Lithium ion secondary battery, preparation method and electric equipment

Abstract

The invention relates to the technical field of lithium ion secondary batteries, in particular to a lithium ion secondary battery, a preparation method and electric equipment. The lithium ion secondary battery comprises a positive pole piece, the positive pole piece comprises a positive active material layer, the positive active material layer comprises a lithium-containing transition metal phosphate composite material and spinel structure lithium manganate, and the lithium-containing transition metal phosphate composite material comprises lithium-containing transition metal phosphate and a coating layer, the coating layer is arranged on the surface of the lithium-containing transition metal phosphate, and the coating layer comprises a carbon-containing material. The contact angle between the lithium-containing transition metal phosphate composite material and water is A1, the contact angle between the spinel-structure lithium manganate and water is A2, and the ratio of A1 to A2 is 0.8-1.2. The ratio of the contact angle of the lithium-containing transition metal phosphate composite material to the contact angle of the spinel-structure lithium manganate is within the range, so that the machinability of the slurry prepared by mixing the two materials can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion secondary battery, a preparation method and an electric device. BACKGROUND

[0002] In recent years, lithium ion secondary batteries are widely used in wireless communication, transportation, aerospace and other aspects. During the charging and discharging process of the lithium ion secondary battery, the solid electrolyte interface film (SEI film) on the surface of the negative electrode is destroyed, thereby continuously consuming lithium ions in the lithium ion secondary battery, resulting in capacity attenuation. Therefore, the battery material is modified, and the process of the lithium ion secondary battery is difficult to manufacture. SUMMARY

[0003] Therefore, the technical problem to be solved by the present application is that the process of the lithium ion secondary battery is difficult to manufacture, and the present application provides a lithium ion secondary battery, a preparation method and an electric device, which can improve the manufacturing process of the lithium ion secondary battery.

[0004] To solve the above technical problems, the technical scheme of the first aspect adopted by the present application is to provide a lithium ion secondary battery including a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including a lithium-containing transition metal phosphate composite material and spinel structure lithium manganate, the lithium-containing transition metal phosphate composite material including a lithium-containing transition metal phosphate and a coating layer, the coating layer being disposed on the surface of the lithium-containing transition metal phosphate, the coating layer including a carbon-containing material, the contact angle of the lithium-containing transition metal phosphate composite material with water being A1, the contact angle of the spinel structure lithium manganate with water being A2, and the ratio of A1 to A2 being 0.8-1.2.

[0005] In the embodiments of the present application, the positive electrode sheet in the lithium ion secondary battery comprises a lithium-containing transition metal phosphate composite material and spinel-structured lithium manganate. The lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate have different surface energies due to different chemical bonds. The difference in surface energy of the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate can be reflected by the ratio of the contact angles of the two materials with the same solvent. The ratio of the contact angles of the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate with water is controlled to be between 0.8 and 1.2, so that the attractive force or repulsive force of the two materials to the same solvent or other substances is similar, and then when the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate are mixed together to prepare a slurry, the attractive force and repulsive force of the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate to the solvent, the conductive agent and other substances in the slurry are similar, so that the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate can be uniformly dispersed in the slurry. Reducing the phenomenon of particle agglomeration in the slurry when the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate are mixed together to prepare a slurry can solve the problem of uneven mixing of the lithium-containing transition metal phosphate composite material, the spinel-structured lithium manganate and the conductive agent, etc., which ultimately leads to problems such as unevenness of the prepared positive electrode sheet, poor film forming performance and poor conductivity, and thus the specific capacity and electrochemical performance such as the life of the lithium ion secondary battery can be improved. In the embodiments of the present application, the lithium ion secondary battery comprising the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate can improve the dispersibility of the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate when preparing a slurry, and thus improve the processability of the slurry prepared by mixing the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate together. In the embodiments of the present application, the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganate are mixed to prepare an active material layer, so that the carbon-containing material coating layer on the surface of the lithium-containing transition metal phosphate can adsorb the manganese ions dissolved from the spinel-structured lithium manganate, reduce the damage of the manganese ions to the solid electrolyte interface film (SEI film) on the surface of the negative electrode sheet, and improve the cycle stability of the lithium ion secondary battery. In the embodiments of the present application, the carbon-containing material is coated on the surface of the lithium-containing transition metal phosphate, so that the specific surface area of the carbon-containing material is large and the performance of adsorbing the manganese ions dissolved from the spinel-structured lithium manganate is good.

[0006] In any embodiment, the lithium-containing transition metal phosphate composite material comprises secondary particles, the secondary particles comprise primary microparticles, the volume average particle size DV50 of the secondary particles is 4-10 μm, and the average particle size of the primary microparticles is 100-2000 nm. In the embodiment, the average particle size of the primary microparticles is small, i.e., 100-2000 nm. Therefore, the secondary particles formed by agglomeration of the primary microparticles have a large specific surface area, which is beneficial to improve the transmission rate of lithium ions, thereby improving the electrochemical performance of the lithium ion secondary battery. The volume average particle size DV50 of the secondary particles of the lithium-containing transition metal phosphate composite material is in the above range, so that the electrochemical performance of the lithium ion secondary battery is better.

[0007] In any embodiment, the coating layer comprises a first coating layer, and the first coating layer is located on the surface of the primary microparticles. In the embodiment, the first coating layer comprises a carbon-containing material, and the first coating layer is located on the surface of the primary microparticles, so that the carbon-containing material of the first coating layer on the surface of the primary microparticles of the lithium-containing transition metal phosphate composite material can continuously adsorb the manganese ions dissolved from the spinel structure lithium manganate.

[0008] In any embodiment, the coating layer further comprises a second coating layer, and the second coating layer is located on the surface of the secondary particles. The second coating layer comprises a carbon-containing material, so that the carbon-containing material in the lithium-containing transition metal phosphate composite material is uniformly and densely coated on the surface of the lithium-containing transition metal phosphate, which is beneficial to control the contact angle A1 of the lithium-containing transition metal phosphate composite material with water and the contact angle A2 of the spinel structure lithium manganate with water to be more close, and is beneficial to improve the film forming performance of the positive active material layer of the positive electrode sheet.

[0009] In any embodiment, the mass fraction of the carbon element in the lithium-containing transition metal phosphate composite material is 0.85%-1.9% based on the total mass of the lithium-containing transition metal phosphate composite material. In the embodiment, the content of the carbon element coated on the surface of the lithium-containing transition metal phosphate composite material in the range can effectively improve the hydrophobicity of the lithium-containing transition metal phosphate, and further reduce the difference in the contact angle between the lithium-containing transition metal phosphate composite material and the spinel structure lithium manganate. In the embodiment, the content of the carbon element coated on the surface of the lithium-containing transition metal phosphate composite material in the range makes the coating layer be uniformly coated on the surface of the lithium-containing transition metal phosphate, and the coating layer is relatively complete, and the thickness of the coating layer on the surface of the lithium-containing transition metal phosphate is better.

[0010] In any embodiment, the lithium transition metal phosphate composite material has a spherical or near-spherical shape. In the implementation method of this application, compared to lithium transition metal phosphate composite materials with blocky or other shapes, the spherical or near-spherical shape of the lithium transition metal phosphate composite material has a larger specific surface area, resulting in a larger surface energy. This leads to a smaller difference in the contact angle between the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide with water, ultimately resulting in better dispersibility of the slurry when lithium transition metal phosphate and spinel-structured lithium manganese oxide are mixed together. In the embodiments of this application, when spherical or near-spherical materials are packed with spherical particles, the contact area between particles is small, which can reduce agglomeration and particle bridging phenomena, resulting in fewer voids between particles and a higher bulk density. Therefore, the spherical or near-spherical shape of the lithium transition metal phosphate composite material can increase the packing density of the positive electrode sheet.

[0011] Among them, quasi-spherical refers to a structure on the surface of lithium-containing transition metal phosphate composite materials that has at least a partially curved surface.

[0012] In any embodiment, lithium-containing transition metal phosphates include those with the structural formula Li x Fe y M z P a O b The material, wherein M includes any one or more of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb, with 0.05≤x≤1.2, 0.2≤y≤1, 0≤z≤0.8, 0.9≤a≤1, and 3.5≤b≤4. In the embodiments of this application, the lithium-containing transition metal phosphate includes materials with the chemical formula Li... x Fe y M z P a O b The material, lithium-containing transition metal phosphate, has an olivine structure and can provide lithium ions to the positive electrode, which is beneficial to improving the specific capacity of the positive electrode. Furthermore, doping with metal elements such as M can improve the electrochemical performance of the olivine-structured lithium-containing transition metal phosphate composite material.

[0013] In any embodiment, the volume average particle size (DV50) of the spinel-structured lithium manganese oxide is 8 μm-17 μm. In the embodiments of this application, the spinel-structured lithium manganese oxide is a particulate material with a volume average particle size (DV50) within the above range, resulting in better electrochemical performance of the lithium-ion secondary battery.

[0014] In any embodiment, spinel-structured manganate includes structures with the formula Li e Mn 2-s Ms O d The material, wherein 0.95 < e ≤ 1.2, 0 ≤ s ≤ 0.5, 3.5 ≤ d ≤ 4, and M includes one or more of Ni, V, Tc, Co, Ni, Mg, Fe, Al, Zn, Ca, Zr, Y, Nb, Mo, Cr, and W. In the embodiments of this application, the spinel-structured lithium manganese oxide includes materials with the structural formula Li e Mn 2-s M s O d The materials used result in better electrochemical performance of lithium-ion secondary batteries.

[0015] In any embodiment, the resistivity of the positive electrode is less than or equal to 0.77 Ω·m. In the embodiments of this application, the resistivity of the positive electrode being less than or equal to 0.77 Ω·m enables the positive electrode to have a faster electron transport speed during charging and discharging.

[0016] A second aspect of this application provides a method for preparing a secondary lithium-ion battery, comprising providing a positive electrode slurry, the positive electrode slurry comprising a lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide, the lithium transition metal phosphate composite material comprising a lithium transition metal phosphate and a coating layer disposed on the surface of the lithium transition metal phosphate, the coating layer comprising a carbon-containing material. The contact angle between the lithium transition metal phosphate composite material and water is A1, and the contact angle between the spinel-structured lithium manganese oxide and water is A2, the ratio of A1 to A2 being 0.8-1.2; coating the positive electrode slurry onto a current collector, drying it to obtain a positive electrode sheet with a positive electrode active material layer; and stacking the positive electrode sheet, a separator, and a negative electrode sheet to form a lithium-ion secondary battery.

[0017] In this embodiment, the ratio of the contact angles between the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide with water is controlled between 0.8 and 1.2, so that the attraction or repulsion forces of the two materials to the same solvent or other substances are similar. Therefore, when the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide are mixed together to prepare a slurry, the attraction and repulsion forces of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide to the solvent, conductive agent, and other substances in the slurry are similar, so that the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide can be uniformly dispersed in the slurry, improving the processability of the slurry. After the positive electrode material is coated on the current collector and dried, the surface flatness of the positive electrode sheet is better, and the conductivity of the positive electrode sheet is better. The lithium-ion secondary battery assembled from this positive electrode sheet, separator, and negative electrode sheet has good electrochemical performance.

[0018] In any embodiment, the preparation of the lithium transition metal phosphate composite material includes mixing a lithium transition metal phosphate precursor, a lithium salt precursor, and a first carbon source, and obtaining an intermediate product through spray drying and a first sintering. The intermediate product is then mixed with a second carbon source, and a second sintering is performed to form the lithium transition metal phosphate composite material. The lithium transition metal phosphate composite material includes a lithium transition metal phosphate and a coating layer, the coating layer being disposed on the surface of the lithium transition metal phosphate, and the coating layer comprising a carbon-containing material. In this embodiment, mixing the lithium transition metal phosphate precursor, the lithium salt precursor, and the first carbon source, and spray drying can produce a mist with small and uniform particle size. The mist is then dried to form small and uniform particles, which are then sintered to obtain the intermediate product. The intermediate product is mixed with the second carbon source and subjected to a second sintering to finally prepare the lithium transition metal phosphate composite material with a carbon-coated surface. In this embodiment, the carbon material is coated twice onto the surface of lithium transition metal phosphate particles. This improves the uniformity of the carbon material coating on the lithium transition metal phosphate surface, making the surface tension of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide more similar. Consequently, the contact angle of the lithium transition metal phosphate composite material is similar to that of the spinel-structured lithium manganese oxide, improving the processability of the slurry prepared by mixing the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide. Simultaneously, the carbon material coating layer on the surface of the formed lithium transition metal phosphate composite material adsorbs Mn dissolved from the spinel-structured lithium manganese oxide. 2+ Ions have a better effect.

[0019] In any embodiment, the spray drying temperature is 260℃-320℃, and / or the outlet air temperature is 85℃-98℃, and / or the atomizer frequency is 20Hz-80Hz. In the embodiments of this application, the spray drying temperature of 260℃-320℃, and / or the outlet air temperature of 85℃-95℃, and / or the atomizer frequency of 20Hz-80Hz can give the lithium transition metal phosphate composite material a better spherical or near-spherical structure, and make the lithium transition metal phosphate composite material particles more uniform, with good uniformity of primary microparticles. It can also improve the surface structure of the material, and make it easier to control the volume average particle size (DV50) of the secondary particles of the lithium transition metal phosphate composite material, thereby improving the electrochemical performance of the positive electrode sheet in the lithium-ion secondary battery.

[0020] In any embodiment, the temperature of the first sintering is 700℃-800℃, and the time of the first sintering is 6h-20h. By controlling the temperature and time of the first sintering within the above range, it is beneficial to control the volume average particle size DV50 of the secondary particles and the average particle size of the primary particles of the lithium transition metal phosphate composite material within a better range.

[0021] In any embodiment, the slurry prepared by mixing lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide has a viscosity of less than or equal to 25,000 mPa·s after standing for 8 hours. The fact that the slurry viscosity remains below 25,000 mPa·s after 8 hours of standing demonstrates that the slurry still possesses good fluidity and stability, resulting in good continuity of slurry coating during the application process.

[0022] A third aspect of this application provides an electrical device comprising a lithium-ion secondary battery of the first aspect and / or a method for preparing a lithium-ion secondary battery of the second aspect. The lithium-ion secondary battery in the embodiments of this application possesses at least the same advantages as the lithium-ion secondary battery of the first aspect, and / or at least the same advantages as the lithium-ion secondary battery prepared by the method for preparing a lithium-ion secondary battery of the second aspect. Attached Figure Description

[0023] Figure 1 This is a structural schematic diagram of a vehicle according to one embodiment of this application;

[0024] Figure 2 This is an exploded structural diagram of a lithium-ion secondary battery according to one embodiment of this application.

[0025] Figure 3 This is an exploded structural diagram of a battery cell according to one embodiment of this application.

[0026] Figure 4 This is a scanning electron microscope image of a lithium transition metal phosphate composite material according to an embodiment of this application;

[0027] Figure 5 This is a contact angle test diagram of a lithium transition metal phosphate composite material according to an embodiment of this application;

[0028] Figure 6 This is a comparison chart of viscosity tests of one embodiment of this application and a pair of proportions of slurry after standing for 8 hours. Detailed Implementation

[0029] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0030] 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 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 "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" 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.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0035] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0036] Spinel-structured lithium manganese oxide has been widely studied due to its advantages such as environmentally friendly raw materials, low cost, simple processing, and high safety. However, during charging and discharging, transition metal ions dissolve from the spinel-structured lithium manganese oxide and deposit on the negative electrode, causing continuous decomposition of the solid electrolyte interphase (SEI) film on the negative electrode surface. This continuously consumes lithium ions in the battery system, leading to capacity decay. Related technologies use lithium-containing transition metal phosphates to coat the spinel-structured lithium manganese oxide, avoiding direct contact between the spinel-structured lithium manganese oxide and the electrolyte. However, due to the lattice mismatch between the two materials, it is difficult for the lithium-containing transition metal phosphates to be uniformly distributed on the surface of the spinel-structured lithium manganese oxide. Furthermore, the lithium-containing transition metal phosphates are prone to detachment during the slurry preparation process, resulting in poor slurry processing performance when the two materials are combined, posing significant challenges to the slurry preparation process.

[0037] When lithium-containing transition metal phosphates and spinel-structured lithium manganese oxide are mixed as positive electrode active materials with the same solvent, the positive electrode active materials tend to agglomerate, resulting in a gel-like state in the slurry. The lithium-containing transition metal phosphates or spinel-structured lithium manganese oxide cannot be uniformly and persistently dispersed in the slurry, leading to poor slurry processing performance. The resulting slurry exhibits poor film-forming performance when coated on the current collector, resulting in uneven distribution of the positive electrode active material and poor conductivity in the prepared positive electrode sheet. Therefore, the first aspect of this application provides a technical solution: a lithium-ion secondary battery including a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive current collector and a positive electrode active material layer disposed on the positive current collector. The positive electrode active material layer includes a lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide. The lithium-containing transition metal phosphate composite material includes a lithium-containing transition metal phosphate and a coating layer, with the coating layer disposed on the surface of the lithium-containing transition metal phosphate and including a carbon-containing material. The contact angle between the lithium-containing transition metal phosphate composite material and water is A1, and the contact angle between the spinel structure lithium manganese oxide and water is A2. The ratio of A1 to A2 is 0.8-1.2.

[0038] In this embodiment, the lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide. Because the lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide have different chemical bonds, they have different surface energies. The difference in surface energy between the lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide can be reflected by the ratio of their contact angles with the same solvent. By controlling the contact angle ratio between the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide with water to be between 0.8 and 1.2, the attractive or repulsive forces of the two materials to the same solvent or other substances are similar. This ensures that when the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide are mixed together to prepare a slurry, the attractive and repulsive forces of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide to the solvent, conductive agent, and other substances in the slurry are similar, allowing for uniform dispersion of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide in the slurry. This reduces the phenomenon of particle agglomeration in the slurry when the lithium transition metal phosphate composite material, spinel-structured lithium manganese oxide, and conductive agent are mixed together, thus solving the problems of uneven mixing of lithium transition metal phosphate composite material, spinel-structured lithium manganese oxide, and conductive agent, which ultimately leads to uneven positive electrode sheets, poor film formation performance, and poor conductivity, affecting the specific capacity and lifespan of lithium-ion secondary batteries. In the manufacturing process of the lithium-ion secondary battery described in this application, the dispersibility of lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide during slurry preparation can be improved, thereby enhancing the processability of the slurry containing lithium-containing transition metal phosphate and spinel-structured lithium manganese oxide. In this application embodiment, a mixture of lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide is used to prepare the active material layer. This allows the carbon-containing material coating layer on the surface of the lithium-containing transition metal phosphate to adsorb the carbon coating on the surface of the lithium-containing transition metal phosphate particles, which in turn adsorbs the Mn dissolved from the spinel-structured lithium manganese oxide. 2+ Ions, thereby reducing Mn 2+ The amount of ion deposition on the negative electrode improves Mn 2+ Damage to the SEI film on the negative electrode improves the stability of lithium-ion secondary batteries and reduces Mn. 2+ The amount of electrolyte reaching the lithium-ion secondary battery reduces Mn 2+ Side reactions occur with the electrolyte, thereby improving the capacity and lifespan of lithium-ion secondary batteries. In the embodiments of this application, by coating the surface of lithium-containing transition metal phosphate with carbon-containing material, the specific surface area of ​​the carbon-containing material is increased, resulting in better adsorption performance of manganese ions dissolved from spinel-structured lithium manganese oxide.

[0039] In this embodiment, a carbon-containing material is coated onto the surface of a lithium transition metal phosphate. The carbon-containing materials on the surface of the lithium transition metal phosphate are connected by carbon-carbon nonpolar covalent bonds, while the lithium transition metal phosphate particles have phosphorus-oxygen polar covalent bonds. Therefore, after coating the surface of the lithium transition metal phosphate with carbon material, the chemical bonds on the surface of the lithium transition metal phosphate are changed, thereby changing the surface energy of the lithium transition metal phosphate. This makes the water repulsion of the lithium transition metal phosphate stronger after being coated with carbon material, thus reducing the difference in surface energy between the lithium transition metal phosphate and the spinel structure lithium manganese oxide.

[0040] In any embodiment, the lithium-containing transition metal phosphate composite material includes secondary particles, which are formed by the agglomeration of primary microparticles. The volume average particle size (DV50) of the secondary particles is 4 μm-10 μm, and the average particle size of the primary microparticles is 100 nm-2000 nm. In this embodiment, the average particle size of the primary microparticles is relatively small, ranging from 100 nm to 2000 nm. Therefore, the secondary particles formed by the agglomeration of primary microparticles have a larger specific surface area. A larger specific surface area is beneficial for improving the lithium-ion transport rate, thereby improving the electrochemical performance of the lithium-ion secondary battery. In this embodiment, the volume average particle size (DV50) of the secondary particles and the average particle size of the primary microparticles of the lithium-containing transition metal phosphate composite material are within the above-mentioned ranges, resulting in better electrochemical performance of the lithium-ion secondary battery. The volume average particle size (DV50) of the secondary particles in the lithium transition metal phosphate composite material can be 4 μm, 6 μm, 8 μm, 10 μm, or any range formed by any two of the above values, such as 4 μm-6 μm, 6 μm-8 μm, 8 μm-10 μm, etc. The average particle size of the primary microparticles can be 100 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, or any range formed by any two of the above values, such as 100 nm-500 nm, 500 nm-1000 nm, 1000 nm-1500 nm, 1500 nm-2000 nm, etc.

[0041] The average particle size of the primary microparticles is common knowledge in the field and has a common meaning in the field. It can be measured by methods and instruments in the field.

[0042] Among them, the volume average particle size DV50 of secondary particles is common knowledge in the field and has a common meaning in the field. It can be measured by methods and instruments in the field.

[0043] In any embodiment, the coating layer includes a first coating layer located on the surface of the primary microparticles. In this embodiment, the first coating layer comprises a carbon-containing material, and this first coating layer is located on the surface of the primary microparticles, allowing the carbon-containing material of the first coating layer on the surface of the primary particles of the lithium transition metal phosphate composite material to continuously adsorb manganese ions dissolved from the spinel-structured lithium manganese oxide structure. In this embodiment, the primary microparticles are coated with a first coating layer, so that during the charging and discharging process of the lithium-ion secondary battery, as the charging and discharging proceeds, the spinel-structured lithium manganese oxide secondary particles may break down. This breakage exposes more reaction sites with the electrolyte, allowing Mn dissolved from the spinel-structured lithium manganese oxide to be released. 2+ More will be added, and at this point, the first coating layer on the surface of the microparticles can still effectively adsorb the Mn dissolved from the spinel-structured lithium manganese oxide. 2+ This results in high cycle stability of lithium-ion secondary batteries.

[0044] In any embodiment, the coating layer further includes a second coating layer located on the surface of the secondary particles. The second coating layer includes a carbon-containing material, which ensures that the carbon-containing material in the lithium transition metal phosphate composite material is uniformly and densely coated on the surface of the lithium transition metal phosphate. This is beneficial for controlling the contact angle A1 between the lithium transition metal phosphate composite material and water to be closer to the contact angle A2 between the spinel structure lithium manganese oxide and water, thereby improving the film-forming performance of the positive electrode active material layer of the positive electrode sheet.

[0045] In any embodiment, based on the total mass of the lithium-containing transition metal phosphate composite material, the mass percentage of carbon in the lithium-containing transition metal phosphate composite material is 0.85%-1.9%. In the embodiments of this application, the carbon content coated on the surface of the lithium-containing transition metal phosphate composite material within this range can effectively adsorb Mn dissolved from spinel-structured lithium manganese oxide. 2+ Furthermore, it can effectively improve the hydrophobicity of lithium-containing transition metal phosphates, thereby reducing the difference in contact angle between the lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide. In the embodiments of this application, the carbon content of the lithium-containing transition metal phosphate composite material surface coating is within this range, so that the coating layer can be uniformly coated on the surface of the lithium-containing transition metal phosphate, and the coating layer is relatively complete, with a better thickness of the coating layer on the surface of the lithium-containing transition metal phosphate. The mass percentage of carbon in the lithium-containing transition metal phosphate composite material can be 0.85%, 1.15%, 1.4%, 1.65%, 1.9%, etc., or a range consisting of any two of the above values, such as 0.85%-1.15%, 1.15%-1.4%, 1.4%-1.65%, 1.65%-1.9%, etc.

[0046] In any embodiment, the lithium transition metal phosphate composite material has a spherical or near-spherical shape. In the implementation method of this application, compared to lithium transition metal phosphate composite materials with blocky or other shapes, the spherical or near-spherical shape of the lithium transition metal phosphate composite material has a larger specific surface area, thereby allowing the lithium transition metal phosphate composite material to have a larger surface energy. This reduces the difference in contact angle between the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide and water, ultimately resulting in better dispersibility of the slurry when lithium transition metal phosphate and spinel-structured lithium manganese oxide are combined. In the embodiments of this application, when spherical or near-spherical materials are packed with spherical particles, the contact area between particles is small, which can reduce agglomeration and particle bridging phenomena, resulting in fewer voids between particles and a higher bulk density. Therefore, the spherical or near-spherical shape of the lithium transition metal phosphate composite material can increase the packing density of the positive electrode sheet.

[0047] Among them, quasi-spherical refers to a structure on the surface of lithium-containing transition metal phosphate composite materials that has at least a partially curved surface.

[0048] In any application method, the matrix includes structures with the formula Li x Fe y M z P a O b The material, wherein M includes any one or more of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb, with 0.05≤x≤1.2, 0.2≤y≤1, 0≤z≤0.8, 0.9≤a≤1, and 3.5≤b≤4. In the embodiments of this application, the lithium-containing transition metal phosphate includes materials with the chemical formula Li... x Fe y M z P a O b The material, a lithium transition metal phosphate, has an olivine structure. Lithium transition metal phosphates can provide lithium ions to the positive electrode, which is beneficial for improving the specific capacity of the positive electrode. Doping with metal elements such as M can improve the electrochemical performance of the olivine-structured lithium transition metal phosphate positive electrode active material. Optionally, in this application embodiment, the M element includes manganese, that is, the lithium transition metal phosphate includes lithium iron phosphate or lithium manganese iron phosphate, where the value of z can be 0, 0.2, 0.4, 0.6, 0.8, etc., or a range consisting of any two of the above values, for example, 0≤z≤0.2, 0.2≤z≤0.4, 0.4≤z≤0.6, 0.6≤z≤0.8, etc.

[0049] In any embodiment, the volume average particle size (DV50) of spinel-structured lithium manganese oxide is 8 μm-17 μm. In the embodiments of this application, the volume average particle size (DV50) of spinel-structured lithium manganese oxide is within the above range, resulting in better electrochemical performance of the lithium-ion secondary battery. The volume average particle size (DV50) of spinel-structured lithium manganese oxide can be 8 μm, 10 μm, 13 μm, 15 μm, 17 μm, etc., or a range formed by any two of the above values, such as 8 μm-10 μm, 10 μm-13 μm, 13 μm-15 μm, 15 μm-17 μm, etc.

[0050] Different particle sizes of the same substance will result in different surface energies. Different particle sizes lead to different specific surface areas, and the number of atoms and molecules per unit surface area also differs, thus resulting in different surface energies. The volume average particle size (DV50) of lithium transition metal phosphate composite particles is in the range of 4 μm-10 μm. In the embodiments of this application, the volume average particle size (DV50) of spinel-structured lithium manganese oxide particles is in the range of 8 μm-17 μm. This allows the surface energies of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide to be similar, thereby exhibiting similar attractive or repulsive forces towards the same substance. When the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide are mixed to prepare a slurry, the dispersibility of the two active materials and other additives in the solvent can be improved.

[0051] In any application method, spinel-structured lithium manganese oxide includes those with the structural formula Li e Mn 2-s M s O d The material, wherein 0.95 < e ≤ 1.2, 0 ≤ s ≤ 0.5, 3.5 ≤ d ≤ 4, and M includes one or more of Ni, V, Tc, Co, Ni, Mg, Fe, Al, Zn, Ca, Zr, Y, Nb, Mo, Cr, and W. In the embodiments of this application, the spinel-structured lithium manganese oxide includes materials with the structural formula Li e Mn 2-s M s O d The material is selected to make the positive electrode active material have better electrochemical performance. The value of s can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range consisting of any two of the above values, such as 0≤z≤0.1, 0.1≤z≤0.2, 0.2≤z≤0.3, 0.3≤z≤0.4, 0.4≤z≤0.5, etc.

[0052] In any embodiment, the resistivity of the positive electrode sheet per unit area is less than or equal to 0.77 Ω·m. In the embodiments of this application, a resistivity of less than or equal to 0.77 Ω·m for the positive electrode sheet allows for faster electron transport during charging and discharging, thereby resulting in a higher power density for the lithium-ion secondary battery. Specifically, the resistivity of the positive electrode sheet can be even lower, such as 0.70 Ω·m, 0.58 Ω·m, or 0.51 Ω·m.

[0053] A second aspect of this application provides a method for preparing a secondary lithium-ion battery, comprising providing a positive electrode slurry, the positive electrode slurry comprising a lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide, the lithium transition metal phosphate composite material comprising a lithium transition metal phosphate and a coating layer disposed on the surface of the lithium transition metal phosphate, the coating layer comprising a carbon-containing material. The contact angle between the lithium transition metal phosphate composite material and water is A1, and the contact angle between the spinel-structured lithium manganese oxide and water is A2, the ratio of A1 to A2 being 0.8-1.2. The positive electrode slurry is coated onto a current collector and dried to obtain a positive electrode sheet with a positive electrode active material layer. The positive electrode sheet, a separator, and a negative electrode sheet are stacked to form a lithium-ion secondary battery.

[0054] In this embodiment, the ratio of the contact angles between the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide with water is controlled between 0.8 and 1.2, so that the attraction or repulsion forces of the two materials to the same solvent or other substances are similar. Therefore, when preparing a slurry by combining the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide, the attraction and repulsion forces of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide to the solvent, conductive agent, and other substances in the slurry are similar, ensuring uniform dispersion of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide in the slurry and improving the processability of the slurry. After coating the positive electrode material onto the current collector and drying, the surface flatness of the positive electrode sheet is better, and the conductivity of the positive electrode sheet is better. The lithium-ion secondary battery assembled from this positive electrode sheet, separator, and negative electrode sheet has good electrochemical performance. The contact angle ratio between the lithium-containing transition metal phosphate composite material and the spinel-structured lithium manganese oxide can be 0.8, 0.9, 1.0, 1.1, 1.2, etc., or any range formed by any two of the above values, such as 0.8-0.9, 0.9-1.0, 1.0-1.1, 1.1-1.2, etc.

[0055] In any embodiment, the positive electrode comprises a lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide. The weight ratio of the two materials is (1:9) to (7:3). A suitable weight ratio of lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide allows for better coordination between the lithium-containing transition metal phosphate composite material particles and the spinel-structured lithium manganese oxide particles, effectively suppressing the dissolution of manganese ions into the negative electrode, while simultaneously enabling the positive electrode to have a high energy density. The weight ratio of the lithium-containing transition metal phosphate composite material to the spinel-structured lithium manganese oxide can be 1:9, 1, 13:9, 17:9, 7:3, etc., or a range formed by any two of the above values, such as (1:9)-(1), (1)-(13:9), (13:9)-(17:9), (17:9)-(7:3), etc.

[0056] In any embodiment, the preparation of the lithium transition metal phosphate composite material includes mixing a lithium transition metal phosphate precursor, a lithium salt precursor, and a first carbon source, and obtaining an intermediate product through spray drying and a first sintering. The intermediate product is then mixed with a second carbon source, and a second sintering is performed to form the lithium transition metal phosphate composite material. This composite material includes a lithium transition metal phosphate and a coating layer, the coating layer being disposed on the surface of the lithium transition metal phosphate and comprising a carbon-containing material. In this embodiment, mixing the lithium transition metal phosphate precursor, the lithium salt precursor, and the first carbon source, followed by spray drying, produces a fine and uniform mist. This mist is then dried to form fine and uniform particles, which are then sintered to obtain the intermediate product. The intermediate product is mixed with the second carbon source and subjected to a second sintering to finally prepare a lithium transition metal phosphate composite material with a carbon-coated surface. In this embodiment, the carbon material is coated twice onto the surface of lithium transition metal phosphate particles. This improves the uniformity of the carbon material coating on the lithium transition metal phosphate surface, making the surface tension of the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide more similar. The contact angle of the resulting lithium transition metal phosphate composite material is similar to that of spinel-structured lithium manganese oxide, thus improving the processability of the slurry prepared by mixing the lithium transition metal phosphate composite material and spinel-structured lithium manganese oxide. Simultaneously, the carbon material coating layer on the surface of the formed lithium transition metal phosphate adsorbs Mn dissolved from the spinel-structured lithium manganese oxide. 2+ Ions have a better effect.

[0057] In this embodiment, the first carbon source includes one or more of polyethylene glycol, glucose, sucrose, or starch. The second carbon source includes one or more of methanol, ethanol, or ethylene glycol. These are merely examples, and this application does not limit the specific types of the first and second carbon sources.

[0058] In some embodiments of this application, an intermediate product is obtained by mixing a lithium-containing transition metal phosphate precursor, a lithium salt precursor, and a first carbon source, followed by spray drying and a first sintering. This includes mixing a lithium-containing transition metal phosphate precursor, a lithium salt precursor, a first carbon source, and a dopant, followed by spray drying and sintering to obtain the intermediate product. The dopant comprises one or more of Ni, V, Tc, Co, Ni, Mg, Fe, Al, Zn, Ca, Zr, Y, Nb, Mo, Cr, and W.

[0059] In the embodiments of this application, the lithium-containing transition metal phosphate in the lithium-containing transition metal phosphate composite material is selected from lithium iron phosphate and / or iron manganese phosphate. The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium chloride.

[0060] In this embodiment, the temperature of the first sintering is 700℃-800℃, and the sintering time is 6h-20h. By controlling the temperature and time of the first sintering within the above range, it is beneficial to control the volume average particle size (DV50) of the secondary particles and the average particle size of the primary particles in the lithium transition metal phosphate composite material within a preferred range. The temperature of the first sintering can be 700℃, 750℃, 780℃, 800℃, or any range formed by any two of the above values, such as 700℃-750℃, 750℃-780℃, 780℃-800℃, etc. The sintering time of the first sintering can be 6h, 9h, 13h, 16h, 20h, or any range formed by any two of the above values, such as 6h-9h, 9h-13h, 13h-16h, 16h-20h, etc.

[0061] In this embodiment, the second sintering temperature is 600℃-980℃, and the second sintering time is 8-20h. By controlling the temperature and time of the second sintering within the above range, the obtained lithium transition metal phosphate composite material has a better structure, a more complete crystal structure, and a better particle size of the secondary particles. The second sintering temperature can be 600℃, 700℃, 800℃, 900℃, 980℃, or any range formed by any two of the above values, such as 600℃-700℃, 700℃-800℃, 800℃-900℃, 900℃-980℃, etc. The second sintering time can be 8h, 10h, 13h, 16h, 20h, or any range formed by any two of the above values, such as 8h-13h, 13h-16h, 16h-20h, etc.

[0062] In any embodiment, the preparation of spinel-structured lithium manganese oxide includes using a manganese source and a lithium salt as precursors, and sintering the precursors in an oxygen or air atmosphere. The manganese source for the spinel-structured lithium manganese oxide includes one or more of manganese dioxide, manganese tetroxide, manganese carbonate, manganese sulfate, and manganese oxalate; preferably, manganese dioxide or manganese tetroxide is selected. The lithium salt for the spinel-structured lithium manganese oxide includes one or more of lithium carbonate, lithium hydroxide, lithium nitrate, and lithium chloride.

[0063] In any application method, the spray drying spray temperature is 260℃-320℃, and / or the outlet air temperature is 85℃-98℃, and / or the atomizer frequency is 20Hz-80Hz. In the embodiments of this application, the spray drying spray temperature of 260℃-320℃, and / or the outlet air temperature of 85℃-98℃, and / or the atomizer frequency of 20Hz-80Hz can give the lithium transition metal phosphate composite material a better spherical or near-spherical structure, and make the lithium transition metal phosphate composite material particles more uniform, with good uniformity of primary microparticles. It can also improve the surface structure of the material, and make it easier to control the volume average particle size (DV50) of the secondary particles of the lithium transition metal phosphate composite material, thereby improving the electrochemical performance of lithium-ion secondary batteries. The spray drying temperature can be 260℃, 280℃, 300℃, 320℃, or any range formed by any two of the above values, such as 260℃-280℃, 280℃-300℃, 300℃-320℃, etc. The outlet air temperature can be 85℃, 90℃, 95℃, 98℃, or any range formed by any two of the above values, such as 85℃-90℃, 90℃-95℃, 95℃-98℃, etc. The atomizer frequency can be 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, or any range formed by any two of the above values, such as 20Hz-30Hz, 30Hz-40Hz, 40Hz-50Hz, 50Hz-60Hz, 60Hz-70Hz, 70Hz-80Hz, etc.

[0064] In this embodiment, the slurry prepared by mixing lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide has a viscosity of less than or equal to 25,000 mPa·s after standing for 8 hours. The fact that the slurry viscosity remains below 25,000 mPa·s after 8 hours of standing demonstrates that the slurry still possesses good fluidity and stability, resulting in good continuity of slurry coating during the application process.

[0065] A third aspect of this application provides an electrical device comprising a lithium-ion secondary battery of the first aspect and / or a method for preparing a lithium-ion secondary battery of the second aspect. The lithium-ion secondary battery of this application embodiment possesses at least the same advantages as the lithium-ion secondary battery of the first aspect, and / or at least the same advantages as the lithium-ion secondary battery prepared by the method for preparing a lithium-ion secondary battery of the second aspect.

[0066] The batteries disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, and spacecraft. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; spacecraft can include airplanes, rockets, space shuttles, and spacecraft.

[0067] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0068] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A lithium-ion secondary battery 100 is installed inside the vehicle 1000. The battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The lithium-ion secondary battery 100 can be used to power the vehicle 1000; for example, it can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the lithium-ion secondary battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0069] In some embodiments of this application, the lithium-ion secondary battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0070] Please refer to Figure 2 , Figure 2This is an exploded structural diagram of a battery 100 provided in some embodiments of this application. The lithium-ion secondary battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0071] In the lithium-ion secondary battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the casing 10. Alternatively, the lithium-ion secondary battery 100 can also consist of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple lithium-ion secondary battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the casing 10. The lithium-ion secondary battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20. The battery cells 20 can be cylindrical, flat, cuboid, or other shapes.

[0072] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. The battery cell 20 refers to the smallest unit that makes up a battery. Figure 3 The battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0073] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, allowing battery cell 20 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with cell assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0074] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the cell assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the cell assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0075] The cell assembly 23 is the component in the battery cell 100 where the electrochemical reaction occurs. The casing 22 may contain one or more cell assemblies 23. The cell assembly 23 is mainly formed by winding or stacking positive and negative electrode plates, and typically a separator is provided between the positive and negative electrode plates. The portions of the positive and negative electrode plates containing active material constitute the main body of the cell assembly, while the portions of the positive and negative electrode plates without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals to form a current loop.

[0076] Typically, a lithium-ion secondary battery 100 includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0077] [Positive electrode plate]

[0078] In some embodiments, the positive electrode includes a positive current collector, and a layer of positive active material is disposed on at least one surface of the positive current collector.

[0079] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0080] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0081] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0082] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0083] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as lithium transition metal phosphate composite material and spinel structure lithium manganese oxide, conductive agent, binder and any other components in a solvent (e.g. N-methylpyrrolidone), to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0084] [Negative electrode plate]

[0085] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0086] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0087] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0088] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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 batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0089] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0090] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0092] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0093] [Isolation membrane]

[0094] In some embodiments, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0095] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. 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.

[0096] [Electrolytes]

[0097] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0098] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0099] 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.

[0100] 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.

[0101] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into a battery cell assembly using a winding or stacking process.

[0102] In some embodiments, the housing 22 may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

[0103] This application does not impose any particular restrictions on the shape of the battery cell 20, which can be cylindrical, square or other arbitrary shapes.

[0104] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0105] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0106] Example 1

[0107] Preparation of positive electrode active materials

[0108] 1) Preparation of lithium-containing transition metal phosphate composite materials:

[0109] 1762g of ferrous sulfate heptahydrate, 235g of lithium carbonate, 730g of ammonium dihydrogen phosphate, and 11.54g of polyethylene glycol were mixed evenly in acetone, and then spray-dried to form granules. The spray drying temperature was 260℃, the outlet air temperature was 95℃, and the atomizer frequency was 50Hz. The mixture was sintered at 750℃ (the temperature of the first sintering) for 10 hours in a nitrogen atmosphere to obtain an intermediate product, which was lithium iron phosphate coated with dot-like carbon-containing material. The primary carbon source was polyethylene glycol, with an average molecular weight of 3600-4400, and the carbon content of the intermediate product was approximately 0.84%.

[0110] A second carbon source is sprayed onto the intermediate product using a high-speed mixer equipped with a spraying device. The product is then sintered in a nitrogen atmosphere at 750°C (the temperature of the second sintering) for 5 hours to obtain a lithium-containing transition metal phosphate composite material. This composite material is a relatively dense carbon-containing material coated with lithium iron phosphate (carbon content of 1.2%). The second carbon source is a liquid carbon source, specifically ethanol. In this embodiment, the lithium-containing transition metal phosphate composite material includes secondary particles with a volume average particle size (DV50) of 7 μm, and primary microparticles with an average particle size of 0.1 μm.

[0111] 2) Preparation of spinel-structured lithium manganese oxide:

[0112] Lithium carbonate, manganese tetroxide (with a volume average particle size DV50 of 13 μm), aluminum oxide, and lithium fluoride were mixed evenly according to the molar ratio of Li, Mn, Al, and F of 1.03:1.8:0.2:0.05. The mixture was then sintered at 850℃ for 12 h in a sintering furnace. After mechanical crushing, spherical spinel-structured lithium manganese oxide with a volume average particle size Dv50 of approximately 13 μm was obtained.

[0113] Preparation of the positive electrode sheet

[0114] Lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide were used as positive electrode active materials. The volume average particle size (DV50) of the lithium-containing transition metal phosphate composite material was 7 μm, and that of the spinel-structured lithium manganese oxide was 13 μm. The lithium-containing transition metal phosphate composite material, spinel-structured lithium manganese oxide, conductive carbon black (super-P), carbon nanotubes (CNTs), and PVDF were mixed uniformly in a mass ratio of 28.5:66.5:1.5:0.5:3. N-methylpyrrolidone (NMP) was added as a solvent to adjust the solid content to 70%-80%. After stirring evenly, a positive electrode slurry was obtained. This slurry was coated on both sides of a 13 μm Al foil, and then vacuum dried at 120℃, cold-pressed, and cut into strips to obtain the positive electrode sheet.

[0115] Preparation of the negative electrode sheet

[0116] Graphite, acetylene black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) are mixed in a mass ratio of 95:2:2:1. Deionized water is added to adjust the solid content to 45%-55%. After stirring evenly, a negative electrode slurry is obtained. Then, it is coated, dried, cold-pressed, and slit to form a negative electrode sheet.

[0117] Preparation of Electrolyte

[0118] In an argon-atmospheric glove box, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a mass ratio of 35:65 to obtain a solvent. LiPF6 was then added and dissolved in the solvent, and the mixture was stirred evenly to obtain a 1 mol / L LiPF6 electrolyte.

[0119] [Septum]

[0120] A 7μm polyethylene membrane with a double-sided 2μm CCS ceramic coating was used as the separator.

[0121] [Battery Manufacturing]

[0122] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the cathode and negative electrode to provide isolation. These are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with prepared electrolyte, and undergoes processes such as encapsulation, electrolyte injection, formation, and venting to obtain a lithium-ion battery.

[0123] Example 2

[0124] The difference from Example 1 is as follows: In the preparation of the positive electrode active material, the frequency of the atomizer during the preparation of the lithium transition metal phosphate composite material is 65 Hz; the obtained lithium transition metal phosphate composite material includes secondary particles with a volume average particle size (DV50) of 4 μm, and primary microparticles with an average particle size of 0.1 μm. During the preparation of the positive electrode sheet, the volume average particle size (DV50) of the secondary particles in the lithium transition metal phosphate composite material is 4 μm. Other aspects are similar to Example 1 and will not be repeated here.

[0125] Example 3

[0126] The difference from Example 1 is as follows: In the preparation of the positive electrode active material, the frequency of the atomizer is 30Hz during the preparation of the lithium transition metal phosphate composite material; the lithium transition metal phosphate composite material includes secondary particles with a volume average particle size (DV50) of 10 μm, and primary microparticles with an average particle size of 0.1 μm. During the preparation of the positive electrode sheet, the volume average particle size (DV50) of the secondary particles in the lithium transition metal phosphate composite material is 10 μm. Other aspects are similar to Example 1 and will not be repeated here.

[0127] Example 4

[0128] The difference from Example 1 is as follows: In the preparation of the positive electrode active material, during the preparation of spinel-structured lithium manganese oxide, the volume average particle size (DV50) of manganese tetroxide is 5 μm; the resulting spinel-structured lithium manganese oxide has a volume average particle size (DV50) of 8 μm. During the preparation of the positive electrode sheet, the volume average particle size (DV50) of the spinel-structured lithium manganese oxide is 8 μm. Other aspects are similar to Example 1 and will not be repeated here.

[0129] Example 5

[0130] The difference from Example 1 is as follows: In the preparation of the positive electrode active material, during the preparation of spinel-structured lithium manganese oxide, the volume average particle size (DV5) of manganese tetroxide is 11 μm; the resulting spinel-structured lithium manganese oxide has a volume average particle size (DV50) of 17 μm. During the preparation of the positive electrode sheet, the volume average particle size (DV50) of the spinel-structured lithium manganese oxide is 17 μm. Other aspects are similar to Example 1 and will not be repeated here.

[0131] Example 6

[0132] The difference from Example 1 is as follows: In the preparation of the positive electrode active material, the first sintering temperature in the preparation of the lithium transition metal phosphate composite material is 710℃; the obtained lithium transition metal phosphate composite material includes secondary particles with a volume average particle size (DV50) of 4 μm, and primary microparticles with an average particle size of 0.07 μm; in the preparation of the positive electrode sheet, the volume average particle size (DV50) of the secondary particles in the lithium transition metal phosphate composite material is 4 μm, and the average particle size of the primary microparticles is 0.07 μm. Other aspects are similar to Example 1 and will not be repeated here.

[0133] Comparative Example 1

[0134] The difference from Example 1 is that, in the preparation of the positive electrode active material, the first sintering temperature of the lithium transition metal phosphate composite material is 660°C; the lithium transition metal phosphate composite material includes secondary particles with a volume average particle size DV50 of 2 μm, and the secondary particles include primary microparticles with an average particle size of 0.01 μm; in the preparation of the positive electrode sheet, the volume average particle size DV50 of the secondary particles of the lithium transition metal phosphate composite material is 2 μm, and the average particle size of the primary microparticles is 0.1 μm.

[0135] Comparative Example 2

[0136] The difference from Example 1 lies in the preparation of the positive electrode active material. During the preparation of the lithium transition metal phosphate composite material, the first sintering temperature is 820°C. The lithium transition metal phosphate composite material includes secondary particles with a volume average particle size (DV50) of 7 μm, and primary microparticles with an average particle size of 3 μm. In the preparation of the positive electrode sheet, the secondary particles of the lithium transition metal phosphate composite material have a volume average particle size (DV50) of 7 μm, and the primary microparticles have an average particle size of 3 μm.

[0137] The specific testing methods for the relevant parameters in the above embodiments and comparative examples are as follows:

[0138] 1. Contact angle measurement

[0139] Test subjects: Lithium-containing transition metal phosphate composite materials and spinel-structured lithium manganese oxide were used as positive electrode active materials to prepare positive electrode sheets.

[0140] (1) Prepare a slurry with a mass ratio of positive electrode active material, conductive agent super-P, CNT and PVDF of 95:1.5:0.5:3, coat it on 13μm Al foil, cut it into 3cm×3cm square pieces, and blow the electrode pieces with a hair dryer to remove dust.

[0141] (2) Prepare the test liquid: Fill the liquid dosing syringe with deionized water and fix the liquid dosing syringe on the contact angle tester. The equipment model is SDC-200S, voltage is AC220V, power is 150W, and frequency is 50 / 60HZ. Slightly turn the liquid dosing knob and push the liquid dosing syringe until the first drop of liquid is dripped out to remove the air.

[0142] (3) Place the sample: Place the positive electrode flat on the measurement platform, adjust the three-dimensional position and the spotlight, so that the sample is in a suitable position on the detection screen.

[0143] (4) Set the test mode: Set the volume of the water droplet to 10μL, the measurement mode to dynamic mode, and collect an image every 50ms.

[0144] (5) Start the test: Click the start button and observe the test process and results.

[0145] (6) Contact angle fitting: Select a 500ms image after the droplet comes into contact with the electrode for fitting. Select ellipse as the fitting mode. The contact angle is obtained after fitting.

[0146] 2. Viscosity test

[0147] Test subject: A slurry was prepared by mixing lithium-containing transition metal phosphate composite material, spinel-structured lithium manganese oxide, conductive agent, and binder, and allowed to stand for 8 hours. Specifically, the slurry was prepared by mixing lithium-containing transition metal phosphate composite material, spinel-structured lithium manganese oxide, conductive carbon black (super-P), carbon nanotubes (CNT), and PVDF in a mass ratio of 28.5:66.5:1.5:0.5:3 and allowed to stand for 8 hours.

[0148] Using an NDJ-5S rotational viscometer, 4 # The rotor was measured with a range of 50,000 mPa·s.

[0149] Test procedure: Fix rotor #4 on the rotational viscometer, adjust the height until the slurry completely submerges the rotor groove, rotate at 12 rpm, 25°C, start the test and record the viscosity value after about 30 seconds.

[0150] 3. Diaphragm resistance test

[0151] The positive electrode sheets prepared in each embodiment were cut into 50mm×50mm squares and placed flat on the probe. The probe diameter was 15mm. The equipment was started, the pressure was set to 0.395-0.405T, and the data was recorded after holding the pressure for 10s.

[0152] 4. Primary particle size test

[0153] Particle size was measured using scanning electron microscopy (SEM). The SEM used was a Philips XL30. The method was as follows: the sample was placed on the SEM stage and the scanning range was 100 nm to 2 μm. The scale was used to mark the size of the particles in one measurement. The average particle size in one measurement was calculated as the sum of the particle sizes of all measured particles / the sum of the number of all measured particles.

[0154] 5. Volume average particle size DV50 test

[0155] Equipment Model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer; Reference Standard Procedure: GB / T19077-2016 / ISO 13320:2009; Specific Test Procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% opacity), add 20ml of deionized water, and sonicate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the sample. Then, measure the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0156] 6. Electrochemical performance testing

[0157] 1) Gram capacity test

[0158] After assembling the above positive and negative electrode sheets into a coin cell, let it stand for 120 minutes, and then charge it to 4.3V at a constant current of 0.1C under a constant temperature environment of 25°C. Then charge it at a constant voltage of 4.3V until the current drops to 0.05C, and then discharge it to 2.8V at a constant current of 0.33C to obtain the first discharge capacity.

[0159] 2) Cyclic performance test

[0160] A lithium-ion rechargeable battery was charged at a constant current of 0.33C to 4.3V under a constant temperature environment of 25℃, then charged at a constant voltage of 4.3V until the current dropped to 0.05C, and finally discharged at a constant current of 0.33C to 2.8V. This initial discharge capacity (C0) was obtained. This charge-discharge cycle was repeated until the 500th cycle, and the discharge capacity after 500 cycles was obtained, denoted as C. n .

[0161] Capacity retention rate = discharge capacity after 500 cycles (C) n ) / First-cycle discharge capacity (C0).

[0162]

[0163] like Figure 4 The image shown is a scanning electron microscope image of the lithium-containing transition metal phosphate composite material prepared in Example 1 of this application. As can be seen from the image, the lithium-containing transition metal phosphate composite material of Example 1 of this application consists of spherical secondary particles. Figure 5 The image shows the contact angle diagram of the lithium transition metal phosphate composite material of Example 1 of this application. From... Figure 5 As shown in Table 1, when the volume average particle size of the spinel-structured lithium manganese oxide remains constant, as the volume average particle size (DV50) of the secondary particles in the lithium transition metal phosphate composite material gradually increases, the contact angle between the lithium transition metal phosphate composite material and water gradually increases. The ratio of the contact angle between the lithium transition metal phosphate composite material and water to the contact angle between the spinel-structured manganese oxide and water shows a trend of first increasing and then decreasing, with the ratio in Example 1 being closest to 1. This indicates that the difference in contact angle between the lithium transition metal phosphate composite material and the spinel-structured lithium manganese oxide can be reduced by controlling the volume average particle size (DV50) of the secondary particles. Figure 6The figure shows a comparison of viscosity tests (8h) between Example 1 and Comparative Example 1 of this application. As can be seen from the figure, the viscosity of the slurry prepared in Example 1 continuously increases over time, reaching 9850 mPa·s after 8 hours of standing. The viscosity of Comparative Example 1 after 8 hours of standing is 30350 mPa·s. The viscosity of Example 1 after 8 hours of standing is approximately one-third that of Comparative Example 1, indicating that the slurry prepared in Example 1 has better stability compared to Comparative Example 1. This demonstrates that the lithium-containing transition metal phosphate composite material of Example 1 of this application has a smaller contact angle difference with the spinel-structured lithium manganese oxide, resulting in a lower 8-hour viscosity of the slurry. The prepared slurry exhibits better processing performance, is easier to form films, and is easier to prepare the positive electrode active material layer. The slurry viscosity of Comparative Examples 1 and 2 is as high as 27314 mPa·s-30350 mPa·s at 8h, which is not conducive to the industrial production of lithium-ion secondary batteries and makes it difficult to form a film. If the slurry of Comparative Examples 1 and 2 is made into a positive electrode sheet under laboratory conditions, the resistivity of the obtained positive electrode sheet is relatively large. The resistivity of the positive electrode sheet prepared in Examples 1-6 of this application is relatively small.

[0164] Table 1 shows the process and performance parameters of the positive electrode active materials in each embodiment and comparative example. Compared with Comparative Examples 1 and 2, the contact angle ratio of the two positive electrode active materials in Examples 1-6 of this application is within 0.8-1.2, and the contact angle ratio of the lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide with water is closer to 1, indicating that the difference in contact angle between the two positive electrode active materials in Examples 1-6 of this application is smaller. Compared with Comparative Examples 1 and 2, the viscosity of the slurry prepared by the composite of the two positive electrode active materials in Examples 1-6 of this application also decreased significantly after standing for 8 hours, indicating that the processability of the slurry prepared by the composite of the two materials can be improved by controlling the volume average particle size DV50 of the carbon-coated lithium-containing transition metal phosphate composite material and spinel-structured lithium manganese oxide. Meanwhile, compared with Comparative Examples 1 and 2, the resistance of the positive electrode film in Examples 1-6 of this application also decreased significantly. This is because the two positive electrode active materials are within a suitable range of volume average particle size, which can reduce the phenomenon of particle agglomeration when the two materials are combined to prepare the slurry. Therefore, the active materials and conductive agents in the slurry are more uniformly dispersed, resulting in better conductivity of the positive electrode sheet.

[0165] Furthermore, as can be seen from Examples 1, 2, and 3, when the volume average particle size of the spinel-structured lithium manganese oxide remains constant and the volume average particle size of the lithium transition metal phosphate composite material gradually increases, the contact angle difference between the lithium transition metal phosphate composite material and the spinel-structured lithium manganese oxide shows a trend of first decreasing and then increasing. The contact angle difference between the two materials is minimal when the volume average particle size of the lithium transition metal phosphate composite material is 7 μm. In addition, in Example 1, the lithium-ion secondary battery assembled from the positive electrode sheet prepared by the lithium transition metal phosphate composite material with a DV50 of 7 μm and the spinel-structured lithium manganese oxide with a DV50 of 13 μm exhibits good specific capacity and capacity retention.

[0166] The above are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A lithium-ion secondary battery, characterized in that, include: Positive electrode, negative electrode, and electrolyte; The positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector, wherein the positive active material layer includes a lithium-containing transition metal phosphate composite material and spinel structure lithium manganese oxide. The lithium-containing transition metal phosphate composite material includes a lithium-containing transition metal phosphate and a coating layer, wherein the coating layer is disposed on the surface of the lithium-containing transition metal phosphate, and the coating layer includes a carbon-containing material; The contact angle between the lithium-containing transition metal phosphate composite material and water is A1, and the contact angle between the spinel-structured lithium manganese oxide and water is A2. The ratio of A1 to A2 is 0.8-1.

2.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The lithium-containing transition metal phosphate composite material includes secondary particles, which in turn include primary microparticles; the volume average particle size (DV50) of the secondary particles is 4 μm-10 μm, and the average particle size of the primary microparticles is 100 nm-2000 nm.

3. The lithium-ion secondary battery according to claim 2, characterized in that, The coating layer includes a first coating layer located on the surface of the primary microparticles, and the first coating layer includes a carbon-containing material.

4. The lithium-ion secondary battery according to claim 3, characterized in that, The coating layer further includes a second coating layer located on the surface of the secondary particles, and the second coating layer includes a carbon-containing material.

5. The lithium-ion secondary battery according to any one of claims 1-4, characterized in that, Based on the total mass of the lithium-containing transition metal phosphate composite material, the mass percentage of carbon in the lithium-containing transition metal phosphate composite material is 0.85%-1.9%.

6. The lithium-ion secondary battery according to any one of claims 1-5, characterized in that, The lithium-containing transition metal phosphate composite material can be spherical or near-spherical in shape.

7. The lithium-ion secondary battery according to any one of claims 1-6, characterized in that, The lithium-containing transition metal phosphate includes the structural formula Li x Fe y M z P a O b The material, wherein M includes any one or more of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B and Nb, 0.05≤x≤1.2, 0.2≤y≤1, 0≤z≤0.8, 0.9≤a≤1, 3.5≤b≤4.

8. The lithium-ion secondary battery according to any one of claims 1-7, characterized in that, The spinel-structured lithium manganese oxide has a volume average particle size (DV50) of 8 μm-17 μm.

9. The lithium-ion secondary battery according to any one of claims 1-8, characterized in that, The spinel-structured lithium manganese oxide includes the structural formula Li. e Mn 2-s M s O d The material is provided, wherein 0.6 < e ≤ 1.2, 0 ≤ s ≤ 0.5, and 3.5 ≤ d ≤ 4; M includes one or more of Ni, V, Tc, Co, Ni, Mg, Fe, Al, Zn, Ca, Zr, Y, Nb, Mo, Cr, and W.

10. The lithium-ion secondary battery according to any one of claims 1-9, characterized in that, The resistivity of the positive electrode is less than or equal to 0.77 Ω·m.

11. A method for preparing a lithium-ion secondary battery, characterized in that, include: A positive electrode slurry is provided, the positive electrode slurry comprising a lithium-containing transition metal phosphate composite material and a spinel-structured lithium manganese oxide, the lithium-containing transition metal phosphate composite material comprising a lithium-containing transition metal phosphate and a coating layer disposed on the surface of the lithium-containing transition metal phosphate, the coating layer comprising a carbon-containing material; the contact angle between the lithium-containing transition metal phosphate composite material and water is A1, the contact angle between the spinel-structured lithium manganese oxide and water is A2, and the ratio of A1 to A2 is 0.8-1.2; The positive electrode slurry is coated onto the current collector and dried to obtain a positive electrode sheet with a positive electrode active material layer. The positive electrode, separator, and negative electrode are stacked to form a lithium-ion battery.

12. The method for preparing a lithium-ion secondary battery according to claim 11, characterized in that, The preparation of the lithium-containing transition metal phosphate composite material includes: An intermediate product was obtained by mixing a lithium-containing transition metal phosphate precursor, a lithium salt, and a first carbon source, followed by spray drying and a first sintering. The intermediate product and the second carbon source are mixed and sintered a second time to form a lithium transition metal phosphate composite material. The lithium transition metal phosphate composite material includes a lithium transition metal phosphate and a coating layer. The coating layer is disposed on the surface of the lithium transition metal phosphate and includes a carbon-containing material.

13. The method for preparing a lithium-ion secondary battery according to claim 12, characterized in that, The spray drying process has an injection temperature of 260℃-320℃, and / or an outlet air temperature of 85℃-98℃, and / or an atomizer frequency of 20Hz-80Hz.

14. The method for preparing a lithium-ion secondary battery according to claim 12 or 13, characterized in that, The temperature of the first sintering is 700℃-800℃, and the time of the first sintering is 6h-20h.

15. The method for preparing a lithium-ion secondary battery according to any one of claims 11-14, characterized in that, The viscosity of the positive electrode slurry after standing for 8 hours is less than or equal to 25000 mPa·s.

16. An electrical appliance, characterized in that, This includes the lithium-ion secondary battery as described in any one of claims 1-10, or / and the method for preparing the lithium-ion secondary battery as described in any one of claims 11-15.

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