A positive electrode active material, a battery cell, a battery device, and a power-using device

Abstract

This application relates to a positive electrode active material, a battery cell, a battery device, and an electrical device. The positive electrode active material includes a core and a first coating layer disposed on at least a portion of the surface of the core. The core includes lithium manganese iron phosphate, and the first coating layer includes lithium nickel manganese oxide. By coating with lithium nickel manganese oxide, the overall compaction density of the positive electrode active material is increased, which is beneficial to improving battery performance.

Description

Technical Field

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

[0002] Secondary batteries, represented by lithium-ion batteries, are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] The positive electrode active material has a significant impact on battery performance. Lithium phosphate is a promising positive electrode active material, but it has problems such as low compaction density to some extent. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode active material, a battery cell, a battery device, and an electrical device, wherein the positive electrode active material has good compaction density, which is beneficial to improving the energy density of the battery.

[0005] To this end, a first aspect of this application provides a positive electrode active material, which includes a core and a first coating layer disposed on at least a portion of the surface of the core;

[0006] The core includes lithium phosphate;

[0007] The first coating layer comprises lithium nickel manganese oxide.

[0008] Coating lithium nickel manganese oxide (LiMO) onto the surface of lithium phosphate can significantly improve the compaction density of the cathode active material. LiMO crystals consist of closely packed Ni / Mn-O octahedra with small atomic radii, forming a highly symmetrical cubic crystal structure with high atomic packing density and thus high compaction density. Therefore, coating lithium phosphate with LiMO is beneficial for improving the overall compaction density of the composite material.

[0009] In some embodiments, the lithium-containing phosphate includes lithium manganese iron phosphate.

[0010] Compared to lithium iron phosphate, lithium manganese iron phosphate (LFP) uses Mn to replace some Fe lattice sites, which can significantly increase the charge and discharge voltage of the material, thus improving its energy density. However, due to the difference in the radius of manganese and iron ions, LFP results in interstitial spaces between particles in the lattice, leading to a lower compaction density (typically 2.2~2.5 g / cm³). 3 By coating lithium nickel manganese oxide, which has a higher compaction density, the compaction density of composite cathode active materials can be significantly improved.

[0011] In some embodiments, the lithium manganese iron phosphate contains at least one of titanium and magnesium.

[0012] Titanium doping can occupy iron or manganese sites, forming stable tetravalent cation centers in the lithium manganese iron phosphate lattice and improving the structural integrity of the material during charge-discharge cycles. Magnesium doping can lengthen the Li-O covalent bonds in the LiO6 octahedron, which is beneficial for lithium-ion migration and improves the rate performance of the battery.

[0013] In some embodiments, the chemical formula of the lithium manganese iron phosphate is shown in Formula 1.

[0014] Li 1+a (Mn x1 Fe y1 M1 z1 M2 1-x1-y1-z1 )PO4 formula 1

[0015] Wherein, -0.2≤a≤0.2, 0<x1<1, 0<y1<1, 0≤z1≤0.05, 0≤1-x1-y1-z1≤0.05; M1 includes at least one of Ti and Mg, and M2 includes at least one of Al, Cu, Zn, Ni, V, Zr, Co, Ga, Sn, Sb, and Nb.

[0016] The above chemical formula can be used to represent lithium manganese iron phosphate in the positive electrode active material. It shows the stoichiometric range of each element and the possible doping elements. The fluctuating range of the lithium stoichiometric number (1+a) (-0.2≤a≤0.2) is due to the lithium intercalation / deintercalation behavior during battery charging and discharging. Lithium manganese iron phosphate using the above chemical formula has a rationally structured crystal lattice and exhibits good electrochemical performance.

[0017] In some embodiments, the particle size Dv50 of the positive electrode active material is 300 nm to 600 nm.

[0018] When using the aforementioned Dv50, it is more conducive to achieving close packing, thereby increasing compaction density. Furthermore, it is beneficial for slurry dispersion, has good compatibility with existing roll forming processes, and results in better coating uniformity.

[0019] In some embodiments, the lithium nickel manganese oxide contains at least one of the following elements: aluminum, phosphorus, and tungsten.

[0020] Aluminum doping improves the electronic conductivity of materials; the high Al-O bond energy alleviates structural collapse and reduces Mn dissolution, forming a stable SEI layer. Phosphorus doping enhances the surface structural stability of materials and also increases the electronic conductivity of the cathode active material surface. Tungsten doping enhances the structural stability of materials, forming a spinel phase on the surface, reducing surface oxygen content, strengthening the chemical bonds between transition metals and oxygen, suppressing the H2-H3 phase transition, and reducing microcrack formation.

[0021] In some implementations, the lithium nickel manganese oxide accounts for 0.8% to 2.5% of the total mass of the core and the first coating layer.

[0022] Overall, as the mass proportion of lithium nickel manganese oxide increases, the coating layer it forms on the surface of lithium manganese iron phosphate becomes more uniform and stable, which is beneficial for improving the compaction density of the composite material. However, the theoretical specific capacity of lithium nickel manganese oxide is lower than that of lithium manganese iron phosphate. Therefore, when the mass proportion of lithium nickel manganese oxide is high, it will reduce the overall capacity of the composite material to some extent. When lithium nickel manganese oxide has the aforementioned mass proportion, it can better balance improving compaction density and overall specific capacity of the material.

[0023] In some implementations, the lithium nickel manganese oxide accounts for 1% to 1.8% of the total mass of the core and the first coating layer.

[0024] When lithium nickel manganese oxide has the above-mentioned mass ratio, it is beneficial to better balance the improvement of compaction density and the overall specific capacity of the material.

[0025] In some embodiments, the positive electrode active material further includes a second coating layer comprising carbon; the second coating layer is disposed on the surface of the first coating layer and / or on the surface of the core not covered by the first coating layer.

[0026] Carbon coating can improve the overall electronic conductivity of composite materials, thereby improving the electrical connections between materials during battery charge-discharge cycles, reducing polarization, and enhancing the rate performance of the materials. Furthermore, carbon coating helps reduce direct contact between active materials and the electrolyte, minimizing side reactions; it also mitigates the dissolution of transition metal ions (such as manganese ions) during high-temperature cycling, reducing side reactions caused by transition metal dissolution.

[0027] In some embodiments, the mass percentage of carbon is 0.8% to 2% based on the total mass of the positive electrode active material.

[0028] When the mass percentage of carbon is greater than or equal to 0.8%, the second coating layer has a significant effect on improving the overall conductivity of the composite material and can significantly reduce the resistivity of the powder. When the mass percentage of carbon does not exceed 2%, lithium manganese iron phosphate can have a correspondingly higher mass percentage, which is beneficial for the composite material to have good specific capacity.

[0029] In some embodiments, the compacted density of the positive electrode active material at a pressure of 30,000 N is 2.35 g / cm³. 3 ~2.7g / cm 3 .

[0030] The positive electrode active material in the embodiments of the present invention has the above-mentioned high compaction density, so that when used as a positive electrode of a battery, a high positive electrode sheet compaction density can be achieved, which is beneficial to improving the energy density of the battery.

[0031] In some embodiments, the resistivity of the positive electrode active material is less than or equal to 80 Ω•cm.

[0032] The positive electrode active material in the embodiments of the present invention has the above-mentioned good powder resistivity. When it is applied to the positive electrode of the battery, it is beneficial to form a good conductive network, reduce polarization, and improve rate performance.

[0033] A second aspect of this application provides a battery cell, including a positive electrode, an electrolyte, and a negative electrode; the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector; the positive electrode material layer includes the positive electrode active material in any embodiment of the first aspect of this application.

[0034] In some embodiments, the compaction density of the positive electrode material layer is 2.3 g / cm³. 3 ~2.5g / cm 3 .

[0035] By adopting the aforementioned positive electrode active material, the positive electrode material layer can have the above-mentioned compaction density, which is beneficial for the battery to have excellent energy density.

[0036] A third aspect of this application provides a battery device including a battery cell as described in any embodiment of the second aspect of this application.

[0037] A fourth aspect of this application provides an electrical device, including a battery cell in any embodiment of the second aspect of this application, or a battery device in any embodiment of the third aspect of this application.

[0038] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, the specific implementation methods of this application are listed below. Attached Figure Description

[0039] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. In the drawings:

[0040] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0041] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0042] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0043] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0044] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0045] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application;

[0046] Figure 7 This is a transmission electron microscope (TEM) image of the positive electrode active material provided in one embodiment of this application;

[0047] Explanation of reference numerals in the attached figures:

[0048] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Casing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0049] Exemplary embodiments of this disclosure will now be described in more detail. It should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the 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 ​​1 and 2 are listed, and maximum range values ​​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 "a~b" 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.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0054] 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.

[0055] Secondary batteries, represented by lithium-ion batteries, have been widely used. Lithium-containing phosphates are promising positive electrode active materials, such as lithium iron phosphate and lithium manganese iron phosphate. However, they suffer from problems such as low compaction density to some extent.

[0056] This application mainly improves the compaction density of the material by setting a coating layer containing lithium nickel manganese oxide on the surface of lithium phosphate, thereby improving battery performance.

[0057] The solutions described in the embodiments of this application are applicable to positive electrode active materials, battery cells using the positive electrode active material, battery devices using the battery cells, and electrical devices using the battery cells or battery devices.

[0058] Positive electrode active material

[0059] In some embodiments of this application, a positive electrode active material is provided, which includes a core and a first coating layer disposed on at least a portion of the surface of the core;

[0060] The core includes lithium phosphate;

[0061] The first coating layer comprises lithium nickel manganese oxide.

[0062] Coating lithium nickel manganese oxide (LiMO) onto the surface of lithium phosphate can significantly improve the compaction density of the cathode active material. LiMO crystals consist of closely packed Ni / Mn-O octahedra with small atomic radii, forming a highly symmetrical cubic crystal structure with high atomic packing density and thus high compaction density. Therefore, coating lithium phosphate with LiMO is beneficial for improving the overall compaction density of the composite material.

[0063] The above-mentioned positive electrode active material can be detected using methods commonly used in this field. For example, 0.2 g of the positive electrode material is weighed into a 100 mL beaker, 10 mL of 10% w / w nitric acid solution is added, and the mixture is heated and digested at 120 °C for 0.5 hours. The solution is then diluted to volume with a 100 mL volumetric flask. Another 1 mL of the solution is pipetted into the 100 mL volumetric flask and diluted to volume to obtain the test solution. The mass fractions of lithium, manganese, iron, phosphorus, and doping elements in the test solution are determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, Agilent 5800). Based on the mass fractions of each element in the test solution of the powder, the molar percentage of each element in the positive electrode material is calculated, thereby determining the chemical formula and molar ratio of the positive electrode material.

[0064] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate and lithium manganese iron phosphate.

[0065] In some embodiments, the lithium-containing phosphate includes lithium manganese iron phosphate.

[0066] Compared to lithium iron phosphate, lithium manganese iron phosphate (LFP) uses Mn to replace some Fe lattice sites, which can significantly increase the charge and discharge voltage of the material, thus improving its energy density. However, due to the difference in the radius of manganese and iron ions, LFP results in interstitial spaces between particles in the lattice, leading to a lower compaction density (typically 2.2~2.5 g / cm³). 3 By coating lithium nickel manganese oxide, which has a higher compaction density, the compaction density of composite cathode active materials can be significantly improved.

[0067] In some embodiments, the lithium manganese iron phosphate contains at least one of titanium and magnesium.

[0068] Titanium doping can occupy iron or manganese sites, forming stable tetravalent cation centers in the lithium manganese iron phosphate lattice and improving the structural integrity of the material during charge-discharge cycles. Magnesium doping can lengthen the Li-O covalent bonds in the LiO6 octahedron, which is beneficial for lithium-ion migration and improves the rate performance of the battery.

[0069] In some embodiments, the chemical formula of the lithium manganese iron phosphate is shown in Formula 1.

[0070] Li 1+a (Mn x1 Fe y1 M1 z1 M2 1-x1-y1-z1 )PO4 formula 1

[0071] Wherein, -0.2≤a≤0.2, 0<x1<1, 0<y1<1, 0≤z1≤0.05, 0≤1-x1-y1-z1≤0.05; M1 includes at least one of Ti and Mg, and M2 includes at least one of Al, Cu, Zn, Ni, V, Zr, Co, Ga, Sn, Sb, and Nb.

[0072] The above chemical formula can be used to represent lithium manganese iron phosphate in the positive electrode active material. It shows the stoichiometric range of each element and the possible doping elements. The fluctuating range of the lithium stoichiometric number (1+a) (-0.2≤a≤0.2) is due to the lithium intercalation / deintercalation behavior during battery charging and discharging. Lithium manganese iron phosphate using the above chemical formula has a rationally structured crystal lattice and exhibits good electrochemical performance.

[0073] Dopant elements in lithium manganese iron phosphate (LFP) can be detected and their chemical formulas determined using methods commonly used in the field. For example, 0.2 g of the positive electrode active material is weighed into a 100 mL beaker, 10 mL of 10% w / w nitric acid solution is added, and the mixture is heated and digested at 120 °C for 0.5 hours. The solution is then diluted to volume with a 100 mL volumetric flask. Another 1 mL of the solution is pipetted into the 100 mL volumetric flask and diluted to volume to obtain the test solution. The mass fractions of lithium, manganese, iron, phosphorus, and dopant elements in the test solution are determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, Agilent 5800). Based on the mass fractions of each element in the test solution, the molar percentage of each element in the positive electrode active material is calculated, thereby determining the chemical formula and molar ratio of the positive electrode active material.

[0074] In some embodiments, the particle size Dv50 of the positive electrode active material is 300nm~600nm; for example, it can be about 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, etc.

[0075] When using the aforementioned Dv50, it is more conducive to achieving close packing, thereby increasing compaction density. Furthermore, it is beneficial for slurry dispersion, has good compatibility with existing roll forming processes, and results in better coating uniformity.

[0076] Particle size Dv50 is a well-known term in the art, referring to a particle size distribution where powder particles larger and smaller each account for 50%, and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0077] In some embodiments, the lithium nickel manganese oxide contains at least one of the following elements: aluminum, phosphorus, and tungsten.

[0078] Aluminum doping improves the electronic conductivity of materials; the high Al-O bond energy alleviates structural collapse and reduces Mn dissolution, forming a stable SEI layer. Phosphorus doping enhances the surface structural stability of materials and also increases the electronic conductivity of the cathode active material surface. Tungsten doping enhances the structural stability of materials, forming a spinel phase on the surface, reducing surface oxygen content, strengthening the chemical bonds between transition metals and oxygen, suppressing the H2-H3 phase transition, and reducing microcrack formation.

[0079] In some implementations, the mass percentage of lithium nickel manganese oxide is 0.8% to 2.5% based on the total mass of the core and the first coating layer; for example, it can be about 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, etc.

[0080] Overall, as the mass proportion of lithium nickel manganese oxide increases, the coating layer it forms on the surface of lithium manganese iron phosphate becomes more uniform and stable, which is beneficial for improving the compaction density of the composite material. However, the theoretical specific capacity of lithium nickel manganese oxide is lower than that of lithium manganese iron phosphate. Therefore, when the mass proportion of lithium nickel manganese oxide is high, it will reduce the overall capacity of the composite material to some extent. When lithium nickel manganese oxide has the aforementioned mass proportion, it can better balance improving compaction density and overall specific capacity of the material.

[0081] In some implementations, the lithium nickel manganese oxide accounts for 1% to 1.8% of the total mass of the core and the first coating layer.

[0082] When lithium nickel manganese oxide has the above-mentioned mass ratio, it is beneficial to better balance the improvement of compaction density and the overall specific capacity of the material.

[0083] In some embodiments, the positive electrode active material further includes a second coating layer comprising carbon; the second coating layer is disposed on the surface of the first coating layer and / or on the surface of the core not covered by the first coating layer.

[0084] Carbon coating can improve the overall electronic conductivity of composite materials, thereby improving the electrical connections between materials during battery charge-discharge cycles, reducing polarization, and enhancing the rate performance of the materials. Furthermore, carbon coating helps reduce direct contact between active materials and the electrolyte, minimizing side reactions; it also mitigates the dissolution of transition metal ions (such as manganese ions) during high-temperature cycling, reducing side reactions caused by transition metal dissolution.

[0085] In some embodiments, the mass percentage of carbon element is 0.8% to 2% based on the total mass of the positive electrode active material; for example, it can be about 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0086] When the mass percentage of carbon is greater than or equal to 0.8%, the second coating layer has a significant effect on improving the overall conductivity of the composite material and can significantly reduce the resistivity of the powder. When the mass percentage of carbon does not exceed 2%, lithium manganese iron phosphate can have a correspondingly higher mass percentage, which is beneficial for the composite material to have good specific capacity.

[0087] The carbon content in positive electrode active materials can be detected using methods commonly used in the art. For example, a certain amount (e.g., 1g) of positive electrode active material sample is weighed and placed in the crucible holder of an infrared carbon-sulfur analyzer. Under oxygen-enriched conditions, carbon and sulfur are oxidized into carbon dioxide and sulfur dioxide by high-temperature combustion in a high-frequency furnace. This gas is then processed and enters the corresponding absorption cell, where it absorbs the corresponding infrared radiation, which is then converted into a corresponding signal by a detector. This signal is sampled by a computer, linearly corrected, and converted into a value proportional to the concentrations of carbon dioxide and sulfur dioxide. The values ​​taken throughout the analysis process are then accumulated. After the analysis, this accumulated value is divided by the weight value in the computer, multiplied by the correction factor, and the blank is subtracted to obtain the carbon percentage in the sample.

[0088] In some embodiments, the compacted density of the positive electrode active material at a pressure of 30,000 N is 2.35 g / cm³. 3 ~2.7g / cm 3 For example, it could be approximately 2.35 g / cm³. 3 2.4g / cm 3 2.45g / cm 3 2.5g / cm 3 2.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.7g / cm 3 wait.

[0089] The positive electrode active material in the embodiments of the present invention has the above-mentioned high compaction density, so that when used as a positive electrode of a battery, a high positive electrode sheet compaction density can be achieved, which is beneficial to improving the energy density of the battery.

[0090] The compaction density of positive electrode active material powder can be determined using methods commonly used in the art. For example, a certain amount (e.g., 0.6g) of positive electrode active material sample is weighed and placed on a compaction-specific mold. The mold has a hollow center with two metal discs at the top and bottom. The powder is placed between the metal discs, and a metal cylinder is placed on top. The mold is then placed on an electronic pressure testing machine, and a pressure of 30,000N is set. The equipment can read the thickness of the powder under this pressure, and the compaction density can be obtained using p=m / V=m / (S×H).

[0091] In some embodiments, the resistivity of the positive electrode active material is less than or equal to 80 Ω•cm; for example, the resistivity of the powder can be about 80 Ω•cm, 70 Ω•cm, 60 Ω•cm, 50 Ω•cm, 40 Ω•cm, 30 Ω•cm, 20 Ω•cm, 10 Ω•cm, etc.

[0092] The positive electrode active material in the embodiments of the present invention has the above-mentioned good powder resistivity. When it is applied to the positive electrode of the battery, it is beneficial to form a good conductive network, reduce polarization, and improve rate performance.

[0093] The powder resistivity of the positive electrode active material can be detected using methods commonly used in the art. For example, a certain amount (e.g., 1g) of sample is weighed and placed in a mold, and then the mold is placed in a four-probe resistivity tester. The pressure is adjusted to 8.0MPa. After the mold height and pressure are stable, the forward resistivity and reverse resistivity of the sample are tested respectively, and the average of the two is taken as the powder resistivity of the sample.

[0094] Preparation of positive electrode active materials

[0095] In some embodiments, according to the mass ratio of lithium manganese iron phosphate core to lithium nickel manganese oxide coating layer, lithium manganese iron phosphate is first added to a high-speed mixer, while lithium nickel manganese oxide is added to the high-speed mixer according to the molar ratio of its elements, along with lithium, manganese, and nickel sources. After uniform mixing, the resulting powder is sintered at high temperature to prepare the positive electrode active material, whose core is lithium manganese iron phosphate and has a first coating layer formed by lithium nickel manganese oxide. When lithium nickel manganese oxide contains dopant elements, the precursor of the dopant element is added according to the corresponding molar ratio.

[0096] In some embodiments, according to the mass ratio of lithium manganese iron phosphate core to lithium nickel manganese oxide coating layer, lithium manganese iron phosphate after air jet milling is first added to a high-speed mixer, while lithium nickel manganese oxide is added to the high-speed mixer according to the molar ratio of its elements, along with lithium, manganese, and nickel sources. After uniform mixing, the resulting powder is placed in a crucible and then placed in a box furnace. The furnace is heated to 900-950°C at a heating rate of 2-3°C / min and held at that temperature for 8-10 hours. Lithium nickel manganese oxide heterogeneously nucleates on the surface of lithium manganese iron phosphate. After cooling, the material is removed to obtain the positive electrode active material, whose core is lithium manganese iron phosphate and has a first coating layer formed by lithium nickel manganese oxide. The lithium source can be one or more of lithium carbonate, lithium oxalate, and lithium hydroxide; the nickel source can be one or more of NiO, Ni2O3, and Ni3O4; and the manganese source can be one or more of MnO, Mn2O3, MnO2, and Mn3O4.

[0097] In some embodiments, lithium manganese iron phosphate can be co-doped with elements such as titanium and magnesium through a high-temperature solid-state sintering process. Taking the simultaneous doping of titanium and magnesium as an example, lithium source, manganese source, iron source, titanium source, and magnesium source are weighed according to the molar ratio of each element in the target material and added to a reactor containing deionized water for thorough stirring. The stirring rate is controlled at 200-300 rpm, and stirring is carried out for 2-3 hours to obtain a slurry. The slurry is then fed into a sand mill for grinding using 0.6-0.8 mm zirconium beads for 3-4 hours. The ground slurry is then spray-dried using a spray dryer with an inlet temperature of 180-200°C and an outlet temperature of 110-120°C to obtain powder. The powder is placed in a crucible and then placed in a box furnace, heated to 650-700°C at a heating rate of 3-5°C / min, held at that temperature for 8-10 hours, and then cooled to obtain titanium and magnesium co-doped lithium manganese iron phosphate material. The lithium source can be one or more of lithium carbonate, lithium oxalate, and lithium hydroxide; the phosphorus source can be one or more of phosphoric acid, iron phosphate, ferrous phosphate, ferrous ammonium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium monohydrogen phosphate, and lithium dihydrogen phosphate; the iron source can be one or more of iron hydroxide, iron(II,III) oxide, ferric oxide, ferrous phosphate, iron phosphate, ferrous oxalate, iron acetate, and iron sulfate; the manganese source can be one or more of manganese nitrate, manganese acetate, manganese phosphate, manganese oxalate, manganese carbonate, and manganese ammonium phosphate; the magnesium dopant source is one or more of magnesium oxide, magnesium acetate, and magnesium carbonate; and the titanium source is one or more of titanium dioxide, titanium sulfate, lithium titanate, and iron titanate.

[0098] In some embodiments, a positive electrode active material with lithium manganese iron phosphate as the core and having a first coating layer and a second coating layer can be prepared according to the following method. First, a positive electrode active material with lithium manganese iron phosphate as the core and having a first coating layer formed of lithium nickel manganese oxide is prepared according to the aforementioned method, and carbon coating is performed by chemical vapor deposition (CVD). For example, the aforementioned positive electrode active material with a core of lithium manganese iron phosphate and a first coating layer formed by lithium nickel manganese oxide can be placed in a carbon-coated rotary kiln. Inert gas is introduced for purging. After two hours of purging, the rotary kiln is heated at a certain rate while inert gas continues to be introduced, maintaining a slightly positive pressure inside the kiln. Once the rotary kiln reaches the specified temperature, the inert gas is stopped, and a gaseous carbon source is introduced, maintaining a slightly positive pressure inside the kiln. The material undergoes high-temperature CVD carbon coating for a certain period under a continuously flowing atmosphere. After the high-temperature CVD carbon coating is completed, the heating power is turned off, and the gaseous carbon source is stopped, thus obtaining a positive electrode active material with a core of lithium manganese iron phosphate and a first and second coating layer. The gaseous carbon source can be one or more combinations of methane, ethylene, acetylene, propane, methanol, ethanol, propylene, butane, and butene.

[0099] battery cell

[0100] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0101] In this embodiment of the application, the battery cell can be a lithium-ion battery.

[0102] [Electrode Assembly]

[0103] A single battery cell typically includes an electrode assembly. This assembly comprises a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0104] [Positive electrode plate]

[0105] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector;

[0106] The positive electrode material layer includes the positive electrode active material described in any embodiment of this application.

[0107] As mentioned above, the positive electrode active material provided in this application has excellent compaction density. When this positive electrode active material is used in a battery cell, a high positive electrode material layer compaction density can be achieved, thereby resulting in good energy density. Furthermore, when this positive electrode active material has other advantages, the battery cell also exhibits corresponding excellent performance.

[0108] In some embodiments, the compaction density of the positive electrode material layer is 2.3~2.5 g / cm³. 3 For example, it could be approximately 2.3 g / cm³. 3 2.35g / cm 3 2.4g / cm 3 2.45g / cm 3 2.5g / cm 3 wait.

[0109] By adopting the aforementioned positive electrode active material, the positive electrode material layer can have the above-mentioned compaction density, which is beneficial for the battery to have excellent energy density.

[0110] 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.).

[0111] The positive electrode active material may also include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphate include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0112] In some embodiments, the positive electrode material layer may optionally include a binder. For example, the binder may include one or more combinations of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0113] In some embodiments, the positive electrode material layer may optionally include a conductive agent. For example, the conductive agent may include one or more combinations of the following: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the positive electrode sheet can be prepared by dispersing the components of the above-mentioned positive electrode material layer, such as the positive electrode active material, the chelating agent, optional conductive agent, optional 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 then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0115] [Negative electrode plate]

[0116] The negative electrode sheet includes a negative electrode active material. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including the negative electrode active material.

[0117] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or 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.).

[0118] In some embodiments, the negative electrode active material layer may employ negative electrode active materials known in the art for lithium-ion batteries. For example, the negative electrode active material includes one or more combinations selected from the group consisting of: natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 Li-Al alloy.

[0119] In some embodiments, the negative electrode material layer may also optionally include a binder. For example, the binder may include one or more combinations selected from the group consisting 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).

[0120] In some embodiments, the negative electrode material layer may optionally include a conductive agent. For example, the conductive agent may include one or more combinations selected from the group consisting of: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the negative electrode material layer may also optionally include other additives. For example, other additives may be thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0122] In some embodiments, the negative electrode sheet can be prepared by dispersing the components of the above-mentioned negative electrode material layer, such as 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.

[0123] [Electrolytes]

[0124] In some embodiments, the battery cell further includes an electrolyte; the electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. The electrolyte can be liquid, gel-like, or solid.

[0125] Liquid electrolytes include electrolyte salts and solvents.

[0126] 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.

[0127] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0128] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0129] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0130] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0131] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0132] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductors, garnet, amorphous LiPON thin films), sulfide solid electrolytes (crystalline lithium superconducting ion conductors (lithium-germanium-phosphorus-sulfur, sulfosilium-germanium), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0133] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0134] [Isolation Component]

[0135] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0136] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0137] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0138] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0139] [Structure of the electrode assembly]

[0140] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0141] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0142] In some implementations, the electrode assembly is a stacked structure.

[0143] As an example, multiple positive and negative electrode plates can be set, and multiple positive and multiple negative electrode plates can be stacked alternately.

[0144] As an example, multiple positive electrode sheets can be set, and negative electrode sheets are folded to form multiple stacked folded segments, with a positive electrode sheet sandwiched between adjacent folded segments.

[0145] As an example, both the positive and negative electrode sheets are folded to form multiple stacked folded segments.

[0146] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0147] As an example, the separator can be continuously arranged between any adjacent positive or negative electrode plates by folding or rolling.

[0148] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0149] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0150] [shell]

[0151] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0152] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not impose any particular limitations. For example, Figure 1 This is an example of a square-shell battery cell 5.

[0153] In some implementations, refer to Figure 2 The outer casing includes an end cap 53 and a housing 51. The housing 51 has an opening, and the end cap 53 covers the opening. The housing 51 may have one or more openings. The end cap 53 may also have one or more. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within a receiving cavity formed by the housing 51 and the end cap 53. The electrolyte is immersed in the electrode assembly 52.

[0154] [Electrode terminals]

[0155] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0156] [Pressure relief mechanism]

[0157] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0158] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0159] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0160] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0161] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0162] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0163] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0164] Battery device

[0165] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0166] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0167] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties. Figure 3 This is battery module 4 as an example. (See reference...) Figure 3 In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way.

[0168] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0169] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing. Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery pack.

[0170] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0171] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0172] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0173] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0174] Electrical appliances

[0175] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft. Figure 6 This is an example of an electrical device. The electrical device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0176] Example 1

[0177] This embodiment provides a positive electrode active material and a lithium-ion battery.

[0178] I. Preparation of Positive Electrode Active Materials

[0179] This positive electrode active material uses titanium and magnesium co-doped lithium manganese iron phosphate as its core, sequentially coated with lithium nickel manganese oxide and a carbon coating layer. The specific preparation method is as follows:

[0180] (1) According to the chemical formula of titanium and magnesium co-doped lithium manganese iron phosphate (LiMn 0.6 Fe 0.36 Ti 0.02 Mg 0.02 The molar ratio of elements in FePO4 was determined by weighing FePO4, MnC2O4, Li2CO3, NH4H2PO4, TiO2, and MgO and adding them to a reactor containing deionized water. The mixture was stirred thoroughly at a stirring rate of 300 rpm for 2 hours to obtain a slurry. The slurry was then fed into a sand mill for grinding using 0.6-0.8 mm zirconium beads for 3 hours. The ground slurry was then spray-dried using a spray dryer with an inlet temperature of 200°C and an outlet temperature of 110°C to obtain powder. This powder was placed in a crucible and then placed in a box furnace. The furnace was heated to 650°C at a heating rate of 5°C / min and held at that temperature for 8 hours. After cooling, the powder was removed to obtain titanium and magnesium co-doped lithium manganese iron phosphate material.

[0181] (2) The titanium and magnesium co-doped lithium manganese iron phosphate material obtained in step (1) was processed using an air jet mill. The lithium manganese iron phosphate core and lithium nickel manganese oxide coating were added to a high-speed mixer according to a mass ratio of 98.6:1.4. The lithium nickel manganese oxide was added according to its elemental molar ratio (LiNi... 0.5 Mn 1.5O4) Add lithium, manganese and nickel sources to a high-speed mixer and mix at 1000 r / min, 1500 r / min and 2000 r / min for 10 minutes each. After mixing evenly, put the powder into a sagger and place it in a box furnace. Heat to 900°C at a heating rate of 2°C / min and hold for 10 hours. This allows lithium nickel manganese oxide to be coated on the surface of lithium manganese iron phosphate through heterogeneous nucleation. After cooling, remove the material to obtain lithium nickel manganese oxide coated with titanium and magnesium co-doped lithium manganese iron phosphate material.

[0182] (3) The nickel-manganese lithium oxide-coated titanium and magnesium co-doped lithium manganese iron phosphate material obtained in step (2) was placed in a rotary kiln and purged with nitrogen gas. After purging for two hours, the rotary kiln was heated at a rate of 5°C / min and nitrogen gas was continuously introduced. The pressure inside the kiln was kept slightly positive throughout the process. When the rotary kiln reached 1000°C, the nitrogen gas was stopped and a mixed gas was introduced. The mixed gas consisted of 20% methane and 80% argon. The pressure inside the kiln was kept slightly positive. The material was carbon-coated under a continuously flowing methane atmosphere for 5 hours. After the coating was completed, the heating power was turned off and the mixed gas was stopped. The temperature inside the kiln was allowed to drop to room temperature to obtain a positive electrode active material with titanium and magnesium co-doped lithium manganese iron phosphate as the core and nickel-manganese lithium oxide and carbon coating layers in sequence. The TEM image of the positive electrode active material is shown in [image missing]. Figure 7 As shown, the particle size Dv50 is 450 nm, the mass percentage of carbon is 1.2%, and the compacted density of the powder under a pressure of 30000 N is 2.552 g / cm³. 3 The powder resistivity is 30 Ω•cm.

[0183] II. Fabrication of Button Lithium-ion Batteries

[0184]

Positive Electrode

[0185] The above-mentioned positive electrode active material, super carbon black as a conductive agent, and sodium carboxymethyl cellulose as a binder were mixed evenly in a mass ratio of 80:10:10 to obtain a slurry for forming the positive electrode material layer. This slurry was then coated onto an aluminum current collector to prepare a negative electrode film, which was vacuum dried at 80°C for 12 hours. The dried film was cut into circular pieces with a diameter of 14 mm to serve as the positive electrode sheets. The compaction density of the positive electrode material layer was 2.4 g / cm³. 3 .

[0186] Counter electrode plate

[0187] Lithium metal is used as the counter electrode.

[0188] Electrolyte

[0189] The electrolyte is formed by dissolving LiPF6 in a mixed solvent of ethylene carbonate / dimethyl carbonate (EC / DMC) in a volume ratio of 1:1.

[0190]

Isolation Film

[0191] Celgard 2400 separator membrane.

[0192] Fabrication of button-type lithium-ion batteries

[0193] The prepared positive electrode, the lithium metal sheet used as the counter electrode, and the electrolyte are assembled into a coin cell lithium-ion battery.

[0194] Perform the following tests and record the results in Table 1:

[0195] 1. Test of charge / discharge specific capacity

[0196] Electrochemical performance testing was conducted using a Wuhan Land2001A electrochemical performance tester. The assembled battery was left to stand for 12 hours to allow the electrolyte to fully wet the negative electrode. The battery was then clamped onto the alligator clips of the tester. The test current, the mass of the active material, and the test voltage range were input. The tester itself displayed the battery's charge and discharge specific capacities. The test voltage range was 0.01-2V, the current density was 100mA / g, the test current = current density × mass of active material, the mass of active material = slurry mass × 80%, and the slurry mass = wafer mass - blank current collector mass.

[0197] 2. Test of capacity retention at 25℃

[0198] The Shenzhen Xinwei Battery Testing System was used to perform 1000 charge-discharge cycles on the coin cells at a 1C charge-discharge rate. The test temperature was 25.0 ℃, and the charge-discharge voltage was 2.0V~4.3V. The capacity retention rate was obtained by dividing the discharge capacity of the last cycle by the discharge capacity of the first cycle.

[0199] Comparative Example 1

[0200] Except for the absence of the lithium nickel manganese oxide coating layer, i.e. the absence of step (2), the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 1.

[0201] Examples 2-5

[0202] Except for changing the mass ratio of lithium manganese iron phosphate core to lithium nickel manganese oxide coating layer as shown in Table 1, the preparation and testing were carried out according to the same steps as in Example 1, and the results are shown in Table 1.

[0203] In Table 1, the "mass ratio of lithium nickel manganese oxide coating" is calculated based on the sum of the masses of the lithium manganese iron phosphate core and the lithium nickel manganese oxide coating.

[0204] Table 1

[0205]

[0206] Comparing Examples 1-5 with Comparative Example 1, it is evident that the application of a lithium nickel manganese oxide coating layer improves the compaction density of the cathode active material powder. The comparison of Examples 1-5 shows that, on the one hand, the higher the mass percentage of the lithium nickel manganese oxide coating layer, the more significant the improvement in compaction density. On the other hand, the mass percentage of the lithium nickel manganese oxide coating layer also affects the charge / discharge specific capacity. When its mass percentage is low (e.g., Example 2), the small amount of lithium nickel manganese oxide may make it difficult to form a uniform and stable coating on the surface of lithium manganese iron phosphate, resulting in an unsatisfactory capacity release effect of the composite cathode active material. When its mass percentage is high (e.g., Example 5), the mass percentage of lithium manganese iron phosphate decreases accordingly, and the theoretical specific capacity of lithium nickel manganese oxide is lower than that of lithium manganese iron phosphate, leading to a decrease in the overall capacity of the material. Therefore, when the mass percentage of the lithium nickel manganese oxide coating layer is between 1% and 1.8%, it has a more balanced improvement effect on both powder compaction density and charge / discharge specific capacity.

[0207] Examples 6-10

[0208] Except for changing the amount of precursor to make the stoichiometric coefficients of the doping elements in lithium manganese iron phosphate as shown in Table 2, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 2.

[0209] Table 2

[0210]

[0211] Based on the above results and the principle analysis, it can be seen that the amount of titanium doping mainly affects the structural stability of the material, thus primarily impacting the improvement in capacity retention. The amount of magnesium doping mainly affects the rate performance of the battery, possibly because the incorporation of magnesium alters the lithium-ion transport path. By doping with magnesium and titanium, the rate performance and cycle capacity retention of the battery have been improved; further optimization of the doping amounts of both can yield significantly better results.

[0212] Examples 11-12

[0213] Except for adjusting the time of introducing the mixed gas in the carbon coating step to make the carbon content as shown in Table 3, the preparation and testing were carried out in the same manner as in Example 1, and the results are shown in Table 3.

[0214] Table 3 shows the carbon content calculated based on the total mass of the positive electrode active material.

[0215] Table 3

[0216]

[0217] Examples 13-14

[0218] Except for adjusting the particle size of the core so that the particle size Dv50 of the positive electrode active material is as shown in Table 4, and making the powder compaction density of the positive electrode active material and the compaction density of the positive electrode material layer as shown in Table 4, the preparation and testing were carried out in the same way as in Example 1, and the results are shown in Table 4.

[0219] Table 4

[0220]

[0221] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes a core and a first coating layer disposed on at least a portion of the surface of the core; The core includes lithium phosphate; The first coating layer includes lithium nickel manganese oxide; The lithium-containing phosphate includes lithium manganese iron phosphate, the chemical formula of which is shown in Formula 1. Li 1+a (Mn x1 Fe y1 M1 z1 M2 1-x1-y1-z1 )PO₄ Formula 1 Wherein, -0.2≤a≤0.2, 0<x1<1, 0<y1<1, 0≤z1≤0.05, 0≤1-x1-y1-z1≤0.05; M1 includes at least one of Ti and Mg, and M2 includes at least one of Al, Cu, Zn, Ni, V, Zr, Co, Ga, Sn, Sb, and Nb.

2. The positive electrode active material as described in claim 1, characterized in that, The lithium manganese iron phosphate contains at least one of titanium and magnesium.

3. The positive electrode active material as described in claim 1, characterized in that, The particle size Dv50 of the positive electrode active material is 300nm~600nm.

4. The positive electrode active material as described in claim 1, characterized in that, The lithium nickel manganese oxide contains at least one of the following elements: aluminum, phosphorus, and tungsten.

5. The positive electrode active material as described in claim 1, characterized in that, Based on the total mass of the core and the first coating layer, the mass percentage of the lithium nickel manganese oxide is 0.8% to 2.5%.

6. The positive electrode active material as described in claim 5, characterized in that, Based on the total mass of the core and the first coating layer, the mass percentage of the lithium nickel manganese oxide is 1% to 1.8%.

7. The positive electrode active material as described in claim 1, characterized in that, The positive electrode active material further includes a second coating layer, the second coating layer comprising carbon; the second coating layer is disposed on the surface of the first coating layer, and / or on the surface of the core not covered by the first coating layer.

8. The positive electrode active material as described in claim 7, characterized in that, Based on the total mass of the positive electrode active material, the mass percentage of carbon is 0.8% to 2%.

9. The positive electrode active material according to any one of claims 1 to 8, characterized in that, The compacted density of the positive electrode active material under a pressure of 30,000 N is 2.35 g / cm³. 3 ~2.7g / cm 3 .

10. The positive electrode active material according to any one of claims 1 to 8, characterized in that, The resistivity of the positive electrode active material powder is less than or equal to 80 Ω•cm.

11. A single battery cell, characterized in that, It includes a positive electrode, an electrolyte, and a negative electrode; the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector; the positive electrode material layer includes the positive electrode active material according to any one of claims 1 to 10.

12. The battery cell as described in claim 11, characterized in that, The compaction density of the positive electrode material layer is 2.3 g / cm³. 3 ~2.5g / cm 3 .

13. A battery device, characterized in that, Includes the battery cell described in claim 11 or 12.

14. An electrical appliance, characterized in that, Includes the battery cell as described in claim 11 or 12, or the battery device as described in claim 13.

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