Positive electrode active material and preparation method thereof, positive electrode plate, battery and electric equipment

Abstract

The invention provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery and electric equipment, the positive electrode active material comprises a body and a coating layer, the chemical formula of the body comprises Li < 1 + a > Ni < x > Mn < y > Co < z > M O < 2 >,-0.05 < = a < = 0.1, 0 < = b < = 0.05, 0 lt; xlt; 1, 0lt; yt; Yt; z is more than or equal to 0 and less than or equal to 0.03, and M comprises one or more of Zr, Y, W, Nb, Sr, Al, Mg, Mo, La, Er and Si; the coating layer comprises a cobalt element and a boron element, the thickness of the coating layer is 5-20 nm, and the penetration degree of the cobalt element penetrating into the body is 0.4-0.9. The positive electrode active material provided by the invention has excellent capacity and cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular, to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery, and an electric device. BACKGROUND

[0002] Under the background of advocating energy saving and emission reduction and reducing dependence on non-renewable resources, the electric vehicle industry has developed rapidly. The performance of electric vehicles is closely related to the performance of lithium ion batteries, and as a key component of lithium ion batteries, the positive electrode active material needs to have excellent performance. In the process of high-voltage charging and discharging, the crystal structure of the nickel-containing positive electrode active material is easily damaged, and the degree of nickel-lithium mixing is intensified, resulting in a decrease in battery performance. Cobalt coating as an important method of surface modification can significantly improve the structural stability of the positive electrode active material under high-voltage conditions. However, there are still many problems in the existing cobalt coating that need to be improved. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. The present application provides a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery, and an electric device. The positive electrode active material provided by the present application has excellent capacity and cycle performance.

[0004] The first aspect of the present application provides a positive electrode active material, the positive electrode active material comprising a body and a coating layer, the chemical formula of the body comprising: Li 1+a Ni x Mn y Co z M b O2, wherein -0.05≤a≤0.1, 0<b≤0.05, 0<x<1, 0<y<1, 0≤z≤0.03, -0.05≤c≤0.1, M comprises one or more of Zr, Y, W, Nb, Sr, Al, Mg, Mo, La, Er, Si; The coating layer comprises cobalt elements and boron elements, the thickness of the coating layer is 5-20 nm, and the penetration degree of the cobalt elements into the body is 0.4-0.9.

[0005] The positive electrode active material provided by the present application can greatly improve the structural stability of the positive electrode active material by coordinately controlling the thickness of the coating layer on the surface of the positive electrode active material and the penetration degree of the cobalt elements into the body, reduce the excessive aggregation of cobalt elements on the surface of the positive electrode active material particles, hinder the diffusion of lithium ions in the electrolyte during the charging and discharging process, and the coating layer is not easy to fall off, ensuring the capacity and structural stability of the positive electrode active material. In summary, the positive electrode active material provided by the present application has excellent capacity and cycle performance.

[0006] According to some embodiments of the present application, in the coating layer, the ratio of the amount of substance of the boron element and the cobalt element is (2.7-5.5):1; and / or, the particle strength of the positive electrode active material is 120 MPa-180 MPa.

[0007] According to some embodiments of the present application, the positive electrode active material satisfies at least one of the following conditions: M includes one or more of Zr, Y, Al; x=0.50-0.95; y=0.05-0.50; the thickness of the coating layer is 5 nm-10 nm; the penetration degree of the cobalt element into the body is 0.6-0.9.

[0008] According to some embodiments of the present application, the coating layer further includes an M1 element, the M1 element including one or more of Ti, Mg, Al, W, Zr, V, Sr; optionally, the ratio of the amount of substance of the M1 element and the cobalt element in the coating layer is (0.0001-0.0002):1.

[0009] According to some embodiments of the present application, the positive electrode active material satisfies one or more of the following conditions: the lithium-nickel mixing degree of the positive electrode active material is 0.5%-2.5%, optionally 0.5%-1.5%; the micro stress of the positive electrode active material is 0.01%-0.12%, optionally 0.01%-0.06%.

[0010] The second aspect of the present application provides a method for preparing the positive electrode active material provided in the first aspect of the present application, the method comprising: mixing a precursor, a lithium source, and optionally an M source, primary sintering, water washing, drying to obtain a primary sintered material, the precursor including a nickel element, a manganese element, and optionally a cobalt element; mixing a cobalt source and a boron source, and mixing with the primary sintered material, secondary sintering at 400°C-600°C to obtain the positive electrode active material.

[0011] The method for preparing the positive electrode active material provided in the present application constructs a loose and porous structure of particles by adding a water washing process, and then uses a solid phase coating technology to attach a composite of a cobalt source and a boron source to the surface of the positive electrode material. By using the low melting point characteristic of the boron source, after sintering and melting, the cobalt element is driven to penetrate along the pores of the secondary particles and is attached to the surface layer of the primary particles, so as to control the thickness of the coating layer on the surface of the positive electrode active material and the penetration degree of the cobalt element into the body, to maximize the improvement of the stability of the coating layer structure, and to improve the capacity and cycle performance of the positive electrode active material.

[0012] According to some embodiments of the present application, the method satisfies at least one of the following conditions: the temperature of the first sintering is 650-900°C; the time of the first sintering is 7-12h; the temperature of the water washing is 10-11°C; the time of the water washing is 1-1.5min; the cobalt source and the boron source are ball-milled and mixed for 4-8h; the mixed material after mixing of the cobalt source and the boron source has a median particle size D50 of 0.3-3μm; the time of the second sintering is 8-10h.

[0013] The third aspect of the present application provides a positive electrode tab, comprising the positive electrode active material provided in the first aspect of the present application or the positive electrode active material prepared by the method provided in the second aspect of the present application.

[0014] The fourth aspect of the present application provides a battery, comprising the positive electrode tab provided in the third aspect of the present application.

[0015] The fifth aspect of the present application provides a power consumption device, comprising the battery provided in the fourth aspect of the present application. DETAILED DESCRIPTION

[0016] Embodiments of the present application are described in detail below. The embodiments described below are exemplary and are intended to explain the present application, but cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product specification is used. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0017] The first aspect of the present application provides a positive electrode active material, the positive electrode active material comprising a body and a coating layer, the chemical formula of the body comprising: Li 1+a Ni x Mn y Co z M b O2, wherein -0.05≤a≤0.1, 0<b≤0.05, 0<c≤0.05, 0<x<1, 0<y<1, 0≤z≤0.03, M comprises one or more of Zr, Y, W, Nb, Sr, Al, Mg, Mo, La, Er, Si; the coating layer comprises cobalt elements and boron elements, the thickness of the coating layer is 5-20nm, and the penetration degree of the cobalt elements into the body is 0.4-0.9.

[0018] As an example, a can be -0.05, -0.02, 0, 0.02, 0.05, 0.08, 0.1 or a range between any two of the above values; b can be 0.01, 0.02, 0.03, 0.04, 0.05 or a range between any two of the above values; c can be 0.01, 0.02, 0.03, 0.04, 0.05 or a range between any two of the above values; z can be 0, 0.01, 0.02, 0.03 or a range between any two of the above values.

[0019] In the present application, the coating layer refers to a thin solid solution layer on the surface of the secondary particle, which mainly contains boron and cobalt elements.

[0020] The positive electrode active material provided in the present application can greatly improve the structural stability of the positive electrode active material by coordinately controlling the thickness of the coating layer on the surface of the positive electrode active material and the penetration degree of cobalt elements into the bulk, so that the structure of the positive electrode active material is not damaged during the cycling process, and the lithium-nickel mixing degree is reduced. Within the above range of the coating layer thickness and the penetration degree of cobalt elements into the bulk, the grain boundary bonding force can be enhanced, the intergranular cracks caused by volume change during the cycling process of the positive electrode active material can be reduced, and too much cobalt gathered on the surface of the positive electrode active material can be reduced to hinder the diffusion of lithium ions in the electrolyte during the charging and discharging process. The coating layer is not easy to fall off, and the coating layer will not be too thick to occupy too much mass of the positive electrode active material, so as to ensure the capacity and structural stability of the positive electrode active material.

[0021] According to some embodiments of the present application, M includes one or more of Zr, Y, W, Nb, Sr, Al, Mg, Mo, La, Er, Si, and according to some other embodiments of the present application, M includes one or more of Zr, Y, Al. Thus, the above-mentioned doping elements can further stabilize the structure of the positive electrode active material, reduce the lithium-nickel mixing degree, and further improve the capacity and cycling performance of the positive electrode active material.

[0022] According to some embodiments of the present application, in the chemical formula of the positive electrode active material, 0 < x < 1, as an example, x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or a range between any two of the above values, and according to some other embodiments of the present application, x = 0.50-0.95. Thus, within the above range of nickel content, the capacity and cycling performance of the positive electrode active material can be improved.

[0023] According to some embodiments of the present application, 0 < y < 1. For example, y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or a range between any two of the above values. According to some other embodiments of the present application, y = 0.05-0.50. In this way, the cycle performance of the positive electrode active material can be further improved, and the cost of the positive electrode active material can be reduced.

[0024] It can be understood that the chemical formula of the positive electrode active material and the subscript of each element can be measured by ICP method (inductively coupled plasma technology). The instrument used is PE Optima 7000DV, and the test conditions are that 0.1 g of sample is completely dissolved in a mixed acid solution of 3 mL of HNO3+9 mL of HCl, and diluted to 250 mL for testing.

[0025] According to some embodiments of the present application, the thickness of the coating layer is 5 nm-20 nm. For example, the thickness of the coating layer can be 5 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, or a range between any two of the above values. According to some other embodiments of the present application, the thickness of the coating layer is 5 nm-10 nm. In this way, by controlling the thickness of the coating layer within the above range, the excessive cobalt elements gathered on the surface of the positive electrode active material particles can be reduced to hinder the diffusion of lithium ions in the electrolyte during the charging and discharging process, and the coating layer is not too thick to easily fall off, thereby ensuring the capacity and structural stability of the positive electrode active material.

[0026] According to some embodiments of the present application, the penetration degree of the cobalt elements into the body is 0.4-0.9, for example, it can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or a range between any two of the above values. According to some other embodiments of the present application, the penetration degree of the cobalt elements into the body is 0.6-0.9. It can be understood that the penetration degree of the cobalt elements into the body = 2f / d, f is the depth of the cobalt elements penetrating into the body, and d is the average diameter of the positive electrode active material, which can be the median particle size D50 of the positive electrode active material. In this way, by controlling the penetration degree of the cobalt elements into the body within the above range, the excessive cobalt gathered on the surface of the positive electrode active material particles can be reduced to hinder the diffusion of lithium ions in the electrolyte during the charging and discharging process, the coating layer is not easy to fall off, thereby ensuring the capacity and structural stability of the positive electrode active material, and at the same time, the cationic disordering on the surface of the crystal grains can be reduced, the crystal order degree can be improved, the layered structure can be stabilized, the micro stress can be reduced, the intergranular cracks caused by volume change of the positive electrode active material during high-voltage charging and discharging can be prevented, and the cycle life at high voltage can be improved.

[0027] It can be understood that the depth of the cobalt elements penetrating into the body and the thickness of the coating layer can be measured by SEM-EDS.

[0028] According to some embodiments of the present application, the ratio of the amount of substance of the boron element to the cobalt element in the coating layer is (2.7-5.5):1. For example, the ratio of the amount of substance of the boron element to the cobalt element can be 2.7:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or a range formed by any two of the above values. Controlling the ratio of the amount of substance of the two elements within the above range can reduce the lithium-nickel mixing degree and the micro stress of the positive electrode active material, reduce the defect degree and stabilize the structure. In the charging and discharging cycle process, the positive electrode active material particles are not easy to break, and thus the capacity and the cycle performance are more excellent.

[0029] According to some embodiments of the present application, the particle strength of the positive electrode active material is 120-180 MPa. For example, the particle strength of the positive electrode active material can be 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa or a range formed by any two of the above values. The particle strength of the positive electrode active material is high, and in the cycle process of the positive electrode active material, the positive electrode active material is not easy to break or collapse due to expansion and contraction, the structural stability of the positive electrode active material is improved, and the cycle performance of the positive electrode active material is improved.

[0030] It can be understood that the particle strength of the positive electrode active material can be determined by using a micro compression tester (MCT-210) of Shimadzu.

[0031] According to some embodiments of the present application, the coating layer further comprises an M1 element, and the M1 element comprises one or more of Ti, Mg, Al, W, Zr, V and Sr. Adding the above elements to the coating layer can further reduce the defect degree of the positive electrode active material, improve the structural stability, and improve the capacity and the cycle performance of the positive electrode active material.

[0032] According to some embodiments of the present application, the ratio of the amount of substance of the M1 element to the cobalt element in the coating layer is (0.0001-0.0002):1. For example, the ratio of the amount of substance of the two can be 0.0001, 0.00015, 0.0002 or a range formed by any two of the above values. Controlling the ratio of the amount of substance of the two within the above range can further reduce the defect degree of the positive electrode active material, improve the structural stability, and the M1 element will not be too much to affect the capacity of the positive electrode active material, and further improve the capacity and the cycle performance of the positive electrode active material.

[0033] According to some embodiments of the present application, the lithium-nickel mixing degree of the positive electrode active material is 0.5%-2.5%, for example, it can be 0.5%, 1%, 1.2%, 1.4%, 1.5%, 1.7%, 1.9%, 2%, 2.5% or a range composed of any two of the above values. According to other embodiments of the present application, the lithium-nickel mixing degree of the positive electrode active material is 0.5%-1.5%. Thus, the low lithium-nickel mixing degree of the positive electrode active material can reduce the capacity attenuation caused by the fracture of the positive electrode active material grain during high-voltage charging and discharging, and improve the cycle life of the positive electrode active material.

[0034] According to some embodiments of the present application, the micro stress of the positive electrode active material is 0.01%-0.12%, for example, it can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.12% or a range composed of any two of the above values. According to other embodiments of the present application, the micro stress of the positive electrode active material is 0.01%-0.06%. Thus, the low micro stress of the positive electrode active material has low defects and a more stable structure, which can further improve the cycle performance of the positive electrode active material.

[0035] It can be understood that the lithium-nickel mixing degree and the micro stress of the positive electrode active material can be determined by X-ray diffraction test and refinement, wherein the XRD test scanning range is 10°≤2θ≤90°, the scanning speed is 5° / min, the Topas refinement software is used, and the Pawley full spectrum fitting method is used.

[0036] According to some embodiments of the present application, the median particle size D50 of the positive electrode active material is 5μm-18μm. For example, the median particle size D50 of the positive electrode active material can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or a range composed of any two of the above values. According to other embodiments of the present application, the median particle size D50 of the positive electrode active material is 7μm-15μm. Thus, the too large particle size can prolong the lithium ion diffusion path, reduce the capacity and rate performance of the material; the too small particle size can easily cause particle agglomeration, increase the processing difficulty, and the too small particle size can increase the interface impedance and aggravate the side reaction, affecting the cycle stability.

[0037] It can be understood that the median particle size D50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50%, i.e. the volume content of particles with a particle size greater than this particle size accounts for 50% of all particles, and the volume content of particles with a particle size less than this particle size also accounts for 50% of all particles. The above particle size value can be determined by instruments and methods known in the art, for example, refer to standard GB / T 19077 2016, using a laser particle size analyzer (e.g. Malvern Master Size 3000).

[0038] According to some embodiments of the present application, the specific surface area of the positive electrode active material is 0.45m 2 / g-1.50m 2 / g. For example, the specific surface area of the positive electrode active material can be 0.45m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or a range composed of any two of the above values. According to some other embodiments of the present application, the specific surface area of the positive electrode active material is 0.60m 2 / g-1.20m 2 / g. Controlling the specific surface area of the positive electrode active material within the above range, the larger the specific surface area, the more active sites on the material surface, and the more entrances for lithium ion intercalation and deintercalation, thereby improving the initial capacity, which can shorten the lithium ion diffusion path and accelerate the charging and discharging rate. A large specific surface area can provide a porous and loose structure, which is beneficial for cobalt to penetrate along the pores and improve the stability of the material at high voltage. It can also reduce the dissolution of surface metal ions into the electrolyte when the specific surface area is too large, thereby improving the cycle life of the positive electrode active material at high voltage.

[0039] According to some embodiments of the present application, the grain diameter of the positive electrode active material is 790nm-830nm, for example, it can be 790nm, 800nm, 810nm, 820nm, 830nm or a range composed of any two of the above values. In this way, the grain diameter of the positive electrode active material is moderate, which can further improve the stability of the positive electrode active material.

[0040] In a second aspect, the present application provides a method for preparing the positive electrode active material. According to an embodiment of the present application, the method comprises: S1: mixing a precursor, a lithium source, and optionally an M source, once sintering, water washing, drying to obtain a once sintered material, wherein the precursor comprises nickel element, manganese element, and optionally cobalt element; According to some embodiments of the present application, the precursor is a low-cobalt or cobalt-free precursor, the precursor can be a self-produced or commercially available precursor, the phase of the precursor is an oxide or a hydroxide, and the chemical formula can be Ni x Mn y Co z (OH)2; wherein 0 < x < 1, 0 < y < 1, 0 ≤ z ≤ 0.03; wherein the lithium source is one of lithium hydroxide or lithium carbonate; the M source refers to a solid compound for introducing a doping element M into the positive electrode active material, which comprises a metal oxide or a salt, and the doping element is used to enter the crystal structure or the grain boundary in the once sintering; the once sintering atmosphere can be oxygen.

[0041] According to some embodiments of the present application, the temperature of the once sintering is 650-900°C. For example, it can be 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or a range composed of any two of the above values. Controlling the temperature of the once sintering within the above range can make the once sintered material doped and solidified with crystal growth, facilitate the formation of a porous structure, and increase the specific surface area of the once sintered material.

[0042] According to some embodiments of the present application, the time of the once sintering is 7-12h. For example, it can be 7h, 8h, 9h, 10h, 11h, 12h, or a range composed of any two of the above values. In this way, the reaction of the M source and the precursor can be promoted to be more sufficient, which is conducive to the growth of the crystal.

[0043] According to some embodiments of the present application, the temperature of the water washing is 10-11°C. The water washing temperature refers to the temperature of the water used for water washing. The water washing temperature can be 10°C, 10.5°C, 11°C, or a range composed of any two of the above values. In this way, the water washing facilitates the once sintered material to form a loose and porous structure, which is conducive to the subsequent coating, and the cobalt element penetrates into the interior of the body along the porous structure to form a positive electrode active material with a required penetration depth of the cobalt element.

[0044] According to some embodiments of the present application, the time of the water washing is 1-1.5min. For example, it can be 1min, 1.2min, 1.4min, 1.5min, or a range composed of any two of the above values. In this way, it is further conducive to the once sintered material to form a loose and porous structure.

[0045] According to some embodiments of the present application, the washing agent for water washing is deionized water, the mass ratio of the primary sintering material to water is 2.0-2.5, which can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 or a range formed by any two of the above values; the stirring rate is 150-200 rpm, for example, it can be 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm or a range formed by any two of the above values.

[0046] S2: mixing the cobalt source and the boron source, and mixing with the primary sintering material, secondary sintering at 400-600°C to obtain the positive electrode active material.

[0047] According to some embodiments of the present application, a specific proportion of cobaltous hydroxide and boric acid is crushed, mixed uniformly by ball milling, or a cobaltous hydroxide and boric acid compound is directly purchased, and a soybean milk machine is used to crush to obtain an additive with a suitable particle size.

[0048] According to some embodiments of the present application, the median particle size D50 of the mixture after mixing the cobalt source and the boron source is 0.3-3 μm, for example, it can be 0.3 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or a range formed by any two of the above values, thereby, during subsequent secondary sintering, the boron source is melted by sintering, and the cobalt element is penetrated along the pores of the secondary particles, so as to control the thickness of the surface coating layer of the positive electrode active material and the penetration degree of the cobalt element.

[0049] According to some embodiments of the present application, the ball milling mixing rate is 800 rpm, and the mixing time is 4-8 h, for example, the mixing time can be 4 h, 5 h, 6 h, 7 h, 8 h or a range formed by any two of the above values, and the ball-to-material ratio is 1:1, thereby facilitating the formation of a uniform coating agent containing cobalt and boron.

[0050] According to some embodiments of the present application, when the coating layer contains M1 elements, an M1 source is also added during ball milling mixing.

[0051] According to some embodiments of the present application, the secondary sintering temperature is 400-600°C, for example, it can be 400°C, 450°C, 500°C, 550°C, 600°C or a range formed by any two of the above values, controlling the secondary sintering temperature within the above range is sufficient to make the boron source form a melt, drive the cobalt element to penetrate along the pores of the secondary particles, and adhere to the surface layer of the primary particles, so as to control the thickness of the surface coating layer of the positive electrode active material and the penetration degree of the cobalt element, maximize the improvement of the stability of the coating layer structure, and improve the capacity and cycle performance of the positive electrode active material.

[0052] According to some embodiments of the present application, the time of the secondary sintering is 8h-10h. For example, it can be 8h, 9h, 10h or a range between any two of the above values, so that the cobalt element can be driven into the inside of the positive electrode active material body by boron, and a positive electrode active material with a required thickness of the surface coating layer and a required penetration degree of the cobalt element into the body is obtained.

[0053] According to some embodiments of the present application, the secondary sintering atmosphere is oxygen.

[0054] In summary, the preparation method of the positive electrode active material proposed in the present application constructs a loose and porous structure of the particles by adding a water washing process, and then uses a solid phase coating technology to attach the composite of the cobalt source and the boron source to the surface of the positive electrode material. By using the low melting point characteristic of the boron source, the cobalt element is driven to penetrate along the pores of the secondary particles after sintering and melting, and is attached to the surface layer of the primary particles, so as to control the thickness of the surface coating layer of the positive electrode active material and the penetration degree of the cobalt element into the body, maximize the stability of the coating layer structure, and improve the capacity and cycle performance of the positive electrode active material. In addition, the cobalt coating sintering temperature (the second sintering temperature) is low, and the production cost is low.

[0055] In a third aspect of the present application, a positive electrode tab is proposed. According to embodiments of the present application, the positive electrode tab includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material obtained by the method described in the second aspect of the present application.

[0056] According to embodiments of the present application, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material described above, wherein the positive electrode current collector can be a metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector), for example, the positive electrode current collector can be an aluminum foil.

[0057] According to some embodiments of the present application, the positive electrode active material layer can optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, or a fluorine-containing acrylic ester resin.

[0058] According to some embodiments of the present application, the positive electrode active material layer can optionally include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0059] According to some embodiments of the present application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0060] It should be noted that the features and advantages described above for the positive electrode active material and the preparation method thereof are also applicable to the positive electrode sheet, which will not be described here again.

[0061] In a fourth aspect of the present application, a battery is provided. According to embodiments of the present application, the battery comprises the above-mentioned positive electrode sheet.

[0062] As an example, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator film, which is located between the positive electrode sheet and the negative electrode sheet. During the charging and discharging process of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator film is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the short circuit of the positive and negative electrodes, while allowing ions to pass through.

[0063] According to embodiments of the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, wherein the negative electrode current collector can be a metal foil or a composite current collector (a metal material can be arranged on a polymer substrate to form a composite current collector), for example, the positive electrode current collector can be a copper foil.

[0064] According to some embodiments of the present application, the negative electrode active material can comprise at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate, etc.

[0065] According to some embodiments of the present application, the negative electrode active material layer can further optionally comprise a conductive agent. The conductive agent can comprise at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene or carbon nanofibers.

[0066] According to some embodiments of the present application, the negative electrode active material layer can further optionally comprise other auxiliary agents, such as thickening agents (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0067] According to some embodiments of the present application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, and the binder, in a solvent (e.g., deionized water) to form a negative electrode slurry, coating the negative electrode slurry on a negative electrode current collector, and then performing drying, cold pressing, and other processes to obtain the negative electrode sheet.

[0068] According to yet some embodiments of the present application, the negative electrode sheet can also be a lithium metal sheet.

[0069] According to yet some embodiments of the present application, the type of the separator film is not particularly limited, and any known porous structure separator film with good chemical stability and mechanical stability can be selected. For example, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0070] According to yet some embodiments of the present application, the type of the electrolyte is not particularly limited, and can be selected according to the needs. For example, the electrolyte can be in a gel state or a full solid state. According to some specific embodiments of the present application, the electrolyte uses an electrolyte solution, which includes a lithium salt and a solvent.

[0071] According to some specific embodiments of the present application, the lithium salt can include at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethylsulfonate, or lithium bis(trifluoromethylsulfonyl)imide.

[0072] According to some specific embodiments of the present application, the solvent can include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, or diethyl sulfone.

[0073] In some embodiments of the present application, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature or low-temperature performance of the battery, etc.

[0074] It should be noted that the features and advantages described above for the positive electrode sheet also apply to the battery, and will not be repeated here.

[0075] In a fifth aspect, the present application provides a power consuming device. According to embodiments of the present application, the power consuming device comprises the battery as described above. According to embodiments of the present application, the power consuming device can include, but is not limited to, a mobile phone, a notebook computer, an electric vehicle, etc.

[0076] It should be noted that the features and advantages described above for the battery also apply to the power consuming device, which will not be repeated here.

[0077] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are intended to explain the present application only, and should not be understood as limiting the present application. In the embodiments, unless specific techniques or conditions are mentioned, the techniques or conditions described in the literature in the art or according to the product manual are used. The reagents or instruments used, unless the manufacturer is mentioned, are all conventional products that can be obtained commercially.

[0078] Example 1 The cobaltous hydroxide and boric acid were crushed and mixed uniformly by ball milling to obtain a mixed additive, the D50 of the mixed material was 0.87 μm, and the molar ratio of boron element and cobalt element was 5.45:1.

[0079] The Ni 0.75 Mn 0.25 The (OH)2, LiOH and ZrO2 were dry mixed according to a molar ratio of 1:1.04:0.002.

[0080] The mixture was subjected to primary sintering in a muffle furnace under an oxygen atmosphere, the sintering temperature was 800℃, the constant temperature time was 7h, and the primary sintered material was obtained after crushing with a colloid mill and sieving.

[0081] (3) The primary material was washed with water, the mass ratio of the primary sintered material to the aqueous solution was 2.4, the stirring rate was 180 rpm, the water washing temperature was 11℃, the water washing time was 1.5 min, and the washed and dried material was obtained after suction filtration and drying.

[0082] (4) The washed and dried material was mixed with the cobalt coating agent according to a molar ratio of 1:0.02 to obtain a coated material.

[0083] (5) The coated material was subjected to secondary sintering in a muffle furnace under an oxygen atmosphere, the sintering temperature was 450℃, the constant temperature sintering time was 8h, and the positive electrode active material was obtained after cooling, crushing and sieving.

[0084] The remaining examples and comparative examples differ from example 1 in that the data of the positive electrode active material of each example and comparative example are shown in the following table, wherein the elemental ratio of the positive electrode active material chemical formula, the amount and ratio of the coating element are changed, and the corresponding amount and type of the added element are adjusted. In examples 2-4, the amount of boron element is constant, and the amount of cobalt element is adjusted.

[0085] Table 1

[0086] Performance test In the above examples and comparative examples, the relevant parameters are tested by the following methods: XRD test: The positive electrode active material prepared in the examples and comparative examples is subjected to XRD test, and the scanning range of XRD test is 10°≤2θ≤90°, and the scanning speed is 5° / min.

[0087] The depth of cobalt element penetration into the body and the thickness of the coating layer can be measured by SEM-EDS. The penetration degree of cobalt element into the body = 2f / d, f is the depth of cobalt element penetration into the body, and d is the average diameter of the positive electrode active material.

[0088] The particle strength of the positive electrode active material is determined by using a micro compression tester (MCT-210) of Shimadzu.

[0089] The grain diameter, lithium-nickel mixing degree and micro stress are determined by the following method: X-ray diffraction method test and refinement, wherein the scanning range of XRD test is 10°≤2θ≤90°, the scanning speed is 5° / min, and Topas refinement software and Pawley full spectrum fitting method are used.

[0090] The median particle size D50 of the positive electrode active material is determined by referring to standard GB / T19077 2016, and using a laser particle size analyzer (such as Malvern Master Size 3000).

[0091] The specific surface area of the positive electrode active material is determined by using a static gas adsorption method by TriStar II Plus 3030 specific surface area tester of Micromeritics.

[0092] Table 2

[0093] The electrochemical performance of the positive electrode active material is tested by using a CR2025 type button lithium ion battery. The preparation process of the CR2025 button battery is as follows: Preparation of positive electrode sheet: the positive electrode active material, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed with N-methyl pyrrolidone (NMP) in a mass ratio of 95:2.5:2.5 to form a uniform slurry, which was coated on an aluminum foil and dried at 120°C for 12 h, then punched and formed into a positive electrode sheet with a diameter of 12 mm and a thickness of 3.2 mm using a pressure of 100 MPa, wherein the loading amount of the positive electrode material was 15.5 mg / cm 2 .

[0094] Battery assembly: the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte were assembled into a CR2032 button cell in an argon-filled glove box with water content and oxygen content less than 5 ppm, and then left to stand for 6 h. The negative electrode sheet was a lithium metal sheet with a diameter of 15.8 mm and a thickness of 1 mm; the separator was a polypropylene microporous membrane (Celgard2325) with a thickness of 25 μm; and the electrolyte was an equal amount of mixture of 1 mol / L LiPF6, ethylene carbonate (EC) and diethyl carbonate (DEC).

[0095] Electrochemical performance test: 0.1C discharge capacity test: the electrochemical performance of the CR2025 button cell was tested by using a Shenzhen Xinwei battery test system, the charge and discharge voltage range was controlled to be 2.5-4.45 V, the button cell was charged and discharged at 0.1C for 1 cycle at a constant temperature of 25°C, and the capacity of the positive electrode active material was evaluated.

[0096] 80-week high-temperature cycle retention rate test: the electrochemical performance of the CR2025 button cell was tested by using a Shenzhen Xinwei battery test system, the charge and discharge voltage range was controlled to be 2.5-4.45 V, the button cell was charged and discharged at 0.1C for 2 cycles at a constant temperature of 45°C, and then charged and discharged at 1C for 80 cycles, and the high-temperature cycle capacity retention rate of the positive electrode material was evaluated.

[0097] The test results of the batteries in the examples and comparative examples are shown in Table 3.

[0098] Table 3

[0099] From Table 1-Table 3, in Example 3 and Example 4, the content of element B is low or high, the thickness of cobalt coating layer and the penetration degree of cobalt element are close to the upper and lower limits, the lithium-nickel mixing degree and micro stress are increased compared with Example 1 and Example 2, the capacity and high-temperature cycle are worse than Example 1 and Example 2, the positive active material coating layer of Comparative Example 1 only has cobalt element, the positive active material coating layer of Comparative Example 2 only has element B, the thickness of cobalt coating layer and the penetration degree of cobalt element are out of the limited range, the lithium-nickel mixing degree and micro stress are significantly increased, the capacity and high-temperature cycle are significantly deteriorated, which shows that in the B / Co composite additive, element B has the effect of enhancing the melting of cobalt element and driving the penetration of cobalt element within a certain dosage range, and when the penetration degree of cobalt element in the secondary particles increases, the degree of fracture and defect of the positive active material grain in the high-voltage charging and discharging process is reduced, the structural stability is improved, which is beneficial to the capacity and high-temperature cycle performance, however, the penetration of B / Co element is closely related to the sintering temperature, since the melting point of cobalt is high, at a lower temperature, B cannot drive the penetration of cobalt element into the secondary particles, and when the temperature is too high, B and Co enter the crystal lattice, which changes the growth and development of the grain, causes lattice defects to a certain extent, and thus deteriorates the capacity and high-temperature cycle performance.

[0100] In Example 5, the coating element Al is increased, which has no obvious influence on the micro stress of the positive active material and the lithium-nickel mixing degree, but since the Al element reduces the contact between the positive active material and the electrolyte, it inhibits the side decomposition reaction, and the high-temperature cycle performance is improved to a certain extent.

[0101] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in the present specification and the features of the different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0102] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes a main body and a coating layer. The chemical formula of the main body includes: Li 1+a Ni x Mr y Co z M b O2, where, -0.05 ≤ a ≤ 0.1, 0 < b ≤ 0.05, 0 < x < 1, 0 < y < 1, 0 ≤ z ≤ 0.03, and M includes one or more of Zr, Y, W, Nb, Sr, Al, Mg, Mo, La, Er, and Si; The coating layer includes cobalt element and boron element. The thickness of the coating layer is 5 nm - 20 nm, and the penetration degree of the cobalt element into the main body is 0.4 - 0.

9.

2. The positive electrode active material according to claim 1, characterized in that, In the coating layer, the molar ratio of the boron element to the cobalt element is (2.7 - 5.5):1; and / or, The particle strength of the positive electrode active material is 120 MPa - 180 MPa.

3. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies at least one of the following conditions: M includes one or more of Zr, Y, and Al; x=0.50-0.95； y=0.05-0.50； The thickness of the coating layer is 5 nm - 10 nm; The penetration degree of the cobalt element into the main body is 0.6 - 0.

9.

4. The positive electrode active material according to claim 1, characterized in that, The coating layer further includes M1 element, and the M1 element includes one or more of Ti, Mg, Al, W, Zr, V, and Sr. Optionally, the molar ratio of the M1 element to the cobalt element in the coating layer is (0.0001 - 5. The positive electrode active material according to any one of claims 1-4, characterized in that, ​ ​ ​ 6. The positive electrode active material according to any one of claims 1-4, characterized in that, ​ ​ The specific surface area of ​​the positive electrode active material is 0.45 m². 2 / g-1.50m 2 / g, can be selected as 0.60m 2 / g-1.20m 2 / g; ​ 7. A method for preparing the positive electrode active material according to any one of claims 1-6, characterized in that, ​ ​ ​ 8. The method according to claim 7, characterized in that, ​ ​ ​ ​ ​ ​ ​ ​ 9. A positive electrode sheet, characterized in that, ​ 10. A battery, characterized in that, ​ 11. An electrical appliance, characterized in that, ​

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