Positive electrode materials and their preparation methods, secondary batteries and electrical devices

Abstract

This invention provides a cathode material, its preparation method, a secondary battery, and an electrical device. The cathode material includes a substrate, a first coating layer covering at least a portion of the surface of the substrate, and a second coating layer covering at least a portion of the surface of the first coating layer. The substrate material includes lithium nickel oxide, wherein nickel accounts for 83%-100% of the total molar percentage of elements other than lithium and oxygen in the lithium nickel oxide. The first coating layer material includes a lithium-containing solid solution. The second coating layer material includes boron. By coating the basic surface with a first coating layer, replacing the traditional water washing process, the side reaction between residual lithium and water in the cathode material can be reduced, the residual alkali content in the cathode material can be reduced, the amount of gas generated can be reduced, and the battery safety performance can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a cathode material and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] With the rapid development of new energy vehicles, the demand for high energy density in power batteries is increasing daily, making the improvement of energy density in lithium-ion power batteries a focus of society. In lithium-ion batteries, the cathode material is the main lithium-ion electrode material. + Developing high-specific-capacity cathode materials is key to achieving high energy density performance in electric vehicle batteries.

[0003] High-nickel cathode materials are considered candidate cathode materials for power batteries due to their advantages such as low cost, high specific capacity, and long cycle life. However, research has found that while the specific capacity of high-nickel cathode materials increases significantly with increasing nickel content, the safety performance of the battery deteriorates. Summary of the Invention

[0004] Therefore, it is necessary to provide a cathode material and its preparation method, a secondary battery, and an electrical device, so that the specific capacity of the material can be improved while the battery has high safety.

[0005] A first aspect of the present invention provides a cathode material comprising:

[0006] The matrix material comprises lithium nickel oxide, wherein the molar percentage of nickel in the total number of elements other than lithium and oxygen is 83%-100%;

[0007] A first coating layer is applied to at least a portion of the surface of the substrate. The material of the first coating layer comprises a lithium-containing solid solution with the chemical formula Li. a M″ n b O c The M″ element includes one or more of Co, Mn, Y, S, Ta, Ti, Zr, Nb, W, and P, where n is the valence state of the M″ element, and a + nb = 2c; and

[0008] A second coating layer is applied to at least a portion of the surface of the first coating layer, and the material of the second coating layer includes boron.

[0009] In some embodiments, the lithium nickel oxide has the chemical formula Li w Ni x M y M zO2, wherein the M element includes one or more of Co, Mn and Al, and the M′ element is a dopant element, including one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb and Sr, with 0.95≤w≤1.05, 0.83≤x≤1.0, 0≤z<0.1, and x+y+z=1.

[0010] In some embodiments, the material of the second coating layer includes one or more lithium borate compounds;

[0011] Optionally, the material of the second coating layer includes lithium borate.

[0012] In some embodiments, the cathode material has at least one of the following characteristics:

[0013] (1) The substrate material is a single-crystal primary particle; the average particle size of the substrate material is 2μm-5μm; the average particle size of the cathode material is 2.5μm-6μm;

[0014] (2) The matrix material is an agglomerate; the average particle size of the matrix material is 10 μm-12 μm; the average particle size of the cathode material is 10.5 μm-12.5 μm;

[0015] (3) The thickness of the first coating layer is 5nm-20nm;

[0016] (4) The thickness of the second coating layer is 2nm-5nm;

[0017] (5) The mass ratio of the first coating layer to the substrate is (1-15):100;

[0018] (6) The ratio of the mass of the second coating layer to the total mass of the substrate and the first coating layer is (0.02-0.5):1.

[0019] A second aspect of the present invention provides a method for preparing the cathode material of the first aspect of this application, comprising the following steps:

[0020] The matrix is ​​prepared by mixing a nickel-containing precursor and a lithium source and performing a first sintering treatment.

[0021] The matrix and the M″-containing compound are mixed and subjected to a second sintering treatment to prepare the first coating layer on at least a portion of the outer surface of the matrix, thereby obtaining an intermediate.

[0022] The intermediate is mixed with a boron source, water is sprayed in during the mixing process, and a third sintering treatment is performed to prepare a second coating layer on at least a portion of the outer surface of the first coating layer, thereby obtaining the positive electrode material.

[0023] In some embodiments, the first sintering process includes at least one of the following conditions:

[0024] (1) The chemical formula of the nickel-containing precursor is Ni d M 1-d (OH)2, wherein the element M includes one or more of Co, Mn and Al, and 0.9≤d≤1.0;

[0025] (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate and lithium oxalate;

[0026] (3) The molar ratio of lithium element in the lithium source to the nickel-containing precursor is (1.02-1.06):1;

[0027] (4) When performing the first sintering treatment, a compound containing doped element M′ is also added;

[0028] Optionally, the compound containing doped element M′ includes one or more of oxides, oxalates, carbonates, hydroxides, and organometallic compounds containing element M′, and the doped element M′ includes one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb, and Sr; further optionally, the compound containing doped element M′ includes oxides containing element M′.

[0029] Optionally, the mass ratio of the compound containing the doped element M′ to the nickel-containing precursor is (0.05-0.5):100;

[0030] (5) The first sintering temperature is 700℃-900℃, the sintering time is 10h-20h, and the heating rate is 2℃ / min-5℃ / min.

[0031] In some embodiments, the second sintering process includes at least one of the following conditions:

[0032] (1) The M″-containing compound includes one or more of oxides, oxalates, carbonates, hydroxides and organometallic compounds containing the M″ element;

[0033] (2) The mass ratio of the M″-containing compound to the matrix is ​​(0.5-5):100;

[0034] (3) The second sintering temperature is 600℃-800℃, the sintering time is 6h-12h, and the heating rate is 2℃ / min-5℃ / min.

[0035] In some embodiments, the third sintering process includes at least one of the following conditions:

[0036] (1) The boron source includes one or more of boron hydroxide and boron oxide;

[0037] (2) The mass ratio of the boron source to the intermediate is (0.05-0.3):100;

[0038] (3) The mass ratio of the water to the intermediate is (1-2):100;

[0039] (4) The temperature of the third sintering is 250℃-450℃, the sintering time is 6h-10h, and the heating rate is 1℃ / min-3℃ / min.

[0040] A third aspect of the present invention provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector;

[0041] Wherein, the positive electrode active material layer includes the positive electrode material of the first aspect of this application; or

[0042] The positive electrode active material layer includes a positive electrode material prepared using the preparation method as described in the second aspect of this application.

[0043] A fourth aspect of the present invention provides an electrical device comprising a secondary battery according to the third aspect of this application.

[0044] The aforementioned cathode material, its preparation method, secondary battery, and electrical device, wherein the cathode material includes a substrate, a first coating layer covering the surface of the substrate, and a second coating layer covering the surface of the first coating layer; on the one hand, by coating the surface of the substrate with the first and second coating layers, the present invention reduces the generation of alkaline compounds (such as Li2CO3 and LiOH) on the surface of the cathode material, thereby reducing the amount of residual alkali on the surface of the cathode material, thereby reducing the amount of gas generated due to the side reaction between residual alkali and electrolyte, and improving battery safety performance; on the other hand, the present invention develops a process to replace traditional water washing to reduce the surface residual alkali content, which can reduce the proton exchange reaction between residual lithium and water on the surface of the cathode material during water washing, stabilize the surface structure of the cathode material, and improve the electrochemical capacity and cycle performance of the material. Attached Figure Description

[0045] Figure 1 This is a scanning electron microscope image of the positive electrode material prepared in Example 1;

[0046] Figure 2 This is a scanning electron microscope image of the positive electrode material prepared in Example 5;

[0047] Figure 3 The image shows a scanning electron microscope (SEM) image of the cathode material prepared in Comparative Example 1.

[0048] Figure 4 This is a schematic diagram of the first charge-discharge test results for Example 1 and Comparative Examples 1-4;

[0049] Figure 5 This is a schematic diagram of the cyclic test results for Example 1 and Comparative Examples 1-4. Detailed Implementation

[0050] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0052] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0053] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0054] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0055] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument.

[0056] In the description of the invention, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form new technical solutions.

[0058] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially.

[0059] High-nickel cathode materials are considered promising candidates for power batteries due to their advantages such as low cost, high specific capacity, and long cycle life. However, while increasing the nickel content in high-nickel cathode materials significantly improves specific capacity, it also degrades battery safety. Researchers have discovered that with increasing nickel content, especially when it exceeds 80%, the presence of residual lithium on the surface of the high-nickel cathode material makes it more sensitive to H2O and CO2 in the air. This leads to the formation of alkaline compounds (such as Li2CO3 and LiOH) on the material surface, increasing the amount of residual alkali. This residual alkali readily reacts with the electrolyte at high temperatures to generate gas, causing battery swelling and consequently reducing battery safety. Furthermore, the increased residual alkali on the material surface also leads to water absorption during the homogenization process in battery manufacturing, resulting in poor processing performance.

[0060] The first aspect of this application provides a cathode material, comprising a substrate, a first coating layer covering at least a portion of the surface of the substrate, and a second coating layer covering at least a portion of the surface of the first coating layer; the substrate material comprises lithium nickel oxide, wherein the molar percentage of nickel in the total number of elements other than lithium and oxygen is 83%-100% in the lithium nickel oxide; the first coating layer material comprises a lithium-containing solid solution, the chemical formula of which is Li a M″ n b O c The M″ element includes one or more of Co, Mn, Y, S, Ta, Ti, Zr, Nb, W and P, where n is the valence state of the M″ element, and a + nb = 2c; the material of the second coating layer includes boron.

[0061] It should be noted that the matrix material can be either single-crystal primary particles or aggregates. Aggregates refer to collections formed by single-crystal primary particles connected to each other at edges or corners.

[0062] Lithium nickel oxide refers to oxides containing lithium and nickel elements. Lithium nickel oxide may or may not be doped with other metal elements, depending on the requirements.

[0063] The first coating layer may cover the entire surface of the substrate, or it may cover only a portion of the surface of the substrate; preferably, the first coating layer covers the entire surface of the substrate. The second coating layer may cover the entire surface of the first coating layer, or it may cover only a portion of the surface of the first coating layer; preferably, the second coating layer covers the entire surface of the first coating layer. Of course, it is understood that if the first coating layer does not cover the entire surface of the substrate, the second coating layer may also be directly coated on the surface of the substrate.

[0064] The matrix can be entirely composed of lithium nickel oxide, or it can be a mixture of lithium nickel oxide and other substances that can be used as cathode materials. The first coating layer can be entirely composed of lithium-containing solid solution, or it can be a mixture of lithium-containing solid solution and other substances; preferably, the first coating layer is entirely composed of lithium-containing solid solution.

[0065] The molar percentage of nickel in the total amount of elements other than lithium and oxygen refers to the proportion of the molar amount of nickel in lithium nickel oxide to the total molar amount of all elements excluding lithium and oxygen.

[0066] Understandably, the aforementioned cathode material includes a substrate, a first coating layer covering the surface of the substrate, and a second coating layer covering the surface of the first coating layer. In a first aspect, by coating the surface of the substrate with the first and second coating layers, the present invention reduces the formation of alkaline compounds (e.g., Li₂CO₃ and LiOH) on the surface of the cathode material, thereby reducing the amount of residual alkali on the surface of the cathode material. This reduces the amount of gas generated due to side reactions between the residual alkali and the electrolyte, improving battery safety performance. In another aspect, the present invention develops a process to replace traditional water washing for reducing surface residual alkali content. This process reduces the proton exchange reaction between residual lithium and water in the cathode material during water washing, stabilizes the surface structure of the cathode material, and improves the electrochemical capacity and cycle performance of the material. Simultaneously, because the amount of residual alkali in the cathode material is reduced, water absorption during the preparation of the cathode slurry can be reduced or avoided, optimizing processing performance.

[0067] The M″ element added during the preparation of the first coating layer can consume lithium on the substrate surface at high temperatures, generating a lithium-containing solid solution with good conductivity, Li. a M″ n b O cCoating the substrate surface and modifying the surface allows the first coating layer to adhere more tightly to the substrate, promoting lithium ion insertion / extraction during charging and discharging. The addition of deionized water during the preparation of the second coating layer increases the wettability of the particle surface, allowing boron to better penetrate the surface of the first coating layer during sintering, forming lithium borate compounds. This reduces the specific surface area of ​​the cathode material, suppresses the overflow of transition metal ions, and results in higher structural and thermal stability of the cathode material.

[0068] Furthermore, by coating the surface of the substrate with a first coating layer instead of the traditional water washing process, the resulting cathode material has stronger stability, thereby improving battery capacity and cycle performance.

[0069] In some embodiments, the chemical formula of lithium nickel oxide is Li w Ni x M y M z The oxide matrix M' is a dopant element, comprising one or more of Co, Mn, and Al, and one or more of Al, Mo, Y, Ta, Nb, Sb, and Sr, with the following properties: 0.95 ≤ w ≤ 1.05, 0.83 ≤ x ≤ 1.0, 0 ≤ z < 0.1, and x + y + z = 1. Doping lithium nickel oxide with M' stabilizes the crystal structure of the matrix, suppresses phase transitions, and improves the stability of the cathode material.

[0070] As one possible implementation, the material of the second coating layer includes one or more lithium borate compounds; when preparing the second coating layer, the boron element in the boron source reacts with the lithium element remaining on the surface of the first coating layer to form a lithium borate compound as the second coating layer, and the boron element can better melt and penetrate into the surface of the first coating layer, thereby reducing the specific surface area of ​​the cathode material.

[0071] It should be noted that lithium borate compounds refer to a series of compounds formed by lithium borate doped with other elements and without other elements.

[0072] Optionally, the material of the second coating layer includes lithium borate.

[0073] In some possible implementations, the substrate material is a single crystal. When the substrate material is a single crystal, the battery produces relatively less gas after fabrication, resulting in higher safety. The average particle size of the substrate material is 2μm-5μm; for example, it can be, but is not limited to, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or any two of the above values. When the average particle size of the single-crystal substrate material is within the above range, the kinetics of the cathode material are relatively good, resulting in excellent capacity and rate performance; when the average particle size of the substrate material is higher than the above range, the lithium-ion diffusion path increases, affecting lithium-ion transport; when the average particle size of the substrate material is lower than the above range, the cathode material fabrication process becomes more difficult. The average particle size of the cathode material is 2.5μm-6μm; for example, it can be, but is not limited to, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, or any two of the above values.

[0074] In some possible implementations, the matrix material is an agglomerate; when the matrix material is an agglomerate, the cathode material can have a higher compaction density and capacity. The average particle size of the matrix material is 10 μm-12 μm; for example, it can be, but is not limited to, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any two of the above values. When the average particle size of the agglomerate matrix material is within the above range, the cathode material particles have better strength; when the average particle size of the matrix material is below the above range, the compaction density of the cathode material may decrease; when the average particle size of the matrix material is above the above range, the cathode material particles are prone to cracking. The average particle size of the cathode material is 10.5 μm-12.5 μm; for example, it can be, but is not limited to, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, or any two of the above values.

[0075] In some embodiments, the thickness of the first coating layer is 5nm-20nm; for example, it can be, but is not limited to, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, or any two of the above values. When the thickness of the first coating layer is within the above range, the residual alkali content on the surface of the cathode material particles can be reduced, and the formed lithium-containing solid solution can promote the intercalation and deintercalation of lithium ions during charging and discharging, thereby improving the electrochemical performance of the cathode material; when the thickness of the first coating layer is greater than the above range, it may affect the intercalation and deintercalation of lithium ions during charging and discharging.

[0076] In some embodiments, the thickness of the second coating layer is 2nm-5nm; for example, it can be, but is not limited to, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, or any two of the above values. When the thickness of the second coating layer is within the above range, the specific surface area of ​​the cathode material can be reduced, the overflow of transition metal ions can be suppressed, and the cathode material can have higher structural stability and thermal stability.

[0077] In some embodiments, the mass ratio of the first coating layer to the substrate is (1-15):100; for example, it can be, but is not limited to, 1:100, 2:100, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100, 15:100, or any two of the above ratios. When the mass ratio of the first coating layer to the substrate is within the above range, the residual alkali content on the surface of the cathode material particles can be reduced, the subsequent cathode material electrode processing technology can be optimized, and the electrochemical performance of the cathode material can be improved.

[0078] In some embodiments, the mass ratio of the second coating layer to the total mass of the substrate and the first coating layer is (0.02-0.5):100; for example, it can be, but is not limited to, 0.02:100, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, 0.35:100, 0.4:100, 0.45:100, 0.5:100, or any range between two of the above ratios. When the mass ratio of the second coating layer to the total mass of the substrate and the first coating layer is within the above range, the structural stability and thermal stability of the cathode material can be improved, and the electrochemical performance of the cathode material can be enhanced.

[0079] A second aspect of the present invention provides a method for preparing the cathode material of the first aspect, comprising the following steps:

[0080] A nickel-containing precursor and a lithium source are mixed and subjected to a first sintering treatment to prepare a matrix;

[0081] The matrix and the M″-containing compound are mixed and subjected to a second sintering treatment to prepare a first coating layer on at least a portion of the outer surface of the matrix, thereby obtaining an intermediate.

[0082] The intermediate is mixed with a boron source, water is sprayed in during the mixing process, and a third sintering treatment is performed to prepare a second coating layer on at least a portion of the outer surface of the first coating layer, thereby obtaining the cathode material.

[0083] The nickel-containing precursor can be a single crystal or an agglomerate; when the nickel-containing precursor is a single crystal, the material of the resulting matrix is ​​a single crystal; when the nickel-containing precursor is an agglomerate, the material of the resulting matrix is ​​an agglomerate.

[0084] Adding water during the preparation of the second coating layer can increase the wettability of the intermediate surface, allowing boron to melt and penetrate better into the surface of the first coating layer during sintering. This reduces the specific surface area of ​​the resulting cathode material, suppresses the overflow of transition metal ions, and gives the cathode material better structural and thermal stability.

[0085] When preparing cathode materials, by coating the outer surface of the substrate with a first coating layer instead of the traditional water washing process, the side reaction between residual lithium and water in the cathode material can be reduced, the generation of alkaline compounds in the cathode material can be reduced, and the amount of residual alkali in the cathode material can be reduced. This can reduce the amount of gas generated due to the side reaction between residual alkali and electrolyte, and improve the battery safety performance.

[0086] In some embodiments, the chemical formula of the nickel-containing precursor is Ni d M 1-d (OH)2, wherein the M element includes one or more of Co, Mn and Al, and 0.9≤d≤1.0.

[0087] As one possible implementation, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate, and lithium oxalate.

[0088] In some possible implementations, the molar ratio of lithium in the lithium source to the nickel-containing precursor is (1.02-1.06):1; for example, it can be, but is not limited to, 1.02:1, 1.025:1, 1.03:1, 1.035:1, 1.04:1, 1.045:1, 1.05:1, 1.055:1, 1.06:1, or any two of the above ratios. When the molar ratio of lithium in the lithium source to the nickel-containing precursor is within the above range, the matrix particles exhibit better crystallinity, and the prepared cathode material exhibits excellent electrochemical performance.

[0089] In some embodiments, a compound containing doped element M′ is added during the first sintering process; optionally, the compound containing doped element M′ includes one or more of oxides, oxalates, carbonates, hydroxides, and organometallic compounds containing element M′, and the doped element M′ includes one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb, and Sr; further optionally, the compound containing doped element M′ includes oxides containing element M′.

[0090] Optionally, the mass ratio of the compound containing dopant element M′ to the nickel-containing precursor is (0.05-0.5):100; for example, it can be, but is not limited to, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, 0.35:100, 0.4:100, 0.45:100, 0.5:100, or any range between two of the above ratios. When the mass ratio of the M′-containing compound to the nickel-containing precursor is within the above range, it can suppress the structural phase transition of the matrix and improve the structural stability of the matrix. The dopant element M′ includes one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb, and Sr.

[0091] In some embodiments, the sintering temperature of the first sintering treatment is 700℃-900℃; for example, it can be, but is not limited to, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, or any range between any two of the above values. The sintering time of the first sintering treatment is 10h-20h; for example, it can be, but is not limited to, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or any range between any two of the above values. The heating rate for the first sintering treatment is 2℃ / min to 5℃ / min; for example, it can be, but is not limited to, 2℃ / min, 2.3℃ / min, 2.5℃ / min, 2.7℃ / min, 3℃ / min, 3.3℃ / min, 3.5℃ / min, 3.8℃ / min, 4℃ / min, 4.3℃ / min, 4.5℃ / min, 4.8℃ / min, 5℃ / min, or any range between two of the above values.

[0092] It should be noted that the heating rate of the first sintering treatment refers to the rate at which the nickel-containing precursor, lithium source, and M′-containing compound rise from their own temperature at the start of the first sintering treatment to the sintering temperature.

[0093] In some embodiments, the M″-containing compound includes one or more of oxides, oxalates, carbonates, hydroxides, and organometallic compounds containing the M″ element.

[0094] In some embodiments, the mass ratio of the M″-containing compound to the matrix is ​​(0.5-5):100; for example, it can be, but is not limited to, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, or any two of the above ratios. When the mass ratio of the matrix to the M″-containing compound is within the above range, the residual alkali content on the matrix surface can be significantly reduced, thereby improving the stability of the cathode material and enhancing its electrochemical performance.

[0095] In some embodiments, the sintering temperature of the second sintering treatment is 600℃-800℃; for example, it can be, but is not limited to, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, or any range between any two of the above values. The sintering time of the second sintering treatment is 6h-12h; for example, it can be, but is not limited to, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or any range between any two of the above values. The heating rate for the second sintering treatment is 2℃ / min to 5℃ / min; for example, it can be, but is not limited to, 2℃ / min, 2.3℃ / min, 2.5℃ / min, 2.7℃ / min, 3℃ / min, 3.3℃ / min, 3.5℃ / min, 3.8℃ / min, 4℃ / min, 4.3℃ / min, 4.5℃ / min, 4.8℃ / min, 5℃ / min, or any range between two of the above values.

[0096] It should be noted that the heating rate of the second sintering treatment refers to the rate at which the matrix and the M″-containing compound rise from their own temperature at the start of the second sintering treatment to the sintering temperature.

[0097] As one possible implementation, the boron source includes one or more of boron hydroxide and boron oxide.

[0098] In some embodiments, the mass ratio of boron source to intermediate is (0.05-0.3):100; for example, it can be, but is not limited to, 0.05:100, 0.1:100, 0.15:100, 0.2:100, 0.25:100, 0.3:100, or any two of the above ratios. When the mass ratio of boron source to intermediate is within the above range, the structural stability of the cathode material can be improved, and its electrochemical performance can be enhanced.

[0099] In some possible implementations, the mass ratio of water to the intermediate is (1-2):100; for example, it can be, but is not limited to, 1:100, 1.1:100, 1.2:100, 1.3:100, 1.4:100, 1.5:100, 1.6:100, 1.7:100, 1.8:100, 1.9:100, 2:100, or any range between two of the above ratios. When the mass ratio of water to the intermediate is within the above range, the intermediate particles can have better wettability, thus better utilizing the role of boron; it is understood that the water can be deionized water, pure water, ultrapure water, etc.

[0100] In some embodiments, the sintering temperature of the third sintering treatment is 250℃-450℃; for example, it can be, but is not limited to, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, or any range between two of the above values. The sintering time of the third sintering treatment is 6h-10h; for example, it can be, but is not limited to, 6h, 7h, 8h, 9h, 10h, or any range between two of the above values. The heating rate for the third sintering process is 1℃ / min to 3℃ / min; for example, it can be, but is not limited to, 1℃ / min, 1.1℃ / min, 1.2℃ / min, 1.3℃ / min, 1.4℃ / min, 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min, 2℃ / min, 2.1℃ / min, 2.2℃ / min, 2.3℃ / min, 2.4℃ / min, 2.5℃ / min, 2.6℃ / min, 2.7℃ / min, 2.8℃ / min, 2.9℃ / min, 3℃ / min, or any range between two of the above values.

[0101] It should be noted that the heating rate of the third sintering process refers to the rate at which the intermediate and the boron source rise from their own temperature at the start of the third sintering process to the sintering temperature.

[0102] In some embodiments, the method for preparing the cathode material of the first aspect of the present invention includes the following steps:

[0103] A nickel-containing precursor, a lithium source, and a compound containing doped element M′ were mixed and subjected to a first sintering treatment at 700℃-900℃ for 10-20 hours at a heating rate of 2℃ / min-5℃ / min. The nickel-containing precursor has the chemical formula Ni. d M 1-d(OH)2, wherein element M includes one or more of Co, Mn and Al, 0.9≤d≤1.0; lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate and lithium oxalate; compound containing dopant element M′ includes one or more of oxides, oxalates, carbonates, hydroxides and organometallic compounds containing element M′; the molar ratio of lithium element in the lithium source to nickel-containing precursor is (1.02-1.06):1; the mass ratio of compound containing dopant element M′ to nickel-containing precursor is (0-0.5):100, optionally (0.05-0.5):100; element M′ includes one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb and Sr;

[0104] The matrix and the M″-containing compound are mixed uniformly, and a second sintering treatment is carried out at 600℃-800℃ for 6-12 hours with a heating rate of 2℃ / min-5℃ / min. A first coating layer is prepared on at least a portion of the surface of the matrix to obtain an intermediate. The M″-containing compound includes one or more of oxides, oxalates, carbonates, hydroxides, and organometallic compounds containing the M″ element. The M″ element includes one or more of Co, Mn, Y, S, Ta, Ti, Zr, Nb, W, and P. The mass ratio of the M″-containing compound to the matrix is ​​(0.5-5):100.

[0105] The intermediate is mixed with a boron source, water is sprayed in during the mixing process, and the mixture is homogeneous. A third sintering treatment is carried out at 250℃-450℃ for 6-10 hours with a heating rate of 1℃ / min-3℃ / min. A second coating layer is prepared on at least a portion of the surface of the first coating layer to obtain the cathode material. The boron source includes one or more of boron hydroxide and boron oxide. The mass ratio of boron source to intermediate is (0.05-0.3):100. The mass ratio of water to intermediate is (1-2):100.

[0106] A third aspect of the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer located on at least one side of the positive current collector; wherein the positive active material layer comprises the positive electrode material of the first aspect of the present invention; or the positive active material layer comprises a positive electrode material prepared using the preparation method of the second aspect of the present invention. The positive electrode sheet comprising the positive electrode material of the present invention has a high energy density.

[0107] A third aspect of the present invention provides a secondary battery comprising a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector; wherein the positive active material layer comprises the positive electrode material of the first aspect of the present invention; or the positive active material layer comprises a positive electrode material prepared using the preparation method of the second aspect of the present invention. The positive electrode sheet comprising the positive electrode material of the present invention has a high energy density, and the secondary battery exhibits improved capacity while possessing excellent safety and cycle performance.

[0108] A fourth aspect of the present invention provides an electrical device comprising a secondary battery according to a third aspect of the present invention.

[0109] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0110] I. Preparation of cathode materials

[0111] Example 1

[0112] Weigh Ni 0.93 Co 0.05 Mn 0.02 (OH)2 (as a nickel-containing precursor), LiOH (as a lithium source), Al2O3, and SrO (as a compound containing doped element M′) were mixed evenly, placed in an oxygen atmosphere, and sintered at 800℃ for 12 hours. After crushing, the matrix LiNi was obtained. 0.925 Co 0.05 Mn 0.019 Al 0.005 Sr 0.001 O2; wherein the molar ratio of lithium element in the lithium source to nickel-containing precursor is 1.035:1, the mass ratio of SrO to nickel-containing precursor is 0.1:100, and the mass percentage of Al2O3 to nickel-containing precursor is 0.3%;

[0113] The matrix and Co(OH)2 (as the M″-containing compound) were mixed evenly, and then the mixture was placed in a box furnace and sintered at 700°C for 8 hours. The first coating layer was coated on the outer surface of the matrix, and the intermediate was obtained after crushing. The thickness of the first coating layer was 10-12 nm, the mass ratio of the M″-containing compound to the matrix was 2.5:100, and the mass ratio of the first coating layer to the matrix was 2.67:100.

[0114] The intermediate was mixed with H3BO3 (as a boron source), and deionized water was sprayed in during the mixing process. After the mixture was evenly mixed, it was placed in a box furnace and sintered at 300°C for 8 hours. A second coating layer was then coated on the outer surface of the first coating layer. After sintering, the material was passed through a 325-mesh sieve to obtain the cathode material, which had an average particle size of 3 μm.

[0115] Example 2-10

[0116] The preparation methods of the cathode materials in Examples 2-10 are basically similar to those in Example 1, except that at least one of the following is different: the type of lithium source, the type and / or amount of nickel-containing precursor, the type and / or amount of M′-containing compound, the temperature and / or time of the first sintering treatment, the type and / or amount of M″-containing compound, the temperature and / or time of the second sintering treatment, the type and / or amount of boron source, the amount of deionized water, the temperature and time of the third sintering treatment, and the type and / or average particle size of the matrix.

[0117] The process parameters in Examples 2-10 are detailed in Table 1; the product parameters of the cathode materials obtained in Examples 2-10 are detailed in Table 2.

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1 is that only the substrate was prepared, and no coating layer was prepared on the substrate. See Table 1 for details.

[0120] Comparative Example 2

[0121] The difference between Comparative Example 2 and Example 1 is that no first coating layer was prepared, and only a water washing process was used to remove residual lithium from the outer surface of the substrate; all other aspects were the same. The specific process of the water washing is as follows:

[0122] Weigh the matrix and place it in deionized water, with a mass ratio of matrix to deionized water of 7:3. Stir at 180 rpm for 3 min, then filter and dry at 150℃ for 4 h; see Table 1 for details.

[0123] Comparative Example 3

[0124] The difference between Comparative Example 3 and Example 1 is that no second coating layer was prepared; all other aspects are the same, as detailed in Table 1.

[0125] Comparative Example 4

[0126] The difference between Comparative Example 4 and Example 1 is that deionized water was not sprayed in when preparing the second coating layer. All other aspects are the same, as detailed in Table 1.

[0127] Comparative Example 5

[0128] The difference between Comparative Example 5 and Example 5 is that only the substrate was prepared, and no coating layer was prepared on the substrate. See Table 1 for details.

[0129] Table 1. Process Parameters

[0130]

[0131] In Table 1, n1 represents the molar ratio of lithium in the lithium source to the nickel-containing precursor; n2 represents the mass ratio of compound 1 containing doped element M′ to the nickel-containing precursor; n3 represents the mass ratio of compound 2 containing doped element M′ to the nickel-containing precursor; T1 represents the first sintering temperature; t1 represents the first sintering time; n4 represents the mass ratio of compound containing M″ to the matrix; T2 represents the second sintering temperature; t2 represents the second sintering time; n5 represents the mass ratio of boron source to intermediate; n6 represents the mass ratio of deionized water to intermediate; T3 represents the third sintering temperature; and t3 represents the third sintering time.

[0132] Table 2

[0133]

[0134]

[0135] Where D1 represents the average particle size of the substrate, D2 represents the thickness of the first coating layer, D3 represents the thickness of the second coating layer, D4 represents the average particle size of the cathode material; n7 represents the mass ratio of the first coating layer to the substrate, and n8 represents the mass ratio of the second coating layer to the total mass of the substrate and the first coating layer.

[0136] The cathode materials prepared in Examples 1, 5, and Comparative Example 1 were scanned using an electron scanning electron microscope (SEM), and the results are shown below. Figure 1 , Figure 2 , Figure 3 As shown.

[0137] Depend on Figure 1 It can be seen that the cathode material prepared in Example 1 has a coating layer on its surface and the substrate used is a single crystal.

[0138] Depend on Figure 2 It can be seen that the positive electrode material prepared in Example 5 has a dense and uniform coating layer on its surface, and the matrix used is an agglomerate.

[0139] Depend on Figure 3 It can be seen that the surface of the material prepared in Comparative Example 1 is smooth, indicating that the surface of the matrix in Comparative Example 1 is uncoated.

[0140] II. Cathode Material Performance Testing

[0141] Weigh 5.000±0.050 g of positive electrode material powder and place it in 45 g of deionized water. Stir thoroughly for 10 min and filter using filter paper to obtain a clear aqueous solution containing dissolved LiOH and Li2CO3. Use 0.1 M HCl as the titrant and titrate using a potentiometric titrator. Determine the amount of HCl consumed based on the indicator or potential change and record the corresponding volume. Calculate the content of LiOH and Li2CO3 based on the volume of HCl consumed. The results are shown in Table 3.

[0142] Table 3

[0143] w(LiOH) / % <![CDATA[w(Li2CO3) / %]]> <![CDATA[w(Li + ) / %]]> Example 1 0.5024 0.3397 0.2108 Example 2 0.4987 0.3635 0.2142 Example 3 0.5200 0.3500 0.2179 Example 5 0.3731 0.2981 0.1640 Comparative Example 1 0.7052 0.6426 0.3252 Comparative Example 2 0.5256 0.3840 0.2259 Comparative Example 5 0.6000 0.6647 0.2988

[0144] Comparison of the results of Examples 1-3 and Comparative Example 1, and comparison of Example 5 and Comparative Example 5, shows that compared with the uncoated material, the content of residual LiOH and Li2CO3 on the surface of the coated cathode material of the present invention is significantly reduced. Comparison of the results of Examples 1-3 and Comparative Example 2 shows that compared with the amount of residual LiOH and Li2CO3 on the surface of the cathode material obtained by conventional water washing process, the amount of residual LiOH and Li2CO3 on the surface of the coated cathode material of the present invention is reduced, indicating that the coating process of the present invention can significantly reduce the residual alkali content on the surface of the cathode material.

[0145] III. Battery fabrication and performance testing

[0146] The cathode materials obtained in Examples 1-5, Examples 8-10, and Comparative Examples 1-5 were used to prepare coin cells. The specific preparation methods are as follows:

[0147] The positive electrode material, conductive agent SP, and binder PVDF were weighed at a mass ratio of 90:5:5 and added to an NMP solution. The mixture was stirred for 4 hours under argon protection to obtain a high-nickel positive electrode slurry required for the coin cell. This slurry was coated onto a smooth copper foil, dried, and then cut to form a positive electrode sheet. The positive electrode sheet, lithium metal sheet (negative electrode), separator, and electrolyte were then assembled to form a propylene carbonate coin cell. The separator was a 14 μm thick polypropylene membrane; the electrolyte contained LiPF6 at a concentration of 1 M.

[0148] The coin cells prepared above were subjected to their first charge-discharge test. The specific process was as follows: For single crystals, the test procedure was as follows: constant current charging at 0.1C to 4.30V, constant voltage charging to 50uA, and then discharge at 0.1C to 2.8V, completing one charge-discharge cycle. For aggregates, the test procedure was as follows: constant current charging at 0.1C to 4.25V at room temperature, constant voltage charging to 50uA, and then discharge at 0.1C to 2.5V, completing one charge-discharge cycle. The results are shown in Table 4.

[0149] The coin cells prepared above were subjected to cycle testing. Specifically, they were charged and discharged at 45°C for 50 cycles at a charge-discharge rate of 0.5C, and then the cycle capacity retention was tested. The results are shown in Table 4.

[0150] The initial charge-discharge test results of the coin cells in Example 1 and Comparative Examples 1-4 are as follows: Figure 4 As shown, the cycle test results of the coin cells in Example 1 and Comparative Examples 1-4 are as follows: Figure 5 As shown.

[0151] Table 4

[0152]

[0153]

[0154] The results above show that the cathode material prepared by the coating process of the present invention has higher first-cycle charge-discharge efficiency and cycle capacity retention, indicating that the cathode material of the present invention has higher capacity and better cycle performance.

[0155] The difference between Examples 1-3 and Comparative Example 1 is that two layers of coating were performed; the difference between Examples 1-3 and Comparative Example 2 is that a double-layer coating was performed outside the substrate, without using the traditional water washing process; the difference between Example 1 and Comparative Example 3 is that a double-layer coating was performed in Example 1, while only a single-layer coating was performed in Comparative Example 3; the difference between Example 5 and Comparative Example 5 is that a double-layer coating was performed. A comparison of the results of the above examples and comparative examples shows that compared with no coating on the substrate surface, only a single-layer coating, or using the traditional water washing process to replace the first coating layer, the cathode material prepared by the coating process of the present invention has higher first-cycle charge-discharge efficiency and cycle capacity retention, indicating that the cathode material of the present invention has higher capacity and better cycle performance.

[0156] The difference between Examples 1, 8-10, and Comparative Example 4 lies in the amount of deionized water added during the preparation of the second coating layer. Comparison of the results from each set of examples and comparative examples shows that adding deionized water during the preparation of the second coating layer, with the amount of deionized water within 1-2 wt%, can improve the cycle capacity retention and first-cycle charge-discharge efficiency of the secondary battery. However, when the amount of deionized water added is greater than 2 wt%, both the first-cycle charge-discharge efficiency and cycle capacity retention of the secondary battery decrease. Technicians analyzed that this may be due to excessive moisture on the surface of the intermediate particles, increased material viscosity, poor mixing uniformity, and impact on subsequent lithium-ion intercalation / deintercalation, leading to a deterioration in the electrochemical performance of the secondary battery. Therefore, when the ratio of the amount of deionized water added to the total mass of the substrate and the first coating layer is (1-2):100 during the preparation of the second coating layer, it helps to improve the structural stability and thermal stability of the cathode material, thereby improving the cycle performance of the secondary battery.

[0157] The first-cycle charge-discharge efficiency and cycle capacity retention of Example 5 are lower than those of other examples, mainly because the charge-discharge voltage of the agglomerate electrical performance test is lower than that of the single crystal.

[0158] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0159] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A positive electrode material, characterized in that, include: The matrix material comprises lithium nickel oxide, wherein the molar percentage of nickel in the total amount of elements other than lithium and oxygen is 83%-100%; A first coating layer is applied to at least a portion of the surface of the substrate. The material of the first coating layer comprises a lithium-containing solid solution with the chemical formula Li. a M″ n b O c The M″ element includes one or more of Co, Mn, Y, S, Ta, Ti, Zr, Nb, W and P, where n is the valence state of the M″ element, and a + nb = 2c. as well as A second coating layer is applied to at least a portion of the surface of the first coating layer, and the material of the second coating layer includes boron. The method for preparing the cathode material includes the following steps: The matrix is ​​prepared by mixing a nickel-containing precursor and a lithium source and performing a first sintering treatment. The matrix and the M″-containing compound are mixed and subjected to a second sintering treatment to prepare the first coating layer on at least a portion of the outer surface of the matrix, thereby obtaining an intermediate. The intermediate is mixed with a boron source, water is sprayed in during the mixing process, and a third sintering treatment is performed to prepare a second coating layer on at least a portion of the outer surface of the first coating layer, thereby obtaining the positive electrode material.

2. The cathode material as described in claim 1, characterized in that, The chemical formula of the lithium nickel oxide is Li w Ni x M y M z O2, wherein the M element includes one or more of Co, Mn and Al, and the M′ element is a dopant element, including one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb and Sr, with 0.95≤w≤1.05, 0.83≤x≤1.0, 0≤z<0.1, and x+y+z=1.

3. The positive electrode material as described in claim 1, characterized in that, The material of the second coating layer includes one or more lithium borate compounds.

4. The cathode material as described in claim 3, characterized in that, The material of the second coating layer includes lithium borate.

5. The positive electrode material as described in claim 1, characterized in that, The cathode material has at least one of the following characteristics: (1) The substrate material is a single-crystal primary particle; the average particle size of the substrate material is 2μm-5μm; the average particle size of the cathode material is 2.5μm-6μm; (2) The matrix material is an agglomerate; the average particle size of the matrix material is 10 μm-12 μm; the average particle size of the cathode material is 10.5 μm-12.5 μm; (3) The thickness of the first coating layer is 5nm-20nm; (4) The thickness of the second coating layer is 2nm-5nm; (5) The mass ratio of the first coating layer to the substrate is (1-15):100; (6) The ratio of the mass of the second coating layer to the total mass of the substrate and the first coating layer is (0.02-0.5):

100.

6. The positive electrode material as described in claim 1, characterized in that, The first sintering process includes at least one of the following conditions: (1) The chemical formula of the nickel-containing precursor is Ni d M 1-d (OH)2, wherein the element M includes one or more of Co, Mn and Al, and 0.9≤d≤1.0; (2) The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate and lithium oxalate; (3) The molar ratio of lithium element in the lithium source to the nickel-containing precursor is (1.02-1.06):1; (4) When performing the first sintering treatment, a compound containing doped element M′ is also added; (5) The temperature of the first sintering is 700℃-900℃, the sintering time is 10h-20h, and the heating rate is 2℃ / min-5℃ / min.

7. The cathode material as described in claim 6, characterized in that, The compound containing the doped element M′ includes one or more of oxides, oxalates, carbonates, hydroxides, and organometallic compounds containing the element M′, and the doped element M′ includes one or more of Al, Ti, Zr, Mg, W, Mo, Y, Ta, Nb, Sb, and Sr.

8. The cathode material as described in claim 7, characterized in that, The compound containing the doped element M′ includes oxides containing the element M′.

9. The cathode material as described in claim 6, characterized in that, The mass ratio of the compound containing doped element M′ to the nickel-containing precursor is (0.05-0.5):

100.

10. The cathode material as described in claim 1, characterized in that, The second sintering process includes at least one of the following conditions: (1) The M″-containing compound includes one or more of oxides, oxalates, carbonates, hydroxides and organometallic compounds containing the M″ element; (2) The mass ratio of the M″-containing compound to the matrix is ​​(0.5-5):100; (3) The second sintering temperature is 600℃-800℃, the sintering time is 6h-12h, and the heating rate is 2℃ / min-5℃ / min.

11. The cathode material according to any one of claims 1 to 10, characterized in that, The third sintering process includes at least one of the following conditions: (1) The boron source includes one or more of boron hydroxide and boron oxide; (2) The mass ratio of the boron source to the intermediate is (0.05-0.3):100; (3) The mass ratio of the water to the intermediate is (1-2):100; (4) The temperature of the third sintering is 250℃-450℃, the sintering time is 6h-10h, and the heating rate is 1℃ / min-3℃ / min.

12. A secondary battery, characterized in that, It includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector; The positive electrode active material layer includes the positive electrode material as described in any one of claims 1 to 11.

13. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 12.

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