Positive electrode active material, positive electrode slurry, positive electrode sheet, battery, and vehicle

Abstract

The present application belongs to the technical field of batteries, and provides a positive electrode active material, a positive electrode slurry, a positive electrode plate, a battery, and a vehicle. The positive electrode active material comprises lithium manganese iron phosphate and lithium nickel cobalt manganate. The mass ratio of the lithium manganese iron phosphate to the lithium nickel cobalt manganate is (50-95):(5-50). The general chemical formula of the lithium nickel cobalt manganate is LiNiaCobMn( 1-a-b) )O2, 0.6≤a<1, 0<b<0.5, and 0<a+b<1.

Description

A positive electrode active material, a positive electrode slurry, a positive electrode sheet, a battery, and a vehicle.

[0001] This application claims priority to Chinese Patent Application No. 202411458540.4, filed on October 17, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a positive electrode active material, a positive electrode slurry, a positive electrode sheet, a battery, and a vehicle. Background Technology

[0003] With the continuous advancement of battery technology, the energy density of lithium iron phosphate (LFP) has reached a bottleneck, leading researchers to increasingly focus on lithium manganese iron phosphate (LMFP). LMFP shares the same olivine structure as LFP, exhibiting good structural stability while retaining the safety and cycle life advantages of LFP. Furthermore, the introduction of manganese into LMFP allows for an average discharge voltage of 3.6V, resulting in a relatively higher energy density compared to LFP. However, compared to ternary lithium-ion batteries, LMFP still exhibits significant limitations in energy density. Invention Overview

[0004] In related technologies, lithium manganese iron phosphate and ternary materials are often mixed to improve the overall performance of the battery. However, the mixing system in these technologies mainly aims to increase the battery's energy density to reduce costs, neglecting the battery's safety performance. This results in a battery that cannot simultaneously achieve both energy density and safety performance, creating potential safety hazards.

[0005] This application provides a positive electrode active material, including lithium manganese iron phosphate and lithium iron phosphate rich in lithium. Specifically, it includes lithium manganese iron phosphate and lithium nickel cobalt manganese oxide. The mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is (50-95):(5-50). The general chemical formula of lithium nickel cobalt manganese oxide is: LiNi a Co b Mn （1-a-b） O2, 0.6≤a<1, 0<b<0.5, 0<a+b<1.

[0006] This application also provides a positive electrode slurry, including the positive electrode active material described above.

[0007] This application also provides a positive electrode sheet, comprising a positive electrode foil and a positive electrode active layer coated on the positive electrode foil. The positive electrode active layer is prepared using the positive electrode slurry described above, or the positive electrode active layer comprises the positive electrode active material described above.

[0008] This application also provides a battery, including the positive electrode plate described above.

[0009] This application also provides a vehicle including the battery described above. Beneficial effects

[0010] The positive electrode active material provided in this application includes lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, and the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is (50-95):(5-50). The general chemical formula of lithium nickel cobalt manganese oxide is: LiNi a Co b Mn （1-a-b） O2, 0.6≤a<1, 0<b<0.5, 0<a+b<1. Lithium manganese iron phosphate has the same olivine-type crystal structure as lithium iron phosphate, exhibiting high safety performance, but its energy density is lower than that of ternary materials. The general chemical formula of lithium nickel cobalt manganese oxide in this application is: LiNi a Co b Mn （1-a-b） O2, 0.6≤a<1, 0<b<0.5, 0<a+b<1, meaning that in lithium nickel cobalt manganese oxide, the molar content of nickel accounts for more than 60% of the total molar content of nickel, cobalt, and manganese, resulting in high energy density. However, due to the high nickel content, it suffers from poor thermal stability, reducing its safety when used in batteries. This application uses a composite of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide as the positive electrode active material, controlling their mass ratio within the range of (50-95):(5-50). This ensures that when the positive electrode active material with a mass proportion of lithium nickel cobalt manganese oxide not exceeding 50% is used in batteries, it can achieve both high safety performance and high energy density, thus improving overall performance.

[0011] The positive electrode slurry provided in this application embodiment, by including the positive electrode active material described above, can have both high safety performance and high energy density, thereby improving overall performance.

[0012] The positive electrode provided in this application embodiment can have both high safety performance and high energy density, thus improving the overall performance.

[0013] The battery provided in this application embodiment can have both high safety performance and high energy density, thus improving overall performance. Attached Figure Description

[0014] Figure 1 is a thermal runaway test curve of the lithium-ion battery in Embodiment 2 of this application;

[0015] Figure 2 is a thermal runaway test curve of the lithium-ion battery in Comparative Example 1.

[0016] Figure 3 is a thermal runaway test curve of the lithium-ion battery in Comparative Example 2.

[0017] Figure 4 shows the room temperature rate discharge diagrams of some embodiments and comparative examples of this application. Embodiments of the present invention

[0018] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0019] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, where the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, where the first feature is at a lower horizontal level than the second feature.

[0020] In the description of this embodiment, the terms "upper," "lower," "left," "right," "front," and "rear," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for distinction in description and have no special meaning.

[0021] In one aspect, embodiments of this application provide a positive electrode active material, comprising lithium manganese iron phosphate (LMFP) and lithium nickel cobalt manganese oxide (NCM). The mass ratio of LMFP to NCM is (50-95):(5-50). The general chemical formula of lithium nickel cobalt manganese oxide is: LiNi a Co b Mn （1-a-b） O2, 0.6≤a<1, 0<b<0.5, 0<a+b<1. Lithium manganese iron phosphate has the same olivine-type crystal structure as lithium iron phosphate, offering high safety performance, but its energy density is lower than that of ternary materials. In the embodiments of this application, the general chemical formula of lithium nickel cobalt manganese oxide is: LiNi a Co b Mn （1-a-b）O2, 0.6≤a<1, 0<b<0.5, 0<a+b<1, meaning that in lithium nickel cobalt manganese oxide, the molar content of nickel accounts for more than 60% of the total molar content of nickel, cobalt, and manganese, resulting in high energy density. However, due to the high nickel content, it suffers from poor thermal stability, reducing its safety when used in batteries. This application's embodiments use a composite of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide as the positive electrode active material, controlling their mass ratio within the range of (50-95):(5-50). This allows the positive electrode active material to achieve both high safety and high energy density when applied to batteries, improving overall performance.

[0022] Specifically, lithium manganese iron phosphate (LMFP) has the same olivine-type crystal structure as lithium iron phosphate (LFP), both belonging to the orthorhombic crystal system and the Pnma space group. The general chemical formula of lithium manganese iron phosphate is LiMn. x Fe （1-x） PO4, 0 < x < 1. Each LMFP unit cell consists of four basic units, where lithium (Li) and manganese (iron) [Mn (Fe)] are located at the 4a and 4c sites of the octahedron, respectively, forming deformed LiO6 and MnO6 (FeO6) octahedra. Furthermore, phosphorus (P) and oxygen (O) form PO4 tetrahedra, located at the 4c ​​site of the tetrahedron. Due to the strong PO covalent bonds formed between P and O, O is difficult to remove from the crystal structure, thus LMFP exhibits relatively high safety performance. Ternary materials possess high theoretical specific capacity (>250 mAh / g) and high operating voltage (~3.65 V), making them the mainstream high-energy-density cathode materials. However, as the nickel content in ternary materials increases, their thermal stability decreases. When the molar content of nickel in lithium nickel cobalt manganese oxide is above 60%, its safety performance is poor when it is directly applied to batteries. This application improves the overall performance by compounding lithium manganese iron phosphate and high-nickel lithium nickel cobalt manganese oxide in a mass ratio of (50-95):(5-50).

[0023] For example, the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide can be 95:5, 90:10, 80:20, 70:30, 60:40, or 50:50. The chemical formula of lithium nickel cobalt manganese oxide can be: LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2 or LiNi 0.8 Co0.1 Mn 0.1 O2.

[0024] In some embodiments, the median particle size D50 of lithium manganese iron phosphate is 0.5 μm - 5 μm, and the specific surface area is 14 m². 2 / g-25m 2 / g. The particle size of lithium manganese iron phosphate (LFP) affects its electrochemical and mechanical properties. Smaller LFP particles have a larger specific surface area, providing more active sites and accelerating lithium-ion insertion and extraction reactions. Smaller LFP particles also have shorter ion diffusion paths, allowing lithium ions to migrate more rapidly during charge and discharge, reducing stress concentration and lattice distortion caused by prolonged charge and discharge, thus improving the material's structural stability. However, if the LFP particle size is too small, it is prone to agglomeration, increasing the preparation difficulty and potentially reducing the mechanical strength of the LFP material, affecting its cycle life and stability. Therefore, in this embodiment, the median particle size D50 of LFP is set to 0.5 μm-5 μm. The specific surface area of ​​LFP is related to its particle size; larger particle sizes result in smaller specific surface areas, and smaller particle sizes result in larger specific surface areas. Accordingly, in this embodiment, the specific surface area of ​​LFP is set to 14 m². 2 / g-25m 2 / g.

[0025] For example, the median particle size D50 of lithium manganese iron phosphate can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm;

[0026] For example, the specific surface area of ​​lithium manganese iron phosphate is 14 m². 2 / g、16 m 2 / g、18 m 2 / g、20 m 2 / g、22 m 2 / g or 25m 2 / g.

[0027] In some embodiments, the median particle size D50 of lithium nickel cobalt manganese oxide is 4 μm-18 μm, and the specific surface area is 0.2 m². 2 / g -1.5 m 2 Similar to lithium manganese iron phosphate, the particle size of lithium nickel cobalt manganese oxide (LiMO) also affects its electrochemical performance and cycle life. When using LiMO in batteries, if the particle size is too small, side reactions increase, reducing battery safety. If the particle size is too large, the battery capacity may be too low. By controlling the particle size of LiMO within a certain range, it is possible to improve the charge / discharge efficiency and cycle life of the battery while ensuring safety.

[0028] For example, the median particle size D50 of lithium nickel cobalt manganese oxide can be 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm or 18 μm;

[0029] For example, the specific surface area of ​​lithium nickel cobalt manganese oxide is 0.2 m². 2 / g, 0.5m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.2m 2 / g or 1.5m 2 / g.

[0030] In some embodiments, the chemical formula of lithium manganese iron phosphate is LiMn 0.6 Fe 0.4 PO4. LiMn 0.6 Fe 0.4 The high manganese content in PO4 contributes to higher energy density. Manganese stabilizes the material's structure during charge and discharge, reducing lattice distortion and stress concentration, thus extending cycle life. Furthermore, the higher manganese content also helps improve the low-temperature performance and safety of lithium manganese iron phosphate.

[0031] In some embodiments, the chemical formula of lithium nickel cobalt manganese oxide is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2 and LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2. LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2 and LiNi 0.9 Co 0.05 Mn 0.05The high nickel content in O2 significantly improves the energy density of lithium nickel cobalt manganese oxide (LiCO). Nickel exhibits high reactivity during charge and discharge, contributing more to capacity. Furthermore, the higher nickel content helps optimize the cycle stability and charge / discharge efficiency of LiCO. During charge and discharge, the reactivity of nickel facilitates lithium-ion insertion and extraction, reducing structural changes and capacity decay. Nickel's good conductivity accelerates electron transport within the material, shortening charge / discharge time and improving efficiency. In addition, the increased nickel content corresponds to a decrease in cobalt content, thus reducing material cost. Cobalt is a rare and expensive metal, while nickel is relatively abundant and inexpensive.

[0032] In some embodiments, the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is 90:10. The higher proportion of lithium manganese iron phosphate ensures safety performance and significantly improves energy density compared to using lithium manganese iron phosphate alone in the positive electrode active material.

[0033] In other embodiments, the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is 70:30. By increasing the proportion of lithium nickel cobalt manganese oxide added, the energy density can be further improved while ensuring safety performance.

[0034] In other embodiments, the mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is 50:50. This ratio ensures that no fire or explosion occurs during thermal runaway, passes overcharge tests, and significantly improves energy density due to the further increase in the proportion of lithium nickel cobalt manganese oxide.

[0035] Secondly, embodiments of this application provide a positive electrode slurry, comprising the positive electrode active material as described above.

[0036] The positive electrode slurry provided in this application embodiment has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0037] In some embodiments, the positive electrode slurry further includes a positive electrode conductive agent, a positive electrode binder, and a positive electrode dispersant. The mass ratio of the positive electrode active material, positive electrode conductive agent, positive electrode binder, and positive electrode dispersant is (95-98):(0.5-2.5):(1-3):(0-1). The positive electrode active material is a key component for storage and release in the battery. A higher proportion of positive electrode active material helps improve the battery's energy density. Under the same volume or weight, the battery can store more electrical energy, thus extending its service life. An appropriate amount of positive electrode conductive agent helps form an effective conductive network, reduces the battery's internal resistance, and improves electron and ion transport rates, thereby enhancing the battery's charge and discharge performance. The positive electrode binder plays a crucial role in maintaining the structural integrity and stability of the positive electrode sheet. By controlling the addition ratio of the positive electrode binder within a suitable range, it is possible to ensure that the positive electrode active material does not detach under the expansion and contraction during charge and discharge, maintaining structural stability and thus improving the battery's cycle life and safety. The dispersant helps improve the flowability of the positive electrode slurry, ensuring that the positive electrode active material is evenly distributed.

[0038] In some embodiments, the positive electrode conductive agent includes at least one of carbon nanotubes, graphene, and acetylene black. Carbon nanotubes possess high electrical conductivity, and using them as a positive electrode conductive agent helps reduce battery internal resistance and improve battery charge-discharge efficiency. Furthermore, carbon nanotubes exhibit good mechanical strength and flexibility, capable of withstanding volume changes in the positive electrode active material during charge-discharge, reducing the risk of particle breakage and structural damage to the positive electrode active material, thereby improving battery cycle stability. When used as a positive electrode conductive agent, the amount of carbon nanotubes added can be reduced, helping to increase the proportion of positive electrode active material added, thus increasing the battery's energy density. Graphene has a large specific surface area, which helps to form electrolyte storage voids, increasing the contact area between the positive electrode active material and the electrolyte, thereby enhancing battery charge-discharge efficiency. Graphene also possesses excellent mechanical properties, which can improve the volumetric energy density of the positive electrode sheet, increase the bendability and peel strength of the positive electrode sheet, thereby improving the overall stability of the battery. In addition, graphene has good thermal conductivity, which can reduce the battery's thermal resistance and improve its thermal stability. Acetylene black has moderate thermal conductivity, low nitrogen cost, and good mechanical stability, which can inhibit material shedding and damage.

[0039] Thirdly, embodiments of this application provide a positive electrode sheet, including a positive electrode foil and a positive electrode active layer coated on the positive electrode foil. The positive electrode active layer is prepared using the positive electrode slurry described above, or the positive electrode active layer includes the positive electrode active material described above.

[0040] The positive electrode sheet provided in this application embodiment also has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0041] In some embodiments, the positive electrode foil is a carbon-coated aluminum foil. The carbon-coated aluminum foil includes an aluminum foil and a carbon coating layer coated on the aluminum foil, wherein the thickness of the aluminum foil is 6 μm-20 μm, and the thickness of the carbon coating layer is greater than 0 μm and less than or equal to 1 μm.

[0042] The carbon-coated aluminum foil comprises aluminum foil and a carbon coating layer applied to the aluminum foil. The carbon coating layer optimizes the surface properties of the aluminum foil, allowing the positive electrode slurry to adhere more tightly and uniformly to the foil, reducing ineffective space and thus improving the battery's energy density. Setting the aluminum foil thickness between 6μm and 20μm ensures sufficient mechanical strength while reducing battery weight and increasing energy density. The carbon coating layer thickness is set within the range of greater than 0μm and less than or equal to 1μm, resulting in an ultra-thin and uniform coating that contributes to improved overall battery performance.

[0043] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylic acid (PAA). PVDF possesses excellent chemical stability and corrosion resistance, ensuring reliability and safety during use. PVDF also exhibits good high-voltage resistance, remaining stable under high voltage conditions without oxidation or deterioration. It has good solubility and dissolution rate, enabling uniform dispersion onto the positive electrode slurry and positive electrode sheet surface, thus forming a uniform adhesive layer. Furthermore, its high flexibility and adhesion strength reduce the shedding of the positive electrode active material during repeated expansion and contraction. PTFE exhibits excellent corrosion resistance, strong stability, and good high-temperature stability, allowing for long-term use at high temperatures without decomposition. PAA possesses good adhesion, connecting with functional groups on the surface of the positive electrode active material through hydrogen bonds, thereby forming a stable adhesive layer and helping to prevent the shedding and pulverization of the positive electrode active material. PAA also effectively suppresses the volume expansion of the positive electrode active material during charge and discharge, thus extending the battery's cycle life. Furthermore, PAA itself has a small coefficient of volume expansion and a large coefficient of thermal diffusivity, making it safer to use as a positive electrode binder when the battery is used under high power charging and discharging and high temperature conditions.

[0044] Fourthly, embodiments of this application provide a battery including the positive electrode sheet as described above.

[0045] The battery provided in this application embodiment also has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0046] In some embodiments, the battery further includes a negative electrode, an electrolyte, and a separator.

[0047] The negative electrode sheet comprises negative electrode foil, negative electrode active material, negative electrode conductive agent, and negative electrode binder. The negative electrode foil is made of copper foil or copper mesh, with a thickness of 4μm-12μm. Copper foil and copper mesh possess excellent conductivity and low resistivity, enabling rapid conduction of current within the battery. Using them as negative electrode foil provides an efficient conductive channel for the insertion and extraction of lithium ions, thereby improving the battery's charge and discharge efficiency and response speed. The high mechanical strength of copper foil and copper mesh protects the internal battery structure, increasing its stability and strength. By controlling the thickness of the negative electrode foil to 4μm-12μm, both structural strength and the energy density of the battery can be increased by reducing the mass of the negative electrode foil.

[0048] The negative electrode conductive agent is at least one of carbon nanotubes, carbon black, and acetylene black. The advantages of carbon nanotubes and acetylene black have been described in the section on positive electrode conductive agents; their application in negative electrode conductive agents offers similar advantages and will not be repeated here. Carbon black possesses excellent conductivity, which can improve the conductivity of the negative electrode sheet, reduce battery internal resistance, and allow for uniform dispersion within the negative electrode active material, forming a conductive network, accelerating electron transport rates, and improving battery performance. By using carbon black as the negative electrode conductive agent, conductivity can be significantly improved with a relatively low addition amount, facilitating an increase in the amount of negative electrode active material added to the negative electrode sheet. Furthermore, carbon black exhibits excellent chemical and physical stability, low cost, and good compatibility with other materials.

[0049] The electrolyte comprises an electrolyte, an organic solvent, and additives. The electrolyte is at least one of lithium hexafluorophosphate (LIPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The organic solvent comprises at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), polycarbonate (PC), and ethyl methyl carbonate (EMC). The additives comprise at least one of vinylene carbonate (VC), ethylene sulfate (DTD), methanedisulfonate (MMDS), lithium bis(oxalato)borate (LiBOB), and 1,3-propanesulfonyl lactone (PS), with the additive content ranging from 0.2% to 1.5% of the total electrolyte mass.

[0050] The diaphragm comprises a base membrane and a diaphragm coating applied to the base membrane. The base membrane is made of polypropylene (PP) or polyethylene (PE). The diaphragm coating is made of at least one of alumina, boehmite, magnesium hydroxide, and barium sulfate. The base membrane has a thickness of 5 μm–16 μm, the diaphragm coating has a thickness of 0.5 μm–5 μm, and the tensile strength of the diaphragm is greater than 200 MPa.

[0051] Fifthly, embodiments of this application provide a vehicle including the battery as described above.

[0052] The vehicle provided in this application embodiment also has the beneficial effects of the above-mentioned positive electrode active material, which will not be repeated here.

[0053] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.

[0054] It should be noted that, except for the conditions stated in the embodiments and comparative examples, the conditions in the embodiments and comparative examples are the same.

[0055] Example 1

[0056] In this embodiment: the positive electrode active material in the positive electrode sheet includes 90% LiMn. 0.6 Fe 0.4 PO4 and 10% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0057] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 22 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 10 μm, and the specific surface area is 0.8 m². 2 / g.

[0058] Example 2

[0059] In this embodiment: the positive electrode active material in the positive electrode sheet includes 70% LiMn. 0.6 Fe 0.4 PO4 and 30% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0060] Among them, LiMn 0.6 Fe 0.4The median particle size of PO4 is 1.5 μm, and the specific surface area is 22 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 10 μm, and the specific surface area is 0.8 m². 2 / g.

[0061] Example 3

[0062] In this embodiment: the positive electrode active material in the positive electrode sheet includes 50% LiMn. 0.6 Fe 0.4 PO4 and 50% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0063] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 22 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 10 μm, and the specific surface area is 0.8 m². 2 / g.

[0064] Example 4

[0065] In this embodiment: the positive electrode active material in the positive electrode sheet includes 95% LiMn. 0.6 Fe 0.4 PO4 and 5% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0066] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 3 μm, and the specific surface area is 18 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1The median particle size of O2 is 12 μm, and the specific surface area is 0.7 m². 2 / g.

[0067] Example 5

[0068] In this embodiment: the positive electrode active material in the positive electrode sheet includes 80% LiMn. 0.6 Fe 0.4 PO4 and 20% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0069] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 0.8 μm, and the specific surface area is 24 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 8 μm, and the specific surface area is 1.3 m². 2 / g .

[0070] Example 6

[0071] In this embodiment: the positive electrode active material in the positive electrode sheet includes 60% LiMn. 0.6 Fe 0.4 PO4 and 40% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0072] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 4 μm, and the specific surface area is 15 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 6 μm, and its specific surface area is 1.4 m². 2 / g.

[0073] Comparative Example 1

[0074] In this comparative example: the positive electrode active material in the positive electrode sheet only includes LiMn. 0.6 Fe 0.4 PO4; the negative electrode active material is graphite; the electrolyte is LiPF6; the separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte, and separator are assembled to obtain a 20Ah lithium-ion battery.

[0075] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 22 m². 2 / g.

[0076] Comparative Example 2

[0077] In this comparative example: the positive electrode active material in the positive electrode sheet includes 40% LiMn. 0.6 Fe 0.4 PO4 and 60% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0078] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 22 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 10 μm, and the specific surface area is 0.8 m². 2 / g.

[0079] Comparative Example 3

[0080] In this comparative example: the positive electrode active material in the positive electrode sheet includes 30% LiMn. 0.6 Fe 0.4 PO4 and 70% LiNi 0.8 Co 0.1 Mn 0.1 O2; In the negative electrode, the negative electrode active material is graphite; The electrolyte in the electrolyte is LiPF6; The separator is a 9+2+2 separator (i.e., the thickness of the base film is 9μm, and the boehmite coatings on both sides of the base film are 2μm). The positive electrode, negative electrode, electrolyte and separator are assembled to obtain a 20Ah lithium-ion battery.

[0081] Among them, LiMn 0.6 Fe 0.4 The median particle size of PO4 is 1.5 μm, and the specific surface area is 22 m². 2 / g, LiNi 0.8 Co 0.1 Mn 0.1 The median particle size of O2 is 10 μm, and the specific surface area is 0.8 m². 2 / g.

[0082] The batteries assembled in Examples 1-3 and Comparative Examples 1-3 were subjected to specific capacity and safety performance tests. The specific capacity test process was as follows: the battery was charged to 4.2V at 0.2C under 25°C conditions, and then discharged to 2.5V at 0.2C for testing. Safety performance includes thermal runaway testing and overcharge testing. The thermal runaway test method is as follows: Following GB 38032-2020, the test subject is charged to 100% SOC, then charged at a 1C rate for 12 minutes. The heating device is immediately activated and continuously heated at its maximum power. Triggering is stopped and the heating device is turned off when thermal runaway occurs or the monitoring point temperature reaches 300℃. If fire or explosion occurs during heating or within one hour after heating, the test is terminated. The overcharge test method is as follows: Following GB 38032-2020, the battery is fully charged to 4.2V using a constant current and constant voltage method, then charged at a 1C rate to 4.62V or 115% SOC, and then charging is stopped. The test results are shown in Table 1 and Figures 1-3.

[0083] Table 1. Test results of specific capacity and safety performance in different embodiments and comparative examples.

[0084] Capacity (mAh / g) Maximum Thermal Runaway Temperature (°C) Thermal Runaway Onset Time (s) Thermal Runaway Phenomenon Overcharge Example 1: 145 479 1463 No fire, no explosion Pass Example 2: 153 515 1417 No fire, no explosion Pass Example 3: 16 158 11396 No fire, no explosion Pass Comparative Example 1: 140 468 1479 No fire, no explosion Pass Comparative Example 2: 170 671 1282 Fire, no explosion NG Comparative Example 3: 178 79 3915 Fire, explosion NG

[0085] In Examples 1-3 and Comparative Examples 1-3, the positive electrode active materials were composed of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in different ratios. The mass ratios of lithium nickel cobalt manganese oxide added in Examples 1-3 and Comparative Examples 1-3 were 10%, 30%, 50%, 0%, 60%, and 70%, respectively. As shown in Table 1, the specific capacity of the battery gradually increases with the increase in the proportion of lithium nickel cobalt manganese oxide in the positive electrode active material. Specific capacity directly affects the energy density of the battery; the higher the specific capacity, the higher the energy density. However, with the increase in the proportion of lithium nickel cobalt manganese oxide in the positive electrode active material, the highest temperature of thermal runaway also gradually increases, while the time of thermal runaway decreases, indicating that the thermal safety performance of the battery weakens with the increase in the proportion of lithium nickel cobalt manganese oxide in the positive electrode active material. Therefore, in order to achieve both high energy density and high safety performance, the mass ratio of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in the positive electrode active material needs to be controlled within a certain range.

[0086] The test results from Examples 1-3 and Comparative Example 1 show that when the mass percentage of lithium cobalt manganese oxide in the positive electrode active material formed by the compounding of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is no more than 50%, the highest thermal runaway temperature is below 600℃, the thermal runaway initiation time exceeds 1400s, and no fire or explosion occurs after thermal runaway. During overcharge testing, the batteries also did not catch fire or explode. This indicates that when the mass percentage of lithium cobalt manganese oxide in the positive electrode active material formed by the compounding of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is less than 50%, the battery safety performance is high and meets battery safety standards. Furthermore, since the positive electrode active materials of Examples 1-3 include both lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, compared to the positive electrode active material of Comparative Example 1 which only includes lithium manganese iron phosphate, the specific capacity of the battery is significantly higher. In other words, in embodiments 1-3 of this application, by simultaneously including lithium manganese iron phosphate and lithium nickel cobalt manganese oxide in the positive electrode active material, and controlling the ratio of the two within a certain range, the battery can have both high energy density and high safety performance.

[0087] The thermal runaway test curves for Example 2, Comparative Example 1, and Comparative Example 2 are shown in Figures 1, 2, and 3, respectively. Figure 1 shows the thermal runaway test curve for the positive electrode active material of 70% LMFP + 30% NCM (Example 2), with an onset time of 1417 s and a maximum thermal runaway temperature of 515℃. Figure 2 shows the thermal runaway test curve for the positive electrode active material of pure LMFP (Comparative Example 1), with an onset time of 1479 s and a maximum thermal runaway temperature of 468℃. Figure 3 shows the thermal runaway test curve for the positive electrode active material of 40% LMFP + 60% NCM (Comparative Example 2), with an onset time of 1282 s and a maximum thermal runaway temperature of 671℃. Comparative analysis shows that when the positive electrode active material is pure LMFP, the onset time of thermal runaway is the longest, the temperature is the lowest when thermal runaway occurs, and there is no fire or explosion during the process, indicating that pure LMFP has the highest thermal stability. As the amount of ternary compound in LMFP increases, the time to thermal runaway onset shortens and the maximum thermal runaway temperature increases, indicating that the thermal stability of the compound material system deteriorates with the increase of ternary compound content. Figure 3 shows that when the NCM doping content is 60%, an ignition phenomenon occurred during the thermal runaway test, indicating that the amount of compounded ternary compound should not be too high, as excessive amounts can easily lead to significant safety problems.

[0088] The test results from Examples 1-3 and Comparative Examples 2-3 show that when the mass percentage of lithium cobalt manganese oxide in the positive electrode active material formed by the compounding of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 60%, the highest thermal runaway temperature reaches 671°C, and fire occurs after thermal runaway. When the mass percentage of lithium cobalt manganese oxide is 70%, the highest thermal runaway temperature is 793°C, thermal runaway occurs much faster, and fire and explosion occur after thermal runaway. Furthermore, the batteries in Comparative Examples 2-3 all failed the overcharge test. These test results indicate that when the mass percentage of lithium cobalt manganese oxide in the positive electrode active material formed by the compounding of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide exceeds 50%, although the specific capacity and energy density of the battery increase, the battery safety decreases sharply. To ensure battery safety, the mass percentage of lithium cobalt manganese oxide in the positive electrode active material should not exceed 50%.

[0089] In addition, the rate discharge performance of the batteries in Examples 1-3 and Comparative Example 1 was tested. The test method was as follows: Rate performance: At 25°C, the batteries were charged to 4.2V with a current of 0.5C, and then discharged to 2.5V at different rates. The results are shown in Figure 4.

[0090] As shown in Figure 4, when the proportion of lithium nickel cobalt manganese oxide in the positive electrode active material is controlled below 50%, the rate discharge performance of the battery is basically the same. This indicates that the addition of lithium nickel cobalt manganese oxide can ensure the safety performance of the battery and maintain a certain high energy density, but will not affect the rate discharge performance or other performance characteristics of the battery.

Claims

1. A positive electrode active material, comprising lithium manganese iron phosphate and lithium nickel cobalt manganese oxide; wherein The mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is (50-95):(5-50); The chemical general formula of the lithium nickel cobalt manganese oxide is: LiNi a Co b Mn （ 1-a-b ） O2, 0.6≤a<1, 0 O2, 0.6≤a<1, 0 O2, 0.6≤a<1, 0 2. The positive electrode active material according to claim 1, wherein The median particle size D50 of the lithium iron manganese phosphate is 0.5 pm - 5 pm, the specific surface area is 14 m 2 / g - 25 m 2 / g.

3. The positive electrode active material according to claim 1 or 2, wherein The median particle size D50 of the lithium nickel cobalt manganese oxide is 4 μm-18 μm, the specific surface area is 0.2 m 2 / g - 1.5 m 2 / g.

4. The positive electrode active material according to any one of claims 1 to 3, wherein The lithium manganese iron phosphate has a chemical formula of LiMn 0.6 Fe 0.4 PO4.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The nickel cobalt manganese lithium has a chemical formula of LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2 and LiNi 0.9 Co 0.05 Mn 0.05 O2.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is 90:

10.

7. The positive electrode active material according to any one of claims 1 to 5, wherein The mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is 70:

30.

8. The positive electrode active material according to any one of claims 1 to 5, wherein The mass ratio of lithium manganese iron phosphate to lithium nickel cobalt manganese oxide is 50:

50.

9. A positive electrode slurry, comprising the positive electrode active material as described in any one of claims 1-8.

10. The positive electrode slurry according to claim 9 further comprises a positive electrode conductive agent, a positive electrode binder, and a positive electrode dispersant; wherein The mass ratio of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder and the positive electrode dispersant is (95-98):(0.5-2.5):(1-3):(0-1).

11. The positive electrode slurry of claim 10, wherein, The positive electrode conductive agent includes at least one of carbon nanotubes, graphene, and acetylene black.

12. The positive electrode slurry according to claim 10 or 11, wherein, The positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyacrylic acid.

13. A positive electrode sheet, comprising a positive electrode foil and a positive electrode active layer coated on the positive electrode foil; wherein, The positive electrode active layer is prepared using the positive electrode slurry as described in any one of claims 9-12, or the positive electrode active layer comprises the positive electrode active material as described in any one of claims 1-8.

14. The positive electrode sheet according to claim 13, wherein The positive electrode foil is a carbon-coated aluminum foil; The carbon-coated aluminum foil includes an aluminum foil and a carbon coating layer coated on the aluminum foil, wherein the thickness of the aluminum foil is 6μm-20μm, and the thickness of the carbon coating layer is greater than 0μm and less than or equal to 1μm.

15. A battery comprising a positive electrode as described in claim 13 or 14.

16. The battery according to claim 15, further comprising a negative electrode, an electrolyte, and a separator.

17. The battery of claim 16, wherein, The negative electrode sheet includes a negative electrode foil, a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder; The negative electrode foil is a copper foil or a copper mesh, and the thickness of the negative electrode foil is 4μm-12μm.

18. The battery of claim 16 or 17, wherein, The electrolyte includes an electrolyte, an organic solvent, and additives; The electrolyte is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate polycarbonate, and methyl ethyl carbonate; the additive includes at least one of ethylene carbonate, ethylene sulfate, methane disulfonate, lithium dioxalatoborate, and 1,3-propanesulfonyl lactone. The additive content accounts for 0.2%-1.5% of the total mass of the electrolyte.

19. The battery of any one of claims 16-18, wherein, The diaphragm includes a base membrane and a diaphragm coating applied to the base membrane; The base membrane is made of polypropylene or polyethylene; the membrane coating is made of at least one of aluminum oxide, boehmite, magnesium hydroxide, and barium sulfate. The thickness of the base film is 5μm-16μm, the thickness of the diaphragm coating is 0.5μm-5μm, and the tensile strength of the diaphragm is greater than 200MPa.

20. A vehicle comprising the battery as claimed in any one of claims 15-19.

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