Lithium manganate composite, method for preparing the same, secondary battery, and electric device

Abstract

The application provides a lithium manganate composite material, a preparation method thereof, a secondary battery and an electric device. The lithium manganate composite material comprises core particles and a coating layer; the molecular formula of the core particles is Li 1+x Mn 2‑y M y O 4‑Z A z , in the molecular formula, -0.2≤x≤0.2, 0≤y≤0.1, 0≤Z≤0.1, M comprises one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr, Mo, Nb and Sn, and A comprises one or more of F, Cl and S; the coating layer is coated on at least part of the outer surface of the core particles, and the coating layer comprises an organic phosphonic acid or a salt thereof. The application can ensure the structural stability of the core particles and the cycle stability of the negative electrode active material, thereby further improving the capacity performance, storage performance and cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a lithium manganese oxide composite material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Secondary batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] As batteries are used in a wider range of applications, the requirements for the performance of rechargeable batteries are becoming increasingly stringent. To improve the performance of rechargeable batteries, the materials within them, such as the positive electrode active material, are typically optimized and improved.

[0004] However, even with the improved positive electrode active materials currently used in secondary batteries, the batteries still cannot simultaneously improve both cycle performance and storage performance during use. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide a lithium manganese oxide composite material, a method for preparing the same, a secondary battery, and an electrical device thereof.

[0006] The first aspect of this application provides a lithium manganese oxide composite material for secondary batteries, the lithium manganese oxide composite material comprising core particles and a coating layer; the molecular formula of the core particles is Li. 1+x Mn 2-y M y O 4-Z A z In the molecular formula, -0.2≤x≤0.2, 0≤y≤0.1, 0≤Z≤0.1, M includes one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr, Mo, Nb and Sn, and A includes one or more of F, Cl and S; the coating layer covers at least a portion of the outer surface of the core particle, and the coating layer includes an organophosphonic acid or its salt.

[0007] Therefore, the coating layer containing organophosphonic acid or its salts, as described in this application, is disposed on the outer surface of the core particle, which can isolate at least a portion of the core particle from the electrolyte, thereby reducing the risk of side reactions occurring when the electrolyte and the core particle come into contact. This reduces the risk of electrolyte corrosion causing damage to the core particle, thus providing good protection for the core particle and ensuring its structural stability. Organophosphonic acid or its salts readily react with hydrofluoric acid (HF) in the electrolyte, reducing the corrosive effect of HF on the core particle, thereby reducing the dissolution of transition metals such as manganese in the core particle. The amount of manganese migrating from the electrolyte to the negative electrode active material is significantly reduced, and the SEI film on the surface of the negative electrode active material is less likely to be damaged. The SEI film provides good protection for the negative electrode active material, ensuring its cycle stability, thereby further improving the capacity performance, storage performance, and cycle performance of the secondary battery.

[0008] In any embodiment, the organophosphonic acid or its salts include phosphonic acid groups, the number of which is denoted as n, where 2 ≤ n ≤ 4; alternatively, 2 ≤ n ≤ 3.

[0009] Therefore, when the organophosphonic acid or its salts contain the above-mentioned number of phosphonic acid groups, the ability to stabilize manganese can be further improved; and the acidity of the organophosphonic acid or its salts will not be too high, so as not to damage the core particles.

[0010] In any embodiment, the organophosphonic acid or its salts include one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, hydroxyethylidene diphosphonic acid, aminoethylidene diphosphonic acid, methylaminedimethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, hydroxypropylidene diphosphonic acid, aminopropylphosphonic acid, potassium hexamethylenediaminetetramethylenephosphonate, sodium hydroxyethylidene diphosphonate, potassium hydroxyethylidene diphosphonate, nitrosotrimethylenephosphonic acid, and iminodimethylidene phosphonic acid.

[0011] In any embodiment, the coating layer covers the outer surface of the nucleus in a continuous, layered manner. The coating layer provides sufficient protection for the nucleus, isolating it from the electrolyte and reducing the risk of electrolyte corrosion, thereby ensuring the cycling stability of the nucleus.

[0012] In any embodiment, the coating layer includes a first region portion and a second region portion that are connected to each other; the average thickness of the first region portion is denoted as H1nm, the average thickness of the second region portion is denoted as H2nm, and the lithium manganese oxide composite material satisfies: 1

[0013] ​Therefore, the average thickness of the first region and the second region of this application are different, with the average thickness of the first region being greater than that of the second region. The different average thicknesses of the different regions of the coating layer can reduce the impedance of the coating layer while ensuring protection of the nucleus particles, thereby improving the kinetic performance of the secondary battery. Furthermore, this structure of the coating layer can also reduce the risk of the nucleus particles reacting with hydrofluoric acid (HF) in the electrolyte, further improving the kinetic performance of the secondary battery.

[0014] In any embodiment, the coating rate of the coating layer is denoted as S%, which is the percentage of the total area of ​​the coating layer to the outer surface area of ​​the core particle; the lithium manganese oxide composite material satisfies: 50≤S≤95; optionally, 50≤S≤80.

[0015] Therefore, when the coating rate S% is within the above range, the coating layer can cover most of the outer surface of the core particle, thus providing sufficient protection for the core particle; and the coating layer has relatively low impedance, so the impedance of lithium ions migrating from the core particle to the negative electrode active material during the charging and discharging process of the secondary battery is small, and the impedance of lithium ions migrating from the negative electrode active material to the core particle is small, thereby improving the dynamic performance of the secondary battery.

[0016] In any embodiment, based on the total mass of the lithium manganese oxide composite material, the mass percentage of the coating layer is denoted as P%. The lithium manganese oxide composite material satisfies: 0.01≤P≤5; optionally, 0.1≤P≤2.

[0017] Therefore, when the lithium manganese oxide composite material of this application meets the above-mentioned range, the coating layer can provide sufficient protection for the core particles and ensure the smooth migration of lithium ions, thereby ensuring the kinetic performance of the secondary battery.

[0018] In any embodiment, the core particles satisfy: -0.1≤x≤1.5, 0.001≤y≤0.06, 0.001≤z≤0.05; and / or M includes one or more of Mg, Al, and Sn, and A includes F and / or S. The core particles and coating layer of the above molecular formula work together, with the coating layer providing sufficient protection for the core particles, and the core particles providing a higher specific capacity for the secondary battery, thereby improving the battery's capacity utilization.

[0019] In any embodiment, the pH value of the lithium manganese oxide composite material satisfies: 6 ≤ pH ≤ 8; optionally, 6.5 ≤ pH ≤ 7.5.

[0020] When the pH value of the lithium manganese oxide composite material is within the above range, on the one hand, the pH value will not be too high, which can reduce the risk of gel formation on the surface of the lithium manganese oxide composite material, thereby ensuring the smooth migration of lithium ions and improving the kinetic performance of the secondary battery; on the other hand, the pH value will not be too low, which can reduce the damage to the core particles and ensure the cycle stability of the core particles, thereby improving the cycle stability of the secondary battery.

[0021] In any embodiment, the specific surface area of ​​the lithium manganese oxide composite material is denoted as BET g / cm³. 3 , BET≤1.

[0022] Therefore, when the specific surface area of ​​the lithium manganese oxide composite material of this application meets the above-mentioned range, the contact area between the lithium manganese oxide composite material and the electrolyte is relatively small, which can reduce the contact interface between the lithium manganese oxide composite material and the electrolyte, thereby reducing the risk of side reactions at the interface. The manganese in the core particles is not easily dissolved, which can ensure the overall structural stability of the lithium manganese oxide composite material, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0023] A second aspect of this application also provides a method for preparing a lithium manganese oxide composite material, the method comprising: S100, providing a solvent and a coating material comprising an organophosphonic acid or a salt thereof, and mixing the solvent and the coating material to form a coating slurry; S200, supplying the coating slurry to a core particle, such that the coating slurry is cured on at least a portion of the outer surface of the core particle to form a coating layer, thereby preparing a lithium manganese oxide composite material, wherein the core particle has the molecular formula Li. 1+x Mn 2-y M y O 4-Z A z In the molecular formula, -0.2≤x≤0.2, 0≤y≤0.1, 0≤Z≤0.1, M includes one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr and Sn, and A includes one or more of F, Cl and S.

[0024] Therefore, the preparation method of this application is simple, and the prepared coating layer can fully protect the core particles and reduce the dissolution of transition metals in the core particles. Thus, when the prepared lithium manganese oxide composite material is applied to a secondary battery, it can improve the capacity performance, cycle performance and storage performance of the secondary battery.

[0025] In any embodiment, the solvent includes one or more of water, ethanol, and methanol.

[0026] Therefore, this application can control the morphology of the coating layer by selecting the solvent. The morphology of the coating layer can include the thickness of the coating layer, for example, forming films of different thicknesses in different regions of the coating layer.

[0027] In any embodiment, the mass ratio of solvent to coating material is denoted as Q, where 0 < Q ≤ 0.1; and / or the mass ratio of solvent to core particle is denoted as N, where 0 < N ≤ 0.7. When the mass ratio Q of solvent to coating material satisfies the above range, the solvent can fully dissolve the coating material, which is more conducive to the coating material coating the surface of the core particle. When the mass ratio N of solvent to core particle satisfies the above range, the amount of solvent used can fully dissolve the coating material, coating the core particle surface with the coating material, and the solvent evaporation process is conducive to forming a coating layer of uneven thickness on the surface of the core particle, which is beneficial to further improving the kinetic performance of the secondary battery.

[0028] In any embodiment, the curing temperature is 80°C to 120°C.

[0029] Therefore, the curing temperature of this application is relatively low, which will not damage the coating layer and core particles while the solvent evaporates, thus ensuring the overall structural stability of the lithium manganese oxide composite material and thus ensuring the cycle stability of the lithium manganese oxide composite material when it is used in secondary batteries.

[0030] A third aspect of this application also provides a secondary battery, which includes a positive electrode, comprising a lithium manganese oxide composite material as described in any embodiment of the first aspect of this application or a lithium manganese oxide composite material obtained by any method described in any embodiment of the second aspect of this application.

[0031] The fourth aspect of this application also provides an electrical device, including a secondary battery as described in the third aspect of this application. Attached Figure Description

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

[0033] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0034] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0035] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0036] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0037] Figure 5 yes Figure 4An exploded view of an embodiment of the battery pack shown.

[0038] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0039] The accompanying drawings may not be drawn to scale.

[0040] The annotations in the attached figures are explained as follows:

[0041] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0042] 5. Secondary battery; 51. Housing; 52. Electrode assembly;

[0043] 53. Cover plate;

[0044] 6. Electrical appliances. Detailed Implementation

[0045] The following detailed description discloses embodiments of the positive electrode active material, secondary battery, and power-consuming 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0046] 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.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0048] 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.

[0049] 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.

[0050] 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).

[0051] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0052] As the lithium intercalation compound and the provider of active lithium ions, the stability of the positive electrode active material's structure directly affects the overall performance of lithium-ion batteries. Trace amounts of moisture in the electrolyte can easily react with lithium salts such as LiPF6 to form hydrofluoric acid (HF). The presence of HF makes the positive electrode active material prone to side reactions, leading to the dissolution of transition metals from the positive electrode active material into the electrolyte. This dissolution can damage the positive electrode active material and, when it migrates to the negative electrode active material, it may damage the solid electrolyte interface (SEI) film on the surface of the negative electrode active material. This puts the structure of the negative electrode active material at risk of being destroyed, thus deteriorating the capacity, storage, and cycle performance of the secondary battery. Taking lithium manganese oxide as an example, HF in the electrolyte causes lithium manganese oxide to undergo a disproportionation reaction to generate Mn.2+ On the one hand, the disproportionation reaction causes changes in the lattice of lithium manganese oxide; on the other hand, Mn 2+ Mn is reduced to metallic Mn on the surface of the negative electrode active material, catalytically decomposes the SEI film, destroys the interface of the negative electrode active material, and may also block the lithium intercalation channels of the negative electrode active material. Mn may even be deposited on the interface between the negative electrode current collector and the negative electrode active material, causing delamination between the layers. All of the above factors may lead to capacity decay of the secondary battery, and the storage performance and cycle performance of the secondary battery will deteriorate.

[0053] In view of the above problems, the inventors considered ensuring the structural stability of the positive electrode active material, such as lithium manganese oxide, from the perspective of protecting the positive electrode active material. The inventors deposited a coating layer on the surface of the positive electrode active material, such as lithium manganese oxide, which contains an organophosphonic acid or its salt. This coating layer provides good protection for the positive electrode active material and facilitates the formation of a good cathode electrolyte interface (CEI) film, further protecting the positive electrode active material and thus improving the capacity performance, storage performance, and cycle performance of the secondary battery. The technical solution for the positive electrode active material will be described in detail below.

[0054] Lithium manganese oxide composite materials

[0055] In a first aspect, this application proposes a lithium manganese oxide composite material, which comprises core particles and a coating layer, wherein the molecular formula of the core particles is Li. 1+x Mn 2-y M y O 4-Z A z In the molecular formula, -0.2≤x≤0.2, 0≤y≤0.1, 0≤Z≤0.1, M includes one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr, Mo, Nb and Sn, and A includes one or more of F, Cl and S; the coating layer covers at least a portion of the outer surface of the core particle, and the coating layer includes an organophosphonic acid or its salt.

[0056] Organophosphonic acids are compounds in which the phosphorus atom in one or more phosphonic acid groups is directly bonded to a carbon atom. Organophosphonates are compounds in which the hydrogen atom in the phosphonic acid group of an organophosphonic acid is replaced by a metal cation.

[0057] Although the mechanism is not fully understood, the lithium manganese oxide composite material of this application can improve the capacity performance, storage performance, and cycle performance of secondary batteries when applied to them; the inventors speculate that the reasons may be as follows:

[0058] A coating layer containing organophosphonic acid or its salts is disposed on the outer surface of the core particle, which can isolate at least a portion of the core particle from the electrolyte, thereby reducing the risk of side reactions occurring when the electrolyte and the core particle come into contact. This reduces the risk of electrolyte corrosion causing damage to the core particle, thus providing good protection for the core particle and ensuring its structural stability. The inventors speculate that the coating layer containing organophosphonic acid or its salts may also promote the formation of a CEI film on the surface of the lithium manganese oxide composite material. The CEI film can further protect the lithium manganese oxide composite material as a whole. During the charging and discharging process of the secondary battery, the CEI film remains dense and stable, thus providing continuous protection for the lithium manganese oxide composite material, thereby further ensuring the structural stability of the lithium manganese oxide composite material. When lithium manganese oxide composite material is used in secondary batteries, it can improve the capacity performance, storage performance, and cycle performance of the secondary battery.

[0059] Organophosphonic acids or their salts readily react with hydrofluoric acid (HF) in the electrolyte, reducing the corrosive effect of HF on the core particles. This reduces the dissolution of transition metals such as manganese from the core particles, significantly decreasing the amount of manganese migrating from the electrolyte to the negative electrode active material. Consequently, the SEI film on the surface of the negative electrode active material is less likely to be damaged. The SEI film provides excellent protection for the negative electrode active material, ensuring its cycle stability. This further improves the capacity, storage, and cycle performance of the secondary battery.

[0060] Organophosphonic acids or their salts may undergo complexation reactions with transition metals such as manganese, thereby stabilizing manganese on the core particles and reducing the risk of manganese dissolving into the electrolyte, thus further improving the capacity performance, storage performance and cycle performance of secondary batteries.

[0061] In some embodiments, the organophosphonic acid or its salts include phosphonic acid groups, the number of which is denoted as n, where 2 ≤ n ≤ 4.

[0062] The inventors hypothesize that when organophosphonic acids or their salts contain the aforementioned number of phosphonic acid groups, their ability to stabilize manganese can be further enhanced; and the acidity of the organophosphonic acids or their salts will not be too high, thus not damaging the nucleus particles. Optionally, 2 ≤ n ≤ 3; for example, n can be 2, 3, or 4.

[0063] As an example, organophosphonic acids or their salts may include one or more of the following: aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, hydroxyethylidene diphosphonic acid, aminoethylidene diphosphonic acid, methylaminedimethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, hydroxypropylidene diphosphonic acid, aminopropylphosphonic acid, potassium hexamethylenediaminetetramethylenephosphonate, sodium hydroxyethylidene diphosphonate, potassium hydroxyethylidene diphosphonate, nitrosotrimethylenephosphonic acid, and iminodimethylidene phosphonic acid.

[0064] The aforementioned organophosphonic acids or their salts can provide good protection against nuclear particles, thereby ensuring the cycle stability of lithium manganese oxide composite materials.

[0065] The coating layer can be applied to the core particles in various structural forms. In some embodiments, the coating layer is continuously layered on the outer surface of the core particles. The coating layer provides sufficient protection for the core particles, isolating them from the electrolyte and reducing the risk of electrolyte corrosion, thereby ensuring the cycling stability of the core particles. In other embodiments, the coating layer can also be discretely distributed in a layered manner on the outer surface of the core particles. The organophosphonic acid or its salt in the coating layer can stabilize the manganese in the core particles, reducing manganese dissolution into the electrolyte, thus ensuring the cycling stability of the core particles.

[0066] In some embodiments, the coating layer includes a first region portion and a second region portion connected to each other, the average thickness of the first region portion is denoted as H1 nm, the average thickness of the second region portion is denoted as H2 nm, and the lithium manganese oxide composite material satisfies 1 < H1 / H2 ≤ 3.

[0067] The average thickness of the first region and the second region differs, with the average thickness of the first region being greater than that of the second region. This difference in average thickness across different regions of the coating layer reduces the impedance of the coating layer while ensuring protection of the nucleus particles, thereby improving the kinetic performance of the secondary battery. Furthermore, this structure of the coating layer reduces the risk of reaction between the nucleus particles and the hydrofluoric acid (HF) in the electrolyte, further improving the kinetic performance of the secondary battery. Optionally, 1.5 ≤ H1 / H2 ≤ 2.5; exemplaryly, H1 / H2 can be 1, 1.1, 1.5, 1.6, 1.8, 2, 2.5, 2.8, or 3; or a range consisting of any two of the above values.

[0068] Both the first and second regions are components of the coating layer, but there is no clear boundary between them; they form a continuous structure. During the preparation of the coating layer, the average thickness of the first and second regions can be adjusted by regulating process parameters such as the type or concentration of the solvent.

[0069] In some implementations, 5 ≤ H1 ≤ 45.

[0070] In this application, the average thickness of the first region can be measured using testing methods and instruments known in the art, specifically as follows: a transmission electron microscope (TEM) image of the first region can be obtained, and then the average thickness at multiple (e.g., more than 30) different locations on the TEM image can be measured, and the average value can be taken as the average thickness H1 of the first region.

[0071] In some implementations, 5 < H2 ≤ 15.

[0072] In this application, the average thickness of the second region can be measured using testing methods and instruments known in the art, specifically as follows: a TEM image of the second region can be obtained using a transmission electron microscope, and then the average thickness at multiple (e.g., more than 30) different locations on the TEM image can be measured, and the average value can be taken as the average thickness H2 of the second region.

[0073] In some implementations, the coverage ratio of the coating layer is denoted as S; the lithium manganese oxide composite material satisfies: 50≤S≤95.

[0074] When the coating coverage S% is within the above range, the coating layer can cover most of the outer surface of the core particle, thus providing sufficient protection for the core particle. Furthermore, the coating layer has relatively low impedance, resulting in lower impedance during the migration of lithium ions from the core particle to the negative electrode active material during the charging and discharging process of the secondary battery, and vice versa, thereby improving the kinetic performance of the secondary battery. Optionally, 50 ≤ S ≤ 80; for example, the coating coverage S% can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%; or any range of any two of the above values.

[0075] In this application, the coating ratio refers to the percentage of the total area of ​​the coating layer to the outer surface area of ​​the core particle; it can be detected using test methods and instruments known in the art, such as using a scanning electron microscope (SEM) to observe the microstructure of the lithium manganese oxide composite material and the core particle, thereby calculating the coating ratio.

[0076] In some implementations, the mass percentage of the coating layer is denoted as P based on the total mass of the lithium manganese oxide composite material, and the lithium manganese oxide composite material satisfies: 0.01≤P≤5.

[0077] When the lithium manganese oxide composite material meets the above range, the coating layer can provide sufficient protection for the core particles and ensure the smooth migration of lithium ions, thereby ensuring the kinetic performance of the secondary battery. Optionally, 0.1 ≤ P ≤ 2. For example, the mass percentage P% of the coating layer can be 0.01%, 0.02%, 0.05%, 0.08%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.50%, 0.80%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%; or a range consisting of any two of the above numerical ranges.

[0078] In some embodiments, the molecular formula of the nuclear particles is Li. 1+x Mn 2-y M y O 4-Z A z -0.1≤x≤1.5, 0.001≤y≤0.06, 0.001≤Z≤0.05; and / or M includes one or more of Mg, Al and Sn, and A includes F and / or S.

[0079] The core particles and coating layer of the above molecular formula work together. The coating layer can fully protect the core particles, and the core particles can provide a high specific capacity for the secondary battery, thereby improving the capacity performance of the secondary battery.

[0080] In some implementations, the pH value of the lithium manganese oxide composite material satisfies: 6 ≤ pH ≤ 8.

[0081] When the pH value of the lithium manganese oxide composite material is within the above-mentioned range, on the one hand, the pH value will not be too high, which can reduce the risk of gel formation on the surface of the lithium manganese oxide composite material, thereby ensuring the smooth migration of lithium ions and improving the kinetic performance of the secondary battery; on the other hand, the pH value will not be too low, which can reduce damage to the core particles and ensure the cycle stability of the core particles, thereby improving the cycle stability of the secondary battery. Optionally, 6.5 ≤ pH ≤ 7.5. For example, the pH value of the lithium manganese oxide composite material can be 6, 6.5, 7, 7.5 or 8; or within any two of the above values.

[0082] In this application, the pH value of the material has a meaning known in the art and can be tested using instruments and methods known in the art. For example, the material and solvent are added to an Erlenmeyer flask in a ratio of 1:9, stirred with a magnetic stirrer for 30 minutes, and allowed to stand for 1.5 hours after stirring. The pH value is then tested using a magnetic pH meter at an environment of 15-28°C and humidity ≤80%, and the average value of three tests is taken as the pH value of the material.

[0083] In some embodiments, the specific surface area of ​​the lithium manganese oxide composite material is denoted as BET g / cm³.3 , BET≤1.

[0084] When the specific surface area of ​​the lithium manganese oxide composite material meets the above-mentioned range, the contact area between the lithium manganese oxide composite material and the electrolyte is relatively small. This reduces the contact interface between the lithium manganese oxide composite material and the electrolyte, thereby lowering the risk of side reactions at the interface. Furthermore, the manganese in the core particles is less likely to dissolve, ensuring the overall structural stability of the lithium manganese oxide composite material, thus improving the kinetic and cycle performance of the secondary battery. For example, BET can be 1 g / cm³. 3 0.8 g / cm 3 0.6 g / cm 3 0.5 g / cm 3 0.4 g / cm 3 0.2 g / cm 3 Or 0.1 g / cm 3 Or it could be a range consisting of any two of the above values.

[0085] In this application, the specific surface area of ​​the material has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer-Emmett-Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0086] It should be noted that lithium manganese oxide composite materials can be used as positive electrode active materials in secondary batteries. The various parameter tests for lithium manganese oxide composite materials mentioned above can be conducted by sampling before coating or by sampling from the positive electrode film layer after cold pressing. When the lithium manganese oxide composite material test sample is taken from the positive electrode film layer after cold pressing, as an example, the sampling can be carried out as follows: arbitrarily select a cold-pressed positive electrode film layer and sample the lithium manganese oxide composite material (for example, a blade can be used to scrape the powder); place the collected lithium manganese oxide composite material powder in deionized water, then filter and dry it; then sinter the dried lithium manganese oxide composite material at a certain temperature and time (e.g., 400℃, 2h) to remove the binder and conductive agent, thus obtaining the test sample of the lithium manganese oxide composite material.

[0087] Method for preparing lithium manganese oxide composite materials

[0088] Secondly, this application proposes a method for preparing lithium manganese oxide composite materials. The method includes:

[0089] S100 provides a solvent and a coating material containing an organophosphonic acid or its salt, and mixes the solvent and the coating material into a coating slurry;

[0090] S200: A coating slurry is supplied to the core particles to cure the slurry on at least a portion of the outer surface of the core particles, forming a coating layer, thereby preparing a lithium manganese oxide composite material.

[0091] The molecular formula of the nuclear particle is Li. 1+x Mn 2-y M y O 4-Z A z In the molecular formula, -0.2≤x≤0.2, 0≤y≤0.1, 0≤Z≤0.1, M includes one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr and Sn, and A includes one or more of F, Cl and S.

[0092] The preparation method of this application is simple, and the prepared coating layer can fully protect the core particles and reduce the dissolution of transition metals in the core particles. As a result, when the prepared lithium manganese oxide composite material is applied to secondary batteries, it can improve the capacity performance, cycle performance and storage performance of secondary batteries.

[0093] The preparation method of this application can be used to prepare the lithium manganese oxide composite material of any embodiment of the first aspect of this application.

[0094] In some embodiments, the solvent includes one or more of water, ethanol, and methanol.

[0095] The morphology of the coating layer can be controlled by selecting the solvent. The morphology of the coating layer can include its thickness, for example, forming films of different thicknesses in different regions of the coating layer. Taking water as a solvent as an example, the coating material is dissolved in water and mixed, and then dried by means of vacuum filtration, pressure filtration, or centrifugation, thereby obtaining a coating layer with different thicknesses in different regions. For example, the coating layer includes a first region and a second region, with the thickness of the first region being greater than that of the second region. The inventors speculate that the reason for forming regions of different thicknesses in the coating layer is as follows: the solvation structure of the coating material in water, or the dissolution state of the coating material in water, may cause the aggregation state of the coating material on the surface of the core particle to be different during the evaporation of the solvent, thus resulting in different thicknesses of coating layers on different regions of the core particle surface. Furthermore, this application uses methods such as vacuum filtration, pressure, or centrifugation to dry the solvent, resulting in a lower content of residual solvent on the surface of the core particles. Consequently, during the solvent evaporation process, the coating material may not migrate to the surface of the core particles in a timely manner, meaning that the coating material is unevenly distributed on the surface of the core particles. This results in a thicker coating layer in some areas and a thinner coating layer in others on the surface of the core particles, which is beneficial for improving the kinetic performance of the secondary battery.

[0096] Of course, the solvent drying process of this application can also be carried out by direct heat treatment to evaporate the solvent; for example, the coating slurry is placed in a wet coating machine, and the solvent and coating material are stirred at 80~100°C in an inert non-oxidizing gas atmosphere, so that the coating material dissolves in the solvent and coats the core particles at the same time, the solvent can be evaporated, thereby forming a coating layer on the surface of the core particles.

[0097] In some embodiments, the mass ratio of solvent to coating material is denoted as Q, where 0 < Q ≤ 0.1.

[0098] When the mass ratio Q of the solvent to the coating material meets the above-mentioned range, the solvent can fully dissolve the coating material, which is more conducive to the coating material coating the surface of the core particle. For example, the mass ratio Q of the solvent to the coating material can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1; or a range of any two of the above values. In this application, Q can be the ratio of the mass percentage of the solvent to the mass percentage of the coating material, based on the total mass of the overall system composed of the solvent, coating material, and core particle.

[0099] The mass ratio of solvent to coating material can be considered as the ratio of the mass percentage of solvent to the mass percentage of coating material, based on the total mass of the coating material.

[0100] In some embodiments, the mass ratio of solvent to core particles is denoted as N, where 0 < N ≤ 0.7.

[0101] When the mass ratio N of solvent to core particles meets the above-mentioned range, the amount of solvent used is sufficient to dissolve the coating material, coating the surface of the core particles. Furthermore, the solvent evaporation process facilitates the formation of a coating layer of uneven thickness on the surface of the core particles, which is beneficial for further improving the kinetic performance of the secondary battery. For example, the mass ratio N of solvent to core particles can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, or 0.07; or any range of two of the above values. In this application, N can be the ratio of the mass percentage of solvent to the mass percentage of core particles, based on the total mass of the overall system composed of solvent, coating material, and core particles.

[0102] In some implementations, the curing temperature is 80°C to 120°C.

[0103] This application uses a low curing temperature, which, while evaporating the solvent, does not damage the coating layer or the core particles, thus ensuring the overall structural stability of the lithium manganese oxide composite material. This, in turn, guarantees the cycle stability of the lithium manganese oxide composite material when used in secondary batteries. For example, the curing temperature can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C; or a range of any two of the above values.

[0104] Secondary batteries

[0105] Thirdly, this application proposes a secondary battery.

[0106] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. A secondary battery includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes, primarily preventing short circuits between them while allowing metal ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts metal ions. The secondary battery described in this application can be a lithium-ion battery, a sodium-ion battery, etc., and particularly, a lithium-ion battery.

[0107] [Positive electrode plate]

[0108] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0109] In some embodiments, the positive electrode film layer includes a positive electrode active material, which is a lithium manganese oxide composite material prepared using the method of any embodiment of the first aspect of this application or any embodiment of the second aspect of this application. The positive electrode active material can significantly improve the performance of the secondary battery.

[0110] In some embodiments, the positive electrode active material may also be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0111] Specifically, the positive electrode active material can be a layered material, such as ternary materials, lithium nickel oxide / sodium materials, lithium cobalt oxide / sodium materials, lithium manganese oxide / sodium materials, lithium-rich / sodium layered materials, and rock salt phase layered materials; the general formula of the above materials is: Li x A y Ni a Co b Mn c M (1-a-b-c) Y z Where, 0≤x≤2.1, 0≤y≤2.1, and 0.9≤x+y≤2.1; 0≤a≤1, 0≤b≤1, 0≤c≤1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A is selected from one or more of Na, K, and Mg; M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y is selected from one or more of O and F.

[0112] The positive electrode active material can be an olivine-type phosphate active material, with the general formula: Li x A y Me a M b P 1-c X c Yz Where, 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A is selected from one or more of Na, K, and Mg; Me is selected from one or more of Mn, Fe, Co, and Ni; M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X is selected from one or more of S, Si, Cl, B, C, and N; Y is selected from one or more of O and F.

[0113] The positive electrode active material can be a spinel-structured positive electrode active material, such as lithium spinel manganese oxide, lithium spinel nickel manganese oxide, lithium-rich lithium spinel manganese oxide, and lithium nickel manganese oxide, etc., with the general formula: Li x A y Mn a M 2-a Y z Where 0≤x≤2, 0≤y≤1, and 0.9≤x+y≤2; 0.5≤a≤2; 3≤z≤5; A is selected from one or more of Na, K, and Mg; M is selected from one or more of Ni, Co, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y is selected from one or more of O and F.

[0114] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode film layer.

[0115] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode film layer.

[0116] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of the metal material include one or more combinations selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0117] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0118] [Negative electrode plate]

[0119] 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.

[0120] 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.

[0121] 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, lithium titanate, and lithium-aluminum alloys, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxides, 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.

[0122] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more combinations selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is less than 5% based on the total mass of the negative electrode film layer.

[0123] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is less than 5% based on the total mass of the negative electrode film layer.

[0124] In some embodiments, the negative electrode film may optionally include other additives. As examples, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of other additives is less than 2% based on the total mass of the negative electrode film.

[0125] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil or copper alloy foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more combinations selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymeric material substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0126] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0127] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet also includes a protective layer covering the surface of the negative electrode film layer.

[0128] [Electrolytes]

[0129] The secondary battery also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid-state.

[0130] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0131] 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.

[0132] 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.

[0133] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0134] [Isolation membrane]

[0135] In some embodiments, the secondary 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.

[0136] 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.

[0137] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0138] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0139] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0140] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0141] In some embodiments, such as Figure 1 and Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0142] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0143] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0144] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0145] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0146] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0147] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0148] Electrical appliances

[0149] Fourthly, this application provides an electrical device, which includes at least one of the secondary battery, battery module, and battery pack described in this application. The secondary battery, battery module, and battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0150] Electrical devices can be equipped with secondary batteries, battery modules, or battery packs depending on their usage requirements.

[0151] Figure 6 This is a schematic diagram of an example electrical device. The electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or a battery module can be used.

[0152] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0153] Example

[0154] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0155] Example 1

[0156] 1. Preparation of positive electrode sheet

[0157] 1.1 Preparation of Lithium Manganese Oxide Composite Material

[0158] A solvent and a coating material containing an organophosphonic acid or its salt are provided. The solvent and the coating material are mixed to form a coating slurry. The coating slurry is mixed with core particles LiMn2O4 and dried at 100°C in a pressure filtration process to form a coating layer on the surface of the core particles, thereby preparing a lithium manganese oxide composite material.

[0159] 1.2 Preparation of the positive electrode sheet

[0160] Aluminum foil with a thickness of 13μm was used as the positive electrode current collector.

[0161] The lithium manganese oxide composite material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet was obtained.

[0162] 2. Preparation of negative electrode sheet

[0163] A copper foil with a thickness of 8μm was used as the negative electrode current collector.

[0164] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0165] 3. Separating membrane

[0166] Porous polyethylene (PE) membrane is used as the separator.

[0167] 4. Preparation of electrolyte

[0168] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0169] 5. Preparation of secondary batteries

[0170] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0171] Example 2

[0172] Examples 2-1 to 2-3

[0173] The secondary battery was prepared in a similar manner to that in Example 1, except that the type of "coating material" was adjusted. Specific parameters are detailed in Tables 1 and 2.

[0174] Comparative Example

[0175] Comparative Example 1

[0176] The secondary battery was prepared in a similar manner to that in Example 1, except that the type of "coating material" was adjusted. Specific parameters are detailed in Tables 1 and 2.

[0177] Comparative Example 2

[0178] The secondary battery was prepared in a similar manner to that in Example 1, except that no coating material was used. Specific parameters are detailed in Tables 1 and 2. The preparation process of its positive electrode sheet is as follows:

[0179] Aluminum foil with a thickness of 13μm was used as the positive electrode current collector.

[0180] The core particles, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet is obtained.

[0181] Example 3

[0182] Examples 3-1 to 3-3

[0183] The secondary battery was prepared in a similar manner to that in Example 1, except that the type of "solvent" was adjusted to make the thickness of the coating layer uneven. Specific parameters are detailed in Tables 1 and 2.

[0184] Example 4

[0185] Examples 4-1 to 4-4

[0186] The secondary battery was prepared in a similar manner to that in Example 1, except that the content of the "coating material" was adjusted. Specific parameters are detailed in Tables 1 and 2.

[0187] Example 5

[0188] Examples 5-1 and 5-2

[0189] The secondary battery was prepared in a similar manner to that in Example 1, except that the type of "nuclear particles" was adjusted. Specific parameters are detailed in Tables 1 and 2.

[0190] Table 1

[0191]

[0192] In Table 1, the mass percentage of the core particles, a1%, refers to the mass percentage of the core particles relative to the total mass of the lithium manganese oxide composite material composed of the coating material and the core particles.

[0193] The mass percentage of the coating material (P%) refers to the mass percentage of the coating material relative to the total mass of the lithium manganese oxide composite material composed of the coating material and the core particles.

[0194] The solvent mass percentage a2% refers to the mass percentage of the solvent relative to the total mass of the solvent system.

[0195] Table 2

[0196]

[0197] Test section

[0198] 1. Performance testing of lithium manganese oxide composite materials

[0199] 1.1 Average thickness test of lithium manganese oxide composite material

[0200] A TEM image of the first region was obtained using a transmission electron microscope. Then, the average thickness at multiple (e.g., more than 30) different locations on the TEM image was measured, and the average value was taken as the average thickness H1 of the second region.

[0201] A TEM image of the second region was obtained using a transmission electron microscope. The average thickness of the second region was then measured at multiple (e.g., more than 30) different locations on the TEM image, and the average value was taken as the average thickness H2 of the first region.

[0202] 1.2 Test of the coating rate S% of the coating layer

[0203] The microstructure of the lithium manganese oxide composite material and the core particles was observed and qualitatively determined using a scanning electron microscope (SEM) of Carl Zeiss EVO MA 25, Germany.

[0204] 1.3 Elemental Analysis of Lithium Manganese Oxide Composite Materials

[0205] The carbon / metal / other non-metallic element content was determined using inductively coupled plasma emission spectra obtained with an Agilent ICP-OES730, and then the carbon / metal / other non-metallic element content was calculated from the ICP results.

[0206] A certain amount of the prepared negative electrode active material sample was added to a Bruker AXS D8-focus X-ray diffractometer (Germany) to obtain the X-ray diffraction pattern of the sample. The phase composition of the sample was then qualitatively determined by comparing the pattern with that of a standard substance. The testing standard referenced was JIS K0131-1996.

[0207] 1.4 pH test of lithium manganese oxide composite material

[0208] Tests were conducted using instruments and methods known in the art. For example, the material and solvent were added to an Erlenmeyer flask at a ratio of 1:9, stirred for 30 minutes using a magnetic stirrer, and allowed to stand for 1.5 hours after stirring. The pH value of the material was then measured using a magnetic pH meter at an environment of 15-28°C and humidity ≤80%. The average value of three tests was taken as the pH value of the material.

[0209] Specific surface area test of 1.5% lithium manganese oxide composite material

[0210] A certain amount of the prepared negative electrode active material sample was taken, and the specific surface area was measured using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method. The testing standard was based on GB / T 19587-2017.

[0211] 2. Performance testing of secondary batteries

[0212] 2.1 Storage performance test of secondary batteries at 45℃

[0213] 1. Under normal temperature conditions, charge the secondary battery at 0.33C to 4.3V, then charge it at 4.3V under constant voltage until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, then discharge it at 0.33C to 3V. Record the capacity M0 at this point. 2. Charge the full battery at 0.33C to 4.3V, then charge it at 4.3V under constant voltage until the current is less than or equal to 0.05mA. Finally, store it under constant temperature conditions of 45℃. 3. Repeat the above process every 15 days until the capacity decreases to 80% of M0. Record the number of storage days at this point.

[0214] 2.2 Cyclic performance test of secondary batteries at 45℃

[0215] Under a constant temperature environment of 45℃, the secondary battery is charged at 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After resting for 5 minutes, it is discharged at 1C to 3V, and the discharge capacity at this point is recorded as E0. The aforementioned charge-discharge cycle is repeated until the discharge capacity decreases to 80% of E0. The number of cycles completed by the secondary battery at this point is recorded.

[0216] Test Results

[0217] The role of this application in improving the cycle performance, storage performance and capacity of secondary batteries is shown in Table 3.

[0218] Table 3

[0219]

[0220] As shown in Table 3, Comparative Example 2 did not coat LiMn2O4, making it prone to manganese ion dissolution. This damages the positive electrode active material and may also damage the SEI film on the surface of the negative electrode active material, resulting in poor cycle and storage performance of the secondary battery. Comparative Example 1 used inorganic phosphate to coat LiMn2O4, which can alleviate manganese ion dissolution to some extent, but the effect is relatively small. The embodiments of this application use organophosphonic acid or its salts to coat LiMn2O4, which can significantly reduce manganese ion dissolution, thereby stabilizing manganese on the core particles and reducing the risk of manganese dissolving into the electrolyte, thus further improving the storage and cycle performance of the secondary battery. In particular, the improvement effect is better when the number of phosphonic acid groups n in the organophosphonic acid or its salts satisfies 2≤n≤4, especially when 2≤n≤3.

[0221] Examples 3-1 to 3-3 show that by adjusting the type of solvent, the thickness of the coating material formed on the surface of the core particles can be controlled, and the thickness is not uniform, which is beneficial to improving the kinetic performance of the secondary battery.

[0222] Examples 4-1 to 4-4 show that the coating effect on the nucleus particles can be adjusted by adjusting the mass percentage P of the coating layer.

[0223] Examples 5-1 to 5-2 show that the electrochemical performance of the positive electrode can be adjusted by changing the type of nuclear particles.

[0224] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium manganese oxide composite material, comprising: Nuclear particles, with the molecular formula Li 1+x Mn 2-y M y O 4-Z A z In the molecular formula, -0.2 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.1, 0 ≤ Z ≤ 0.1, M includes one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr, Mo, Nb, and Sn, and A includes one or more of F, Cl, and S; and A coating layer, which coats at least a portion of the outer surface of the core particle, the coating layer comprising an organophosphonic acid or a salt thereof. The covering layer includes a first region portion and a second region portion that are connected to each other; The average thickness of the first region is denoted as H1 nm, and the average thickness of the second region is denoted as H2 nm. The lithium manganese oxide composite material satisfies the following condition: 1 < H1 / H2 ≤ 3.

2. The lithium manganese oxide composite material according to claim 1, wherein, The organophosphonic acid or its salts include phosphonic acid groups, and the number of phosphonic acid groups is denoted as n, where 2 ≤ n ≤ 4.

3. The lithium manganese oxide composite material according to claim 2, wherein, 2≤n≤3。 4. The lithium manganese oxide composite material according to any one of claims 1 to 3, wherein, The organophosphonic acid or its salts include one or more of the following: aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, hydroxyethylidene diphosphonic acid, aminoethylidene diphosphonic acid, methylaminedimethylenephosphonic acid, hexamethylenediaminetetramethylenephosphonic acid, hydroxypropylidene diphosphonic acid, aminopropylphosphonic acid, potassium hexamethylenediaminetetramethylenephosphonate, sodium hydroxyethylidene diphosphonate, potassium hydroxyethylidene diphosphonate, nitrosotrimethylenephosphonic acid, and iminodimethylidene phosphonic acid.

5. The lithium manganese oxide composite material according to any one of claims 1 to 4, wherein, The coating layer covers the outer surface of the nuclear particle in a continuous layered form.

6. The lithium manganese oxide composite material according to any one of claims 1 to 5, wherein, The coating rate of the coating layer is denoted as S%, and the coating rate is the percentage of the total area of ​​the coating layer to the outer surface area of ​​the core particle; the lithium manganese oxide composite material satisfies: 50≤S≤95.

7. The lithium manganese oxide composite material according to claim 6, wherein, 50≤S≤80。 8. The lithium manganese oxide composite material according to any one of claims 1 to 7, wherein, Based on the total mass of the lithium manganese oxide composite material, the mass percentage of the coating layer is denoted as P%, and the lithium manganese oxide composite material satisfies: 0.01≤P≤5.

9. The lithium manganese oxide composite material according to claim 8, wherein, 0.1≤P≤2。 10. The lithium manganese oxide composite material according to any one of claims 1 to 9, wherein, The nucleus particles satisfy: -0.1≤x≤1.5, 0.001≤y≤0.06, 0.001≤Z≤0.05; and / or M includes one or more of Mg, Al and Sn, and A includes F and / or S.

11. The lithium manganese oxide composite material according to any one of claims 1 to 10, wherein, The pH value of the lithium manganese oxide composite material satisfies: 6≤pH≤8.

12. The lithium manganese oxide composite material according to claim 11, wherein, 6.5≤pH≤7.

5.

13. The lithium manganese oxide composite material according to any one of claims 1 to 12, wherein, The specific surface area of ​​the lithium manganese oxide composite material is denoted as BET g / cm³. 3 , BET≤1.

14. A method for preparing lithium manganese oxide composite materials, comprising: S100, providing a solvent and a coating material comprising an organophosphonic acid or a salt thereof, and mixing the solvent and the coating material into a coating slurry; S200, the coating slurry is supplied to the core particles to cure the coating slurry on at least a portion of the outer surface of the core particles to form a coating layer, thereby preparing a lithium manganese oxide composite material. The molecular formula of the nuclear particle is Li. 1+x Mn 2-y M y O 4-Z A z In the molecular formula, -0.2≤x≤0.2, 0≤y≤0.1, 0≤Z≤0.1, M includes one or more of Mg, Al, Ge, Fe, Zn, Co, Ni, Cr, and Sn, and A includes one or more of F, Cl, and S. The covering layer includes a first region portion and a second region portion that are connected to each other; The average thickness of the first region is denoted as H1 nm, and the average thickness of the second region is denoted as H2 nm. The lithium manganese oxide composite material satisfies the following condition: 1 < H1 / H2 ≤ 3.

15. The method according to claim 14, wherein, The solvent includes one or more of water, ethanol, and methanol.

16. The method according to claim 14 or 15, wherein, The mass ratio of the solvent to the coating material is denoted as Q, where 0 < Q ≤ 0.1; and / or the mass ratio of the solvent to the core particle is denoted as N, where 0 < N ≤ 0.

7.

17. The method according to any one of claims 14 to 16, wherein, The curing temperature is 80℃~120℃.

18. A secondary battery, comprising: The positive electrode comprises a lithium manganese oxide composite material as described in any one of claims 1 to 13 or a lithium manganese oxide composite material prepared by the method described in any one of claims 14 to 17.

19. An electrical device comprising the secondary battery as described in claim 18.

Images