Positive electrode active material, preparation method therefor, positive electrode sheet, battery, and electrical device

Abstract

The present application provides a positive electrode active material, a preparation method therefor, a positive electrode sheet, a battery, and an electrical device. The rate of change △d of the interplanar spacing of a characteristic peak of the positive electrode active material (104) satisfies: 0.05%≤△d≤0.5%, where △d=(dpre-dpost) / dpre×100%. dpre is the interplanar spacing of the characteristic peak of the positive electrode active material (104) measured by an X-ray diffractometer before cycling, and dpost is the interplanar spacing of the characteristic peak of the positive electrode active material (104) measured by an X-ray diffractometer at 45℃ after 80 cycles. Thus, the rate of change of the interplanar spacing of the positive electrode active material before and after cycling is small, indicating that the crystal structure stability of the positive electrode active material is good. During long-term cycling of a battery, the positive electrode active material is not prone to pulverization, and the cycle performance of the battery can be improved.

Description

Positive electrode active materials and their preparation methods, positive electrode sheets, batteries, and electrical equipment. Technical Field

[0001] This application relates to the field of batteries, specifically to positive electrode active materials and their preparation methods, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] With the booming development of the new energy vehicle industry, lithium-ion batteries have attracted much attention due to their high energy density and good cycle performance. As the component with the highest cost, the development of cathode active materials is also progressing rapidly. Multi-component cathode active materials, currently the highest-capacity commercially available materials, are widely used in power batteries. To prepare multi-component cathode active materials with higher energy density, better cycle performance, and superior safety, the development and application of high-nickel materials has become one of the mainstream development directions. However, the structural stability of high-nickel materials still needs to be improved. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art.

[0004] A first aspect of this application provides a positive electrode active material, said positive electrode active material comprising a compound represented by Formula I: Li 1+a (Ni x Co y Mn z G b )T c O2 formula I, where 0.01≤a≤0.1, 0.6≤x≤1, 0<y≤0.2, 0<z≤0.2, 0<b≤0.04, 0≤c≤0.03; G includes at least one of Al, Y, Zr, Ti, Ca, Na, Nb, Sn, Ta, Co, W, Er, La, Sb, Mg, Sr, Mo, Mn, Ce, Li, F, P, and T includes at least one of B, Al, Sr, Si, Nb, W, Ti, Zr, La, F, P; the characteristic peak interplanar spacing change rate Δd of the positive electrode active material (104) satisfies: 0.05%≤Δd≤0.5%, where Δd=(d 前 -d 后 ) / d 前 ×100%, d 前 d represents the interplanar spacing of the characteristic peaks of the positive electrode active material (104) as measured by X-ray diffraction before cycling. 后The interplanar spacing of the characteristic peak of the positive electrode active material (104) was measured by X-ray diffraction after 80 cycles at 45℃. The small change rate of the interplanar spacing before and after cycling indicates good crystal structure stability of the positive electrode active material. During long-term battery cycling, the positive electrode active material is less prone to pulverization, thus improving the battery's cycle performance.

[0005] According to some embodiments of this application, 0.05% ≤ Δd ≤ 0.3%. Therefore, the crystal structure stability of the positive electrode active material is good, which can improve the cycle performance of the battery.

[0006] According to some embodiments of this application, the cross-sectional porosity P of the positive electrode active material satisfies: 0.5% ≤ P ≤ 10%, and optionally, 1% ≤ P ≤ 5%. By keeping the cross-sectional porosity within the above range, it is beneficial for electrolyte wetting and capacity utilization. At the same time, it can improve the strength of the positive electrode active material, improve the structural stability of the positive electrode active material, and improve the cycle performance of the battery.

[0007] According to some embodiments of this application, the spherical breakage rate ΔB of the positive electrode active material satisfies: 0 < ΔB ≤ 60%, and optionally, 5% ≤ ΔB ≤ 40%. By keeping the spherical breakage rate within the above range, the strength of the positive electrode active material is improved, the structural stability of the positive electrode active material is improved, and the cycle performance of the battery is improved.

[0008] According to some embodiments of this application, 0.8 ≤ x ≤ 0.95. Therefore, the nickel content in the positive electrode active material is relatively high, thereby increasing the specific capacity of the positive electrode active material.

[0009] According to some embodiments of this application, G includes Al, Y, Zr, W, Sn, Ta, Sr, Mn, Na, Ba, and Li. This results in a more stable crystal lattice structure and a lower rate of change in interplanar spacing, leading to superior cycling performance.

[0010] The second aspect of this application provides a method for preparing the positive electrode active material provided in the first aspect of this application. The method includes: firstly mixing a nickel-cobalt-manganese precursor, a lithium source, and a first additive containing element G1 at a rotation speed of R1 to obtain a first mixture; the first additive includes at least one of an oxide containing element G1, a hydroxide containing element G1, and a carbonate containing element G1; secondly mixing the first mixture with a second additive containing element G2 at a rotation speed of R2 to obtain a second mixture, where R1 > R2; the second additive includes at least one of a sulfate containing element G2 and a phosphate containing element G2, where G = G1 + G2; firstly sintering the second mixture and then crushing it to obtain a sintered material; and finally mixing the sintered material with a third additive containing element T and then sintering it a second time at a temperature lower than that of the first sintering, followed by crushing to obtain the positive electrode active material. Therefore, high-speed physical mixing when adding the first additive allows the first additive to be evenly distributed on the material surface, and then evenly enters the crystal lattice after the first sintering, improving the lattice stability of the positive electrode active material; low-speed physical mixing when adding the second additive allows the second additive to remain on the material surface or at the grain boundaries. After washing away some of the second additive with water, pores can be generated on the material, forming some channels inside the material, which helps the electrolyte to wet the material, and thus helps the material to achieve its capacity.

[0011] According to some embodiments of this application, 1.1≤R1:R2≤8.

[0012] According to some embodiments of this application, the first sintering includes: heating the second mixture to T1℃ and holding it at that temperature for S1h, then further heating it to T2℃ and holding it at that temperature for S2h, and then cooling it to room temperature, wherein 250℃≤T1≤650℃, 1h≤S1≤5h, 650℃≤T2≤1000℃, and 6h≤S2≤12h. Thus, during the first sintering, the two holding times allow the lithium source and the first additive sufficient time to react with the precursor at a suitable temperature, simultaneously generating appropriate porosity and improving the particle strength of the positive electrode active material.

[0013] According to some embodiments of this application, the second sintering temperature is T3, the holding time is S3, and then it is cooled to room temperature, wherein 200℃≤T3≤500℃, 5h≤S3≤10h. This allows the second additive to better bond with the material surface, helping to improve the surface stability of the material.

[0014] According to some embodiments of this application, at least one of the following conditions is met: the volumetric particle size Dv100 of the first additive satisfies: 5μm≤Dv100≤50μm; the volumetric particle size Dv100 of the second additive satisfies: 50μm≤Dv100≤1000μm. Therefore, by ensuring the volumetric particle size of the first additive is within the above range, the first additive can better penetrate the material's crystal lattice, stabilizing the lattice and thus improving the material's cycle performance. By ensuring the volumetric particle size of the second additive is within the above range, the second additive tends to remain on the material surface or at grain boundaries. After water washing removes some of the second additive, pores can be created on the material, which is beneficial for electrolyte wetting and thus improves the material's capacity utilization.

[0015] According to some embodiments of this application, the method satisfies at least one of the following conditions: the G1 element includes at least one of Al, Y, Zr, Ti, Ca, Na, Nb, Sn, Ta, Co, W, Er, La, Sb, Mg, Sr, Mo, Mn, Ce, F, and P; optionally, the G1 element includes at least one of Al, Y, Zr, W, Sn, Ta, Sr, and Mn; the G2 element includes at least one of Al, Y, Zr, Ca, Na, Ba, Li, Mg, Sr, Mo, and Mn; optionally, the G2 element includes at least one of Al, Y, Na, Ba, and Li.

[0016] The third aspect of this application provides a positive electrode sheet, including the positive active material provided in the first aspect of this application or the positive active material prepared by the method provided in the second aspect of this application.

[0017] The fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.

[0018] The fifth aspect of this application provides an electrical device, including the battery provided in the fourth aspect of this application. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 shows a cross-sectional schematic diagram of the positive electrode active material in Embodiment 1 of this application under a scanning electron microscope.

[0021] Figure 2 shows a cross-sectional schematic diagram of the positive electrode active material in Embodiment 1 of this application after it is made into a positive electrode sheet under a scanning electron microscope.

[0022] Figure 3 shows a schematic flowchart of a method for preparing a positive electrode active material according to an embodiment of this application.

[0023] Figure labeling: 1 Pore active material; 2 Pores; 3 Cracks. Detailed Implementation

[0024] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0025] Multi-element cathode active materials have a layered structure, and the (104) characteristic peak is an important manifestation of this layered structure. The (104) characteristic peak is closely related to the electrochemical performance of multi-element cathode active materials. For example, a good peak shape and intensity mean that the cathode active material has a good lithium-ion transport channel and high crystal structure stability. During charging and discharging, lithium ions can be smoothly inserted and extracted, thus enabling the cathode active material to exhibit good rate performance, high reversible capacity, and good cycle performance. Among them, the peak spacing of the (104) characteristic peak is closely related to the stability of the layered structure. If the peak spacing changes significantly during battery charging and discharging, it will lead to the distortion or collapse of the layered structure, thereby affecting the electrochemical performance of the multi-element cathode active material and the cycle performance of the battery.

[0026] A first aspect of this application provides a positive electrode active material, said positive electrode active material comprising a compound represented by Formula I: Li 1+a (Ni x Co y Mn z G b )T c O2 formula I, where 0.01≤a≤0.1, 0.6≤x≤1, 0<y≤0.2, 0<z≤0.2, 0<b≤0.04, 0≤c≤0.03; G includes at least one of Al, Y, Zr, Ti, Ca, Na, Nb, Sn, Ta, Co, W, Er, La, Sb, Mg, Sr, Mo, Mn, Ce, Li, F, P, and T includes at least one of B, Al, Sr, Si, Nb, W, Ti, Zr, La, F, P; the characteristic peak interplanar spacing change rate Δd of the positive electrode active material (104) satisfies: 0.05%≤Δd≤0.5%, where Δd=(d 前 -d 后 ) / d 前 ×100%, d 前 d represents the interplanar spacing of the characteristic peaks of the positive electrode active material (104) as measured by X-ray diffraction before cycling. 后The interplanar spacing of the characteristic peaks of the positive electrode active material (104) was measured by X-ray diffraction after 80 cycles at 45°C.

[0027] The multi-element cathode active material proposed in this application exhibits a small change rate in interplanar spacing before and after cycling, indicating good crystal structure stability. During long-term battery cycling, the crystal structure can remain relatively stable, reducing internal stress accumulation and structural damage caused by structural changes, effectively slowing down battery capacity decay and improving battery cycle performance.

[0028] In order to test the rate of change of the interplanar spacing Δd of the (104) characteristic peak, this application obtains the interplanar spacing d of the (104) characteristic peak of the positive electrode active material by X-ray diffraction before the positive electrode active material is assembled into the battery. 前 The positive electrode active material is then prepared into a slurry and coated onto the positive electrode current collector to form a positive electrode sheet. The positive electrode sheet, negative electrode sheet, separator, and electrolyte are assembled into a battery. The battery is cycled for 80 cycles at 45°C. The battery is then disassembled, and the positive electrode active material on the positive electrode sheet is scraped off. The peak spacing d of the (104) characteristic peak of the positive electrode active material is measured using an X-ray diffractometer under the same test conditions. 后 Then, using the formula △d=(d 前 -d 后 ) / d 前 ×100%, calculate the rate of change of interplanar spacing Δd.

[0029] As an example, the positive electrode sheet includes a positive current collector and a positive active material layer located on the positive current collector. The positive active material layer includes the positive active material, binder, and conductive agent provided in the first aspect of this application.

[0030] As an example, the type and amount of adhesive are not specifically limited, and the adhesive may include one or more of polyvinylidene fluoride (PVDF), PVDF copolymers, or their modified (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.) derivatives.

[0031] As an example, the type and amount of conductive agent are not specifically limited, and the conductive agent may include one or more of acetylene black, conductive carbon black, carbon fiber (VGCF), carbon nanotubes (CNT), and Ketjen black.

[0032] As an example, the positive current collector can typically be a layer, and the positive current collector is typically a structure or component capable of collecting current. The positive current collector can be any material suitable for use as a positive current collector in an electrochemical energy storage device. For example, the positive current collector can be, but is not limited to, a metal foil, and more specifically, it can be, but is not limited to, nickel foil or aluminum foil.

[0033] The negative electrode sheet includes a negative current collector and a negative active material layer located on the surface of the negative current collector. The negative active material layer typically includes a negative active material. The negative active material is a conventional choice in the battery field, and its type and content are not specifically limited. It can be one or more of the following, including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium.

[0034] The graphite may include one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, and silicon alloy; the tin-based material may include one or more of elemental tin, tin oxide, and tin alloy.

[0035] The negative electrode current collector is typically a structure or component that collects current. This current collector can be any material suitable for use as a negative electrode current collector in a lithium-ion secondary battery. For example, it can be, but is not limited to, metal foil, and more specifically, copper foil. Furthermore, the negative electrode sheet can also be a lithium sheet.

[0036] As an example, separators are a common choice in the battery industry, and their types and contents are not specifically limited. They can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0037] As an example, the electrolyte is a common choice in the battery field, and its type and content are not specifically limited. It can be any electrolyte suitable for lithium secondary batteries in the field. For example, the electrolyte usually includes an electrolyte and a solvent. The electrolyte usually includes a lithium salt. More specifically, the lithium salt can be an inorganic lithium salt and / or an organic lithium salt, specifically including but not limited to one or more of LiPF6, LiBF4, LiN(SO2F)2 (abbreviated as LiFSI), LiN(CF3SO2)2 (abbreviated as LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (abbreviated as LiBOB), and LiBF2C2O4 (abbreviated as LiDFOB).

[0038] As an example, Δd can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.05% ≤ Δd ≤ 0.3%.

[0039] According to some embodiments of this application, the cross-sectional porosity P of the positive electrode active material satisfies: 0.5% ≤ P ≤ 10%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., or it can be any range of the above values. Therefore, when the rate of change of the interplanar spacing Δd of the characteristic peak (104) and the cross-sectional porosity P are within the above ranges, on the one hand, the crystal structure stability of the positive electrode active material is good, and the crystal structure of the positive electrode active material can remain relatively stable during battery charging and discharging, improving the overall cycle performance of the battery; on the other hand, the contact area between the electrolyte and the positive electrode is large, which is beneficial for the electrolyte to wet the positive electrode and maximize its capacity. According to some specific embodiments of this application, 1% ≤ P ≤ 5%.

[0040] In this application, the test method for cross-sectional porosity P is as follows: the positive electrode active material is cut open by ion cutting, and the cross-sectional morphology is photographed using a scanning electron microscope. Referring to Figure 1, multiple pores 2 exist on the cross-section of the positive electrode active material 1. The percentage of the total area of ​​pores on the cross-section to the total area of ​​the cross-section is calculated using intelligent analysis software for lithium-ion battery material microscopic images.

[0041] It should be noted that the cross-section referred to here is the porosity of the cross-section in the SEM image when the cross-sectional diameter is the same as the Dv50 of the positive electrode active material.

[0042] According to some embodiments of this application, the spheroidization rate ΔB of the positive electrode active material satisfies: 0 < ΔB ≤ 60%, for example, it can be 2%, 5%, 10%, 20%, 40%, 60%, etc., or a range of any of the above values. When the spheroidization rate of the positive electrode active material is within the above range, the strength of the positive electrode active material can be improved, the positive electrode active material can maintain its original morphology during battery charging and discharging, the cycle stability of the positive electrode active material can be improved, and the cycle performance of the battery can be improved. According to some specific embodiments of this application, 5% ≤ ΔB ≤ 40%.

[0043] In this application, the test method for the spherical breakage rate ΔB is as follows: The positive electrode active material proposed in this application is mixed with small-particle positive electrode active material in a mixing ratio of 1:9-9:1. The small-particle positive electrode active material is lithium-ion battery positive electrode material existing in single-crystal or polycrystalline forms, such as lithium nickel cobalt manganese oxide or lithium iron phosphate. The volume average particle size Dv50 of the small-particle positive electrode active material is 1μm-7μm. The positive electrode active material, conductive agent, and binder are mixed in a ratio of (90%-99%):(0.5%-6%):(0.5%-5%), slurried, coated, and dried to obtain a positive electrode sheet. The positive electrode sheet is pressed using a roller press to a compaction density of 3.5 g / cm³. 3The rolled positive electrode sheet was cut by ion cutting and the cross-sectional morphology was photographed by scanning electron microscopy. Referring to Figure 2, cracks were generated in some positive active material after rolling. Five images were taken at different locations under 1K conditions. The ratio of the number of cracked particles to the total number of particles in each image was calculated. The average value of the results of the five images was taken as ΔB.

[0044] As an example, 'a' can be 0.01, 0.05, 0.1, etc., or a range of any of the above values.

[0045] As an example, x can be 0.6, 0.7, 0.8, 0.9, 1, etc., or a range of any of the above values. According to some specific embodiments of this application, 0.8 ≤ x ≤ 0.95.

[0046] As an example, y can be 0.05, 0.1, 0.15, 0.2, etc., or a range of any of the above values.

[0047] As an example, z can be 0.05, 0.1, 0.15, 0.2, etc., or a range of any of the above values.

[0048] As an example, b can be 0.01, 0.02, 0.03, 0.04, etc., or a range of any of the above values.

[0049] As an example, c can be 0, 0.01, 0.02, 0.03, etc., or a range of any of the above values.

[0050] As an example, G may include one or more of Al, Y, Zr, W, Sn, Ta, Sr, Mn, Na, Ba, and Li.

[0051] The second aspect of this application provides a method for preparing the positive electrode active material provided in the first aspect of this application. The method includes: firstly mixing a nickel-cobalt-manganese precursor, a lithium source, and a first additive containing element G1 at a rotation speed of R1 to obtain a first mixture; the first additive includes at least one of an oxide containing element G1, a hydroxide containing element G1, and a carbonate containing element G1; secondly mixing the first mixture with a second additive containing element G2 at a rotation speed of R2 to obtain a second mixture, where R1 > R2; the second additive includes at least one of a sulfate containing element G2 and a phosphate containing element G2, where G = G1 + G2; firstly sintering the second mixture and then crushing it to obtain a sintered material; and finally mixing the sintered material with a third additive containing element T and then sintering it a second time at a temperature lower than that of the first sintering, followed by crushing to obtain the positive electrode active material. Therefore, high-speed physical mixing when adding the first additive can make the first additive evenly distributed on the surface of the material. After the first sintering, it can evenly enter the interior of the material lattice, thereby stabilizing the lattice. Low-speed physical mixing when adding the second additive can make the second additive stay on the surface of the material or at the grain boundary. After washing away some of the second additive with water, pores can be generated on the material, which is beneficial for the wetting of the electrolyte, thereby improving the performance and capacity of the material. After battery cycling, the interplanar spacing of the characteristic peak of the positive electrode active material (104) can be reduced, thereby improving the stability of the crystal structure of the positive electrode active material and improving the cycle performance of the battery.

[0052] The method is described in detail below. Referring to Figure 3, the method includes:

[0053] S10: The nickel-cobalt-manganese precursor, lithium source, and first additive containing element G1 are mixed for the first time at a rotation speed of R1 to obtain a first mixture. The first additive includes at least one of oxides, hydroxides, and carbonates containing element G1.

[0054] According to some embodiments of this application, a nickel-cobalt-manganese precursor, a lithium source, and a first additive containing G1 element are subjected to high-speed physical mixing to obtain a uniform first mixture. At least one of the oxides, hydroxides, and carbonates containing G1 element is subjected to high-speed physical mixing, which can make the first additive uniformly distributed on the material surface. After sintering, it can uniformly enter the interior of the material lattice, thereby improving the lattice stability of the positive electrode active material.

[0055] According to some embodiments of this application, 1.1≤R1:R2≤8. For example, it can be 1.1, 3, 5, 7, 8, etc., or it can be a range of any of the above values.

[0056] As an example, when using a high-speed mixer for mixing, 600rpm ≤ R1 ≤ 1000rpm. For example, it can be 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm, etc., or it can be any range of the above values.

[0057] According to some embodiments of this application, n (lithium element in lithium source): n (nickel cobalt manganese element in nickel cobalt manganese precursor) = (1.01-1.1):1, for example, it can be 1.01:1, 1.03:1, 1.05:1, 1.07:1, 1.1:1, etc., or it can be a range of any of the above values.

[0058] According to some embodiments of this application, the G1 element includes at least one selected from Al, Y, Zr, Ti, Ca, Na, Nb, Sn, Ta, Co, W, Er, La, Sb, Mg, Sr, Mo, Mn, Ce, F, and P.

[0059] According to some embodiments of this application, the G1 element includes at least one of Al, Y, Zr, W, Sn, Ta, Sr, and Mn.

[0060] According to some embodiments of this application, the nickel-cobalt-manganese precursor includes one or both of nickel-cobalt-manganese oxide and nickel-cobalt-manganese hydroxide.

[0061] According to some embodiments of this application, the lithium source includes one or more of lithium carbonate, aqueous lithium hydroxide, or anhydrous lithium hydroxide.

[0062] According to some embodiments of this application, the volumetric particle size Dv100 of the first additive satisfies: 5μm≤Dv100≤50μm.

[0063] S20: The first mixture and the second additive containing element G2 are mixed a second time at a rotation speed of R2 to obtain a second mixture, where R1 > R2. The second additive includes at least one of sulfate and phosphate containing element G2, where G = G1 + G2.

[0064] When the second additive is added, it is physically mixed at a low speed, which allows the second additive to remain on the surface of the material or at the grain boundaries. After some of the additive is washed away by water, some pores are created on the material, which is conducive to the wetting of the electrolyte and thus improves the capacity of the material.

[0065] As an example, when using a high-speed mixer for mixing, 200rpm ≤ R1 ≤ 600rpm. For example, it can be 200rpm, 300rpm, 400rpm, 500rpm, 600rpm, etc., or it can be any range of the above values.

[0066] According to some embodiments of this application, the volumetric particle size Dv100 of the second additive satisfies: 50μm≤Dv100≤1000μm. For example, it can be 50μm, 100μm, 300μm, 500μm, 700μm, 900μm, 1000μm, etc., or it can be a range of any of the above values.

[0067] According to some embodiments of this application, the G2 element includes at least one of Al, Y, Zr, Ca, Na, Ba, Li, Mg, Sr, Mo, and Mn.

[0068] According to some embodiments of this application, the G2 element includes at least one of Al, Y, Na, Ba, and Li.

[0069] According to some embodiments of this application, after the second mixing, the second mixture can be washed with water. The solid-liquid ratio of the water can be 1:1, and the washing time can be 3 min to 10 min. Then, the mixture is filtered using a funnel and dried in a vacuum drying oven.

[0070] S30: Perform a first sintering and crushing of the second mixture to obtain a sintered material.

[0071] According to some embodiments of this application, the second mixture is subjected to a first sintering in an oxygen atmosphere, and after sintering, it is crushed and sieved or directly sieved to obtain a sintered material.

[0072] According to some embodiments of this application, the first sintering includes: heating the second mixture to T1℃, holding it at that temperature for S1h, continuing to heat it to T2℃, holding it at that temperature for S2h, and then cooling it to room temperature, wherein 250℃≤T1≤650℃, 1h≤S1≤5h, 650℃≤T2≤1000℃, and 6h≤S2≤12h.

[0073] As an example, T1 can be 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, etc., or it can be a range of any of the above values.

[0074] As an example, S1 can be 1h, 2h, 3h, 4h, 5h, etc., or it can be a range of any of the above values.

[0075] As an example, T2 can be 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc., or it can be a range of any of the above values.

[0076] As an example, S2 can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc., or it can be a range of any of the above values.

[0077] By introducing two heat preservation processes during the first sintering process, the lithium source and the first additive have sufficient time to react with the precursor at the appropriate temperature, simultaneously generating appropriate porosity and improving the particle strength of the material.

[0078] S40: The first sintering material is mixed with a third additive containing element T, and then subjected to a second sintering at a temperature lower than that of the first sintering. The mixture is then crushed to obtain the positive electrode active material.

[0079] According to some embodiments of this application, the first sintering material is mixed with a third additive containing element T, and then sintered for the third time. The sintering atmosphere is air or oxygen. After sintering, the material is crushed and sieved or directly sieved to obtain the positive electrode active material.

[0080] According to some embodiments of this application, the temperature of the second sintering is T3, the holding time is S3, and then it is cooled to room temperature, satisfying 200℃≤T3≤500℃ and 5h≤S3≤10h.

[0081] As an example, T3 can be 200℃, 300℃, 400℃, 500℃, etc., or it can be a range of any of the above values.

[0082] As an example, it can be 5h, 6h, 7h, 8h, 9h, 10h, etc., or it can be a range of any of the above values.

[0083] In summary, the positive electrode active material and its preparation method proposed in this application have the following advantages:

[0084] ① The multi-element positive electrode active material proposed in this application has good crystal structure stability and a small change rate of interplanar spacing during battery charging and discharging, which can effectively slow down the capacity decay of the battery and improve the cycle performance of the battery.

[0085] ② The multi-element positive electrode active material proposed in this application has a suitable cross-sectional porosity, which is more conducive to the wetting of the positive electrode by the electrolyte and can improve the battery capacity.

[0086] ③ The positive electrode active material proposed in this application has high strength, is not easily broken during battery charging and discharging, has better structural stability, and can improve the cycle performance of the battery.

[0087] ④ The method for preparing positive electrode active materials proposed in this application uses high-speed physical mixing to add the first additive, which can make the first additive uniformly distributed on the surface of the material. After the first sintering, it enters the interior of the crystal lattice and plays a role in stabilizing the crystal lattice. Using low-speed physical mixing to add the second additive, the second additive can remain only on the surface of the material or at the grain boundary. After washing away some of the second additive with water, pores can be generated on the material, which is conducive to the wetting of the electrolyte and thus improves the capacity of the material.

[0088] ⑤ The method for preparing positive electrode active material proposed in this application involves heating the second mixture twice during the first sintering process, so that the lithium source, the first additive, and the second additive can react with the precursor at a suitable temperature for a sufficient time, thereby simultaneously generating appropriate pores and improving the particle strength of the material.

[0089] The third aspect of this application provides a positive electrode sheet, including the positive active material provided in the first aspect of this application or the positive active material prepared by the method provided in the second aspect of this application.

[0090] The fourth aspect of this application provides a battery including the positive electrode provided in the third aspect of this application.

[0091] The fifth aspect of this application provides an electrical device, including the battery provided in the fourth aspect of this application.

[0092] The embodiments of the present invention are described in detail below. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0093] Example 1

[0094] 1. Preparation of positive electrode active materials

[0095] Precursor (Ni) 0.8 Co 0.1 Mn 0.1(OH)2, lithium hydroxide, SrO2 and ZrO2 were physically homogenized at high speed using a high-speed mixer with R1 at 700 rpm to obtain the first mixture. The amounts of precursor, lithium hydroxide, Y2O3 and ZrO2 were such that n(Li):[n(Ni)+n(Co)+n(Mn)+n(Y)+n(Zr)]=1.05, n(Y):[n(Ni)+n(Co)+n(Mn)+n(Y)+n(Zr)]=0.008 and n(Zr):[n(Ni)+n(Co)+n(Mn)+n(Y)+n(Zr)]=0.003 in the positive electrode active material.

[0096] (2) The first mixture and Al2(SO4)3 were physically and uniformly mixed at a low speed using a high-speed mixer with R2 at 600 rpm to obtain the second mixture. The amount of Al2(SO4)3 was such that n(Al):[n(Ni)+n(Co)+n(Mn)+n(Y)+n(Zr)+n(Al)]=0.002 in the positive electrode active material.

[0097] (2) Under an oxygen atmosphere, the second mixture is sintered for the first time. The specific heating curve is as follows: heat up to 350°C in 2 hours, hold for 2 hours, heat up to 790°C in 5 hours, hold for 10 hours, and then start cooling. After sintering, crush and sieve or sieve directly to obtain a sintered material.

[0098] (3) Wash the calcined material with water at a solid-liquid ratio of 1:1 for 5 minutes, then filter it with a funnel, and finally dry it in a vacuum oven.

[0099] (4) The dried first-stage sintered material was mixed with boric acid at a ratio of [n(Ni)+n(Co)+n(Mn)+n(Y)+n(Zr)+n(Al)]:n(B)=1:0.005, and then subjected to a second sintering. The sintering atmosphere was air, the constant temperature was 300℃, and the constant temperature time was 10h. After sintering, the material was directly sieved to obtain the final positive electrode active material with the composition Li. 1.05 (Ni 0.8 Co 0.1 Mn 0.1 Y 0.008 Zr 0.003 Al 0.002 B 0.005 O2.

[0100] 2. Preparation of positive electrode sheet

[0101] Li, the positive electrode active material 1.05 (Ni 0.8 Co 0.1 Mn 0.1 Y 0.008 Zr0.003 Al 0.002 B 0.005 O2 9.5g, acetylene black 0.25g, and polyvinylidene fluoride (PVDF) 0.25g were mixed to form a positive electrode slurry. This slurry was coated onto aluminum foil and dried. It was then pressed into a diameter of 12mm and a thickness of 120μm under a pressure of 100MPa, and then dried in a vacuum drying oven at 120℃ for 12h to obtain the positive electrode sheet.

[0102] 3. Preparation of negative electrode sheet

[0103] The negative electrode uses a Li metal sheet with a diameter of 17 mm and a thickness of 1 mm.

[0104] 4. Separating membrane

[0105] The diaphragm uses a 25μm thick porous polyethylene membrane.

[0106] 5. Preparation of electrolyte

[0107] A 1.0 mol / L LiPF6 solution was used as the electrolyte, with an equal volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) as the solvent.

[0108] 6. Assemble the battery

[0109] The positive electrode, separator, negative electrode, and electrolyte are assembled into a 2025 type coin cell.

[0110] The preparation process of the positive electrode active materials in Examples 2-14 and Comparative Examples 1-4 is the same as that in Example 1, with the differences detailed in Tables 1 and 2.

[0111] Table 2

[0112] Performance testing

[0113] 1. Variation rate of interplanar spacing of characteristic peaks in (104) multi-element cathode active material

[0114] Before the positive electrode active material is assembled into the battery, the peak spacing d of the (104) characteristic peak of the positive electrode active material is obtained by X-ray diffraction. 前 The positive electrode active material is then prepared into a slurry and coated onto the positive electrode current collector to form a positive electrode sheet. The positive electrode sheet, negative electrode sheet, separator, and electrolyte are assembled into a battery. The battery is cycled for 80 cycles at 45°C. The battery is then disassembled, and the positive electrode active material on the positive electrode sheet is scraped off. The peak spacing d of the (104) characteristic peak of the positive electrode active material is measured using an X-ray diffractometer under the same test conditions. 后Then, using the formula △d=(d 前 -d 后 ) / d 前 ×100%, calculate the rate of change of interplanar spacing Δd.

[0115] Battery cycle conditions:

[0116] The battery sample was activated by charging and discharging twice at a current density of 20 mA / g, within a voltage range of 3.0V-4.3V. Using the activated battery sample, a specified number of charge-discharge cycles were performed at 45°C with a current density of 1C within a voltage range of 3.0-4.3V.

[0117] 2. Cross-sectional porosity P of multi-element cathode active materials

[0118] The positive electrode active material was cut by ion cutting, and the cross-sectional morphology was photographed using a scanning electron microscope. The percentage of the total area of ​​pores on the cross-section to the total area of ​​the cross-section was calculated using intelligent analysis software for lithium-ion battery material microscopic images.

[0119] 3. The spheroid splitting rate ΔB of the multi-component positive electrode active material

[0120] The positive electrode active material and small particles of positive electrode active material (8-series single crystal Li) 1.02 (Ni 0.8 Co 0.1 Mn 0.1 The positive electrode active material is mixed with oxygen (O2) at a ratio of 7:3. The volume average particle size (Dv50) of the small particles is 3.5 μm. The positive electrode active material, conductive carbon black, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed in a ratio of 97%:1%:0.5%:1.5%, slurryed, coated, and dried to obtain the positive electrode sheet. The compaction density of the positive electrode sheet is 3.5 g / cm³ using a roller press. 3 The positive electrode sheet after rolling was cut by ion cutting, and the cross-sectional morphology was photographed by scanning electron microscopy. Five images were taken at different locations under 1K conditions. The ratio of the number of cracked particles to the total number of particles in each image was calculated, and the average of the results of the five images was taken as ΔB.

[0121] 4. Capacity

[0122] Capacity testing conditions: The prepared coin cell samples were left to stand for 24 hours. The samples were charged at a current density of 20 mA / g until the cutoff voltage of 4.3 V. They were then charged at a constant voltage of 4.3 V for 30 minutes. Subsequently, they were discharged at a current density of 20 mA / g until the cutoff voltage of 3.0 V, and the discharge time was recorded.

[0123] The initial discharge specific capacity of the battery sample = current density × discharge time.

[0124] 5. Capacity retention rate after 80 cycles

[0125] Under the cycling conditions described above, 80 cycles were performed, and the discharge specific capacity for each charge-discharge cycle was obtained by using the current density and the discharge time of each cycle. The cycle performance of the battery sample with the discharge specific capacity after the 80th cycle was characterized by the high-temperature capacity retention rate.

[0126] Capacity retention after 80 cycles = (discharge specific capacity at week 80 / discharge specific capacity at week 1) × 100%.

[0127] The test results of the positive electrode active materials and batteries in Examples 1-14 and Comparative Examples 1-4 are shown in Table 3.

[0128] Table 3

[0129] As can be seen from the comparison between Examples 1-14 and Comparative Examples 1-4, the battery prepared using the positive electrode active material proposed in this application can have both high capacity and high cycle capacity retention rate. This indicates that by controlling the rate of change of the interplanar spacing of the positive electrode active material, a positive electrode active material with good crystal structure stability can be obtained, which can effectively slow down the capacity decay of the battery during battery cycling and improve the cycle performance of the battery.

[0130] As can be seen from the comparison between Examples 1-4 and Comparative Examples 2-4, in the process of preparing positive electrode active materials, by adding the first additive at high speed and adding the second additive at low speed, a positive electrode active material with stable crystal structure and small crystal interplanar spacing change rate can be obtained, thereby obtaining a battery with high capacity and high cycle capacity retention rate.

[0131] As can be seen from Examples 5-7, adding different types of first additives by high-speed stirring and adding different types of second additives by low-speed stirring can improve the lattice stability of the positive electrode active material and reduce the rate of change of interplanar spacing, thereby obtaining a battery with high capacity and high cycle capacity retention.

[0132] As can be seen from Examples 8-10, during the preparation of the positive electrode active material, the use of two heat preservation processes during the first sintering allows the lithium source, precursor, first additive, and second additive to react fully, reducing the rate of change in interplanar spacing of the positive electrode active material. At the same time, it gives the positive electrode active material appropriate porosity, improves the particle strength of the positive electrode active material, reduces the spheroidization rate of the positive electrode active material, and thus obtains a battery with high capacity and high cycle capacity retention.

[0133] As can be seen from Examples 11 and 12, by using the mixing method and sintering method of the first additive and the second additive proposed in this application, and by using the first additive and the second additive of different element types, positive electrode active materials with small crystal plane spacing change rate, moderate porosity and low spheroidization rate can be obtained, thereby obtaining batteries with high capacity and high cycle capacity retention rate.

[0134] As can be seen from Examples 13 and 14, when the nickel content in the precursor is different, the mixing method of the first additive and the second additive proposed in this application, as well as the sintering method, can also obtain a positive electrode active material with a small change rate of interplane spacing, moderate porosity, and low spheroidization rate, thereby obtaining a battery with high capacity and high cycle capacity retention.

[0135] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A positive electrode active material, comprising a compound represented by Formula I: Li 1+a (Ni x Co y Mn z G b )T c O2 type I, in, 0.01≤a≤0.1, 0.6≤x≤1, 0<y≤0.2, 0<z≤0.2, 0<b≤0.04, 0≤c≤0.03; G includes at least one of Al, Y, Zr, Ti, Ca, Na, Nb, Sn, Ta, Co, W, Er, La, Sb, Mg, Sr, Mo, Mn, Ce, Li, F, and P; T includes at least one of B, Al, Sr, Si, Nb, W, Ti, Zr, La, F, and P. The characteristic peak interplanar spacing variation rate Δd of the positive electrode active material (104) satisfies: 0.05% ≤ Δd ≤ 0.5%, where Δd = (d 前 -d 后 ) / d 前 ×100%, d 前 d represents the interplanar spacing of the characteristic peaks of the positive electrode active material (104) as measured by X-ray diffraction before cycling. 后 The interplanar spacing of the characteristic peaks of the positive electrode active material (104) was measured by X-ray diffraction after 80 cycles at 45°C.

2. The positive electrode active material according to claim 1, wherein, 0.05％≤△d≤0.3％。 3. The positive electrode active material according to claim 2, wherein, The cross-sectional porosity P of the positive electrode active material satisfies: 0.5% ≤ P ≤ 10%, and optionally, 1% ≤ P ≤ 5%.

4. The positive electrode active material according to claim 3, wherein, The sphericity ΔB of the positive electrode active material satisfies: 0 < ΔB ≤ 60%, and optionally, 5% ≤ ΔB ≤ 40%.

5. The positive electrode active material according to claim 1, wherein, 0.8≤x≤0.95。 6. The positive electrode active material according to claim 1, wherein, G includes at least one of Al, Y, Zr, W, Sn, Ta, Sr, Mn, Na, Ba, and Li.

7. A method for preparing the positive electrode active material according to any one of claims 1-6, wherein, include: The nickel-cobalt-manganese precursor, lithium source, and first additive containing G1 element are mixed for the first time at a rotation speed of R1 to obtain a first mixture. The first additive includes at least one of oxide containing G1 element, hydroxide containing G1 element, and carbonate containing G1 element. The first mixture and the second additive containing element G2 are mixed a second time at a rotation speed of R2 to obtain a second mixture, where R1 > R2. The second additive includes at least one of sulfate containing element G2 and phosphate containing element G2, where G = G1 + G2. The second mixture is subjected to a first sintering and crushing to obtain a sintered material; The first sintering material is mixed with a third additive containing element T, and then sintered a second time at a temperature lower than that of the first sintering. The mixture is then crushed to obtain the positive electrode active material.

8. The method according to claim 7, wherein, 1.1≤R1:R2≤8.

9. The method according to claim 8, wherein, The first sintering includes: heating the second mixture to T1℃, holding it at that temperature for S1h, continuing to heat it to T2℃, holding it at that temperature for S2h, and then cooling it to room temperature, wherein 250℃≤T1≤650℃, 1h≤S1≤5h, 650℃≤T2≤1000℃, and 6h≤S2≤12h.

10. The method according to claim 9, wherein, The second sintering temperature is T3, the holding time is S3, and then it is cooled to room temperature, satisfying 200℃≤T3≤500℃ and 5h≤S3≤10h.

11. The method according to claim 10, wherein, At least one of the following conditions must be met: The volumetric particle size Dv100 of the first additive satisfies: 5μm≤Dv100≤50μm; The volumetric particle size Dv100 of the second additive satisfies: 50μm≤Dv100≤1000μm.

12. The method according to claim 10, wherein, At least one of the following conditions must be met: The G1 element includes at least one of Al, Y, Zr, Ti, Ca, Na, Nb, Sn, Ta, Co, W, Er, La, Sb, Mg, Sr, Mo, Mn, Ce, F, and P; optionally, the G1 element includes at least one of Al, Y, Zr, W, Sn, Ta, Sr, and Mn. The G2 element includes at least one of Al, Y, Zr, Ca, Na, Ba, Li, Mg, Sr, Mo, and Mn. Optionally, the G2 element includes at least one of Al, Y, Na, Ba, and Li.

13. A positive electrode plate, wherein, The positive electrode active material includes the positive electrode active material according to any one of claims 1-6 or the positive electrode active material prepared by the method according to any one of claims 7-12.

14. A battery, wherein, Includes the positive electrode sheet as described in claim 13.

15. An electrical appliance, wherein, Includes the battery as described in claim 14.

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