

[0117] In some embodiments, the lithium-containing metal source includes a lithium source, an iron source, and an M source, where M is selected from any one or a combination of at least two of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn, and Pb. Based on this, the metal-oxygen bond between the lithium phosphate material and the MXene material in this application is primarily an iron-oxygen bond.

[0118] In some embodiments, the lithium-containing metal source includes a lithium source, an iron source, a manganese source, and an M source, where M is selected from any one or a combination of at least two of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn, and Pb. Based on this, the metal-oxygen bonds between the lithium phosphate material and the MXene material in this application are mainly iron-oxygen bonds and manganese-oxygen bonds.

[0119] As an example, the lithium source includes any one or a combination of at least two of LiCl, Li2SO4, and LiNO3.

[0120] The iron source includes any one or a combination of at least two of FeCl3, Fe(NO3)3, and Fe2(SO4)3.

[0121] The manganese source includes any one or a combination of at least two of MnCl2, Mn(NO3)2, and MnSO4.

[0122] As an example, the molar ratio of phosphorus source to lithium-containing metal source is 1:1, and the element types are designed according to the type of positive electrode active material.

[0123] In some embodiments, the mixed raw materials further include conductive agents and / or surfactants.

[0124] In this application, during preparation, the conductive agent is selected that has surface defects, such as carboxyl or hydroxyl groups on its surface. This allows the carboxyl or hydroxyl groups of the conductive agent to form metal-oxygen bonds with the metal elements of the MXene material during preparation, achieving chemical bonding. Based on this, the metal-oxygen bond between the conductive agent and the MXene material in this application is mainly an M-oxygen bond. The choice of M depends on the type of MXene material, and M represents a transition metal, such as chromium, molybdenum, manganese, iron, cobalt, copper, aluminum, silver, nickel, palladium, platinum, ruthenium, titanium, etc.

[0125] In the technical solution of this application embodiment, a surfactant is added as needed during preparation, which can form a good dispersion effect on the other components of the system, such as MXene materials or conductive agents.

[0126] In this application, the cationic surfactant, which is not easily decomposed under high temperature and electrochemical action and can be adsorbed on the active material, is more conducive to the preparation of the composite positive electrode active material. The reason is that when preparing the composite positive electrode active material, the surface of the MXene material has more anions, and the cationic surfactant is more easily adsorbed on the surface of the MXene material, thereby improving the dispersibility of the MXene material.

[0127] As an example, the surfactant includes cationic surfactants, including but not limited to any one or a combination of at least two of dodecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, or betaine.

[0128] As an example, the mixing is carried out in a solvent such as water.

[0129] As an example, the mixing is carried out under stirring, wherein the stirring time can be 0.5-5h, such as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, etc.

[0130] In some embodiments, the reaction temperature is 50-200°C, for example 100°C, 150°C, etc.; and / or;

[0131] The reaction time is 6-24 hours, for example, 8 hours, 10 hours, 15 hours, 20 hours, etc.

[0132] In some embodiments, the composite positive electrode active material is obtained by the following preparation method:

[0133] A phosphorus source, a lithium-containing metal source, and an MXene material with anionic groups on its surface are dispersed in a solvent such as water. Optionally, a conductive agent with surface defects and / or a cationic surfactant are also included. The mixture is stirred and mixed for 0.5-5 hours, and then reacted at 50-200°C for 6-24 hours. The resulting precipitate is the composite positive electrode active material.

[0134] In the technical solution of this application embodiment, the raw materials are mixed in water and heated to react, which belongs to the hydrothermal coprecipitation method. This method prepares nano-sized lithium phosphate materials while forming metal-oxidation bonds between the metal elements such as iron and manganese in the lithium phosphate materials and the anionic groups such as carboxyl or hydroxyl groups on the surface of the MXene materials, thus achieving chemical connection. It can also distribute conductive agents between the MXene materials and form metal-oxidation bonds between the carboxyl or hydroxyl groups on the surface of the conductive agents and the metal elements in the MXene materials, thus achieving chemical connection. This application can prepare composite positive electrode active materials with excellent comprehensive performance through a simple method.

[0135] [Preparation of the positive electrode sheet]

[0136] 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 (such as amino acid surfactants) 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 drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0137] In this application, MXene material may cause the composite positive electrode active material to agglomerate, affecting its performance. Therefore, surfactants, such as amino acid surfactants, can be added as needed.

[0138] [Negative electrode plate]

[0139] 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.

[0140] 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.).

[0141] In some embodiments, the negative electrode film layer comprises a negative electrode active material.

[0142] 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.

[0143] 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.

[0144] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0145] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0146] [Preparation of the negative electrode sheet]

[0147] 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.

[0148] [Isolation Component]

[0149] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] [Electrolytes]

[0154] 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.

[0155] Liquid electrolytes include electrolyte salts and solvents.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0160] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0161] 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.

[0162] 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.

[0163] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0164] [Structure of the electrode assembly]

[0165] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0166] In some embodiments, the electrode assembly is a wound structure. The positive electrode and the negative electrode are wound into a wound structure.

[0167] In some implementations, the electrode assembly is a stacked structure.

[0168] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0169] 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.

[0170] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0171] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0172] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0173] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0174] 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.

[0175] [shell]

[0176] 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.

[0177] 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.

[0178] 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.

[0179] [Electrode terminals]

[0180] 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.

[0181] [Pressure relief mechanism]

[0182] 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.

[0183] 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.

[0184] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0185] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0186] 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.

[0187] 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.

[0188] 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.

[0189] [Battery Device]

[0190] 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.

[0191] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] [ Electrical appliances ]

[0200] 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.

[0201] [Example]

[0202] Example 1

[0203] Positive electrode sheet:

[0204] (1) Preparation of MXene material with anions on the surface: Purchased MX material (purchased from Aladdin, brand name 12363-89-2, M is Ti, X is C) was dispersed in acid (HF) with a concentration of 1 mol / L and etched and peeled at 50℃ to form MXene material with anions (-OH, -COOH) on the surface.

[0205] (2) Preparation of composite positive electrode active material: The MXene material, conductive agent (carbon nanotubes CNT with carboxyl and hydroxyl groups on the surface), Fe source (Fe2(SO4)3), Li source (Li2CO3), P source ((NH4)3PO4), and surfactant (glycine) from step (1) were dispersed in a solvent (water) and stirred for 1 h. Then, the mixture was heated at 120 °C for 12 h in a reaction vessel. The molar ratio of Fe source, Li source, and P source was 1:1:1. A precipitate was obtained, which is the composite positive electrode material (LFP / MXene material / CNT composite material). The mass percentage of MXene material was 0.5%, the mass percentage of conductive agent was 0.5%, and the mass percentage of surfactant was 0.2%. Its scanning electron microscope image is shown below. Figure 1As shown, lithium iron phosphate 2 is distributed on MXene material 1, and different MXene materials are connected to both sides of the wall of carbon nanotube 3, proving that the composite positive electrode active material has been successfully prepared.

[0206] (3) Preparation of positive electrode sheet: The composite positive active material obtained in step (2) is mixed with conductive agent (carbon black) in the mass ratio of binder (polyvinylidene fluoride) and amino acid surfactant (glycine) = 8.5:0.2:0.3:0.5 and then added to solvent (N-methylpyrrolidone) to form positive electrode slurry; the positive electrode slurry is then coated on the positive current collector (aluminum foil) to form positive electrode film layer, and after drying, cold pressing and slitting, positive electrode sheet is obtained.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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 stacked battery, namely the battery cell, is formed.

[0211] Examples 2-7 and Comparative Examples 1-4

[0212] Except for the parameters in Table 1, the battery cells were obtained according to the method described in Example 1.

[0213] Table 1: Information on the components of the composite positive electrode active material

[0214]

[0215] In the table, the total mass of the composite positive electrode active material is 100%, and the total mass of MXene material, conductive agent and positive electrode active material is 100%; "—" indicates content not involved; LFP refers to lithium iron phosphate, LMP refers to lithium manganese phosphate, and LMFP refers to lithium manganese iron phosphate.

[0216] Comparative Example 3

[0217] This comparative example provides a composite positive electrode active material, which uses traditional carbon coating for LFP. The specific preparation method includes the following steps:

[0218] Iron oxalate (FeC2O4), LiH2PO4 and carbon were mixed in a solvent at a ratio of 1:1:0.2 and milled in a sand. Methanol was a suitable solvent. The milling time was 8 hours. Particles were prepared by spraying. Carbon-coated lithium iron phosphate was then obtained by high-temperature sintering at 700°C for 8 hours.

[0219] Comparative Example 4

[0220] The key difference between this comparative example and Example 1 is that the MXene material, lithium phosphate material, and conductive agent in the composite positive electrode active material do not form chemical bonds. Specifically, the composite positive electrode active material is obtained by the following preparation method:

[0221] The composite positive electrode active material was obtained by stirring lithium iron phosphate, unmodified MXene material and conductive agent for 1 hour and heating at 120°C for 12 hours.

[0222] [Performance Testing]

[0223] (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 0.5C to 0% SOC. The discharge capacity C1 was recorded. Following this method, the discharge capacity C2 at 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.

[0224] The test results are summarized in Table 2.

[0225] Table 2

[0226]

[0227] Analysis of Comparative Examples 1-2 and Examples 1-2 shows that the capacity retention rate of Comparative Examples 1-2 at a 4C discharge rate is not as good as that of Examples 1-2, proving that the composite positive electrode active material, including MXene material and lithium phosphate material, is more conducive to improving the rate performance of battery cells and improving the dynamic performance of the battery.

[0228] Analysis of Comparative Example 3 and Example 2 shows that the capacity retention rate of Comparative Example 3 at a 4C discharge rate is not as good as that of Example 1, proving that the composite positive electrode active material of this application is more conducive to improving the rate performance of battery cells than traditional carbon-coated lithium phosphate materials.

[0229] Analysis of Comparative Example 4 and Example 1 shows that the capacity retention rate of Comparative Example 4 at a 4C discharge rate is not as good as that of Example 1. This proves that at least part of the lithium phosphate material and the MXene material are connected by metal-oxidation bonds to form a composite positive electrode active material, which is more conducive to improving the rate performance of the battery cell.

[0230] Analysis of Example 2 and Example 1 shows that the capacity retention rate of Example 2 at a 4C discharge rate is not as good as that of Example 1, 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.

[0231] Analysis of Examples 3-4 and Example 1 shows that the capacity retention rate of Examples 3-4 at a 4C discharge rate is not as good as that of Example 1, proving that the mass content of MXene material in the composite positive electrode active material is 0.1%-2%, which is more conducive to improving the rate performance of the battery cell.

[0232] Analysis of Example 5 and Example 1 shows that the capacity retention rate of Example 5 at a 4C discharge rate is not as good as that of Example 1, proving that the mass content of the conductive agent in the composite positive electrode active material is 0.1%-3%, which is more conducive to improving the rate performance of the battery cell.

[0233] (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%.

[0234] The test results are summarized in Table 3.

[0235] Table 3

[0236]

[0237]

[0238] Analysis of Comparative Examples 1-2 and Example 1 shows that the capacity retention rate of Comparative Examples 1-2 after 50 cycles is not as good as that of Example 1-2, proving that the composite positive electrode active materials, including MXene materials and lithium phosphate materials, have better conductivity and are more conducive to improving the cycle performance of battery cells.

[0239] Analysis of Comparative Example 3 and Example 2 shows that the capacity retention rate of Comparative Example 3 after 50 cycles is not as good as that of Example 2, which proves that the composite positive electrode active material of this application has better conductivity than the traditional carbon-coated lithium phosphate material and is more conducive to improving the cycle performance of the battery cell.

[0240] Analysis of Comparative Example 4 and Example 1 shows that the capacity retention rate of Comparative Example 4 after 50 cycles is not as good as that of Example 1, which proves that the composite positive electrode active material formed by at least part of the lithium phosphate material and the MXene material being connected by metal-oxidation bonds has better conductivity and is more conducive to improving the cycle performance of the battery cell.

[0241] Analysis of Example 2 and Example 1 shows that the capacity retention rate of Example 2 after 50 cycles is not as good as that of Example 1, proving that the composite positive electrode active material contains a conductive agent, which is more conducive to improving the cycle performance of the battery cell.

[0242] Analysis of Examples 3-4 and Example 1 shows that the capacity retention rate of Examples 3-4 after 50 cycles is not as good as that of Example 1, proving that the mass content of MXene material in the composite positive electrode active material is 0.1%-2%, which is more conducive to improving the cycle performance of the battery cell.

[0243] Analysis of Examples 5 and 1 shows that the capacity retention rate of Example 5 after 50 cycles is not as good as that of Example 1, proving that the mass content of the conductive agent in the composite positive electrode active material of 0.1%-3% is more conducive to improving the cycle performance of the battery cell.

[0244] 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 MXene material and lithium phosphate material, wherein the lithium phosphate material is located on the surface of the MXene material; At least a portion of the lithium phosphate material is connected to the MXene material via metal-oxygen bonds.

2. The battery cell according to claim 1, characterized in that, Based on the mass of the composite positive electrode active material, the mass content of the MXene material is 0.1%-2%.

3. The battery cell according to claim 1 or 2, characterized in that, The Dv50 particle size of the lithium phosphate material is less than or equal to 1 μm.

4. The battery cell according to any one of claims 1-3, characterized in that, The composite positive electrode active material also includes a conductive agent.

5. The battery cell according to claim 4, characterized in that, At least a portion of the conductive agent is distributed between the MXene materials and is connected to the MXene materials via metal-oxide bonds.

6. The battery cell according to claim 4 or 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%-3%, optionally 0.1%-1%.

7. The battery cell according to any one of claims 4-6, 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.

8. The battery cell according to claim 7, characterized in that, The one-dimensional conductive agent includes carbon nanotubes.

9. The battery cell according to claim 7 or 8, characterized in that, The two-dimensional conductive agent includes graphene.

10. The battery cell according to any one of claims 7-9, characterized in that, The three-dimensional conductive agent comprises porous carbon.

11. The battery cell according to any one of claims 1-10, 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.

12. A method for preparing a single battery cell, characterized in that, The preparation method includes the following steps: A composite positive electrode active material is obtained by mixing and reacting a phosphorus source, a lithium-containing metal source, and an MXene material with anionic groups on its surface. 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.

13. The preparation method according to claim 12, characterized in that, The mixed raw materials also include conductive agents and / or surfactants.

14. The preparation method according to claim 12 or 13, characterized in that, The reaction temperature is 50-200℃; and / or; The reaction time is 6-24 hours.

15. A battery device, characterized in that, The battery device includes a plurality of battery cells according to any one of claims 1-11.

16. An electrical appliance, characterized in that, The electrical device includes a battery cell according to any one of claims 1-11, or a battery cell obtained by the preparation method according to any one of claims 12-14, or a battery device according to claim 15.

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