Positive electrode material, method for preparing the same, positive electrode sheet, and battery

Abstract

The present application provides a cathode material, a preparation method thereof, a cathode sheet and a battery, relating to the technical field of cathode materials. The preparation method includes the following steps: coating a lithium compound, a divalent cobalt compound, a trivalent cobalt compound and an optional M compound on the surface of spherical nickel hydroxide, and then performing a first sintering on the coated material under aerobic conditions; wherein, the molar content of the trivalent cobalt compound in the cobalt compounds is 50%-85%. This preparation method adopts the scheme of co-coating spherical nickel hydroxide with a divalent cobalt compound and a trivalent cobalt compound and then sintering, which can not only form a uniform lithium cobaltate coating layer on the surface of lithium nickelate particles, but also form cobalt doping inside the lithium nickelate particles. While ensuring a high nickel content of the material, it can effectively inhibit the phase change of the material and the side reaction with the electrolyte, and significantly improve the rate performance, cycle stability and capacity advantage of the material.

Description

Technical Field

[0001] The present application relates to the technical field of cathode materials, and particularly to a cathode material, a preparation method thereof, a cathode sheet and a battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in many fields such as automobiles and mobile devices due to their high voltage, high energy density and long life, and the cathode material directly determines the main performance of lithium-ion batteries. With the increasing market demand for battery energy density, high-nickel materials have become one of the most promising cathode materials for lithium-ion batteries.

[0003] However, high-nickel materials often have the disadvantages of poor cycling performance and low safety. Therefore, developing a high-nickel cathode material with long cycle life and high safety has become an urgent task for those skilled in the art. Summary of the Invention

[0004] Based on this, it is necessary to provide a cathode material with good cycling performance and high safety performance, a preparation method thereof and an application.

[0005] In the first aspect of the present application, a cathode material is provided, including lithium nickel composite oxide particles, the outer surface of the lithium nickel composite oxide particles is coated with a lithium cobaltate coating layer, and cobalt elements are distributed inside the lithium nickel composite oxide particles; the general formula of the lithium nickel composite oxide is Li a Ni 1-x-y Co x M y O2;

[0006] Wherein, 0.95 ≤ a ≤ 1.10, 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.005, and M includes at least one of Group 2 elements, Group 13 elements and transition metal elements, and does not include nickel and cobalt.

[0007] Further, inside the lithium nickel composite oxide particles, from the outside to the center, the molar content of cobalt element gradually decreases;

[0008] And / or, starting from the outer surface of the lithium nickel composite oxide particles and extending from the outside to the center, the reduction rate of the molar content of cobalt element is 0.025 mol% / μm - 0.3 mol% / μm.

[0009] Further, in the cathode material, the molar content of nickel > 94%;

[0010] And / or, the average particle size of the lithium nickel composite oxide particles is 3 μm - 17 μm.

[0011] The second aspect of the present application provides a method for preparing a positive electrode material. By coating a divalent cobalt compound, a trivalent cobalt compound, a lithium compound, and optionally an M compound on the surface of nickel hydroxide, and then performing sintering, doping of cobalt elements inside the material and coating on the surface are achieved simultaneously, effectively improving the safety and cycle stability of the high-nickel material.

[0012] The method for preparing a positive electrode material provided by the present application includes the following steps:

[0013] Coat a lithium compound, a cobalt compound, and optionally an M compound on the surface of nickel hydroxide, and then sinter the coated material under aerobic conditions to obtain a positive electrode material;

[0014] Among them, the cobalt compound includes a divalent cobalt compound and a trivalent cobalt compound.

[0015] Further, the molar content of the cobalt compound in the mixture of nickel hydroxide and the cobalt compound is 0.5%-5%;

[0016] And / or, the molar content of the trivalent cobalt compound in the cobalt compound is 50%-85%.

[0017] Further, the lithium compound, the cobalt compound, and optionally the M compound are coated on the surface of nickel hydroxide by solid-phase mixing;

[0018] And / or, the solid-phase mixing method includes mechanical mixing.

[0019] Further, the molar ratio of the sum of the amounts of substance of the lithium compound, the nickel hydroxide, the cobalt compound, and optionally the M compound to the lithium compound is 1:0.95-1.1;

[0020] And / or, the average particle size of the spherical nickel hydroxide is 3μm-17μm.

[0021] Further, the aerobic conditions include an aerobic atmosphere, and the oxygen content in the aerobic atmosphere is ≥98%;

[0022] And / or, the sintering temperature is 600°C-750°C, and the time is 8h-20h.

[0023] Further, the method for preparing the positive electrode material further includes washing, drying, and secondary sintering steps sequentially performed after sintering. Among them, the temperature of the secondary sintering is 250°C-700°C, and the time is 5h-15h.

[0024] The third aspect of the present application provides a positive electrode sheet or a battery including the positive electrode material provided by the first aspect or the positive electrode material obtained by the preparation method provided by the second aspect.

[0025] The present application has at least the following beneficial effects:

[0026] The positive electrode material provided by the present application has a lithium cobalt oxide coating layer on the outer surface of the lithium nickel composite oxide particles and cobalt elements are distributed inside, so that it can not only stabilize the crystal structure of the lithium nickel composite oxide, but also inhibit the side reaction between the material and the electrolyte, significantly improving the rate performance and cycle stability while increasing the lithium ion conductivity.

[0027] The method for preparing the positive electrode material provided by the present application coats a divalent cobalt compound, a trivalent cobalt compound, lithium hydroxide and an optional M compound on the surface of nickel hydroxide, and through high-temperature sintering, a positive electrode material is obtained in which part of the cobalt elements are coated on the surface of the lithium nickel oxide particles to form a uniform lithium cobalt oxide coating layer and part of the cobalt elements are distributed inside the lithium nickel composite oxide particles, effectively inhibiting the material phase change and the side reaction with the electrolyte, and significantly improving the rate performance and cycle stability of the material while increasing the lithium ion conductivity.

[0028] In addition, the method for preparing the positive electrode material provided by the present application is simple, stable, safe, and easy to be mass-produced industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a process flow chart of the preparation of the positive electrode material provided by the present application;

[0031] Figure 2 It is a schematic structural diagram of the positive electrode material provided in one solution of the present application;

[0032] Figure 3 It is a SEM diagram of the positive electrode material provided in Example 1 of the present application;

[0033] Figure 4 It is an XPS diagram of the positive electrode material provided in Example 1 of the present application;

[0034] Figure 5 It is an EDS scanning diagram of the positive electrode material provided in Example 1 of the present application;

[0035] Figure 6 It is an EDS scanning diagram of the positive electrode material provided in Comparative Example 1 of the present application;

[0036] Figure 7Capacity comparison chart of 2032 coin cells prepared using the cathode materials provided in Example 1 and Example 8 of the present application, respectively;

[0037] Figure 8 Impedance comparison chart of 2032 coin cells prepared using the cathode materials provided in Example 1 and Example 8 of the present application, respectively. Detailed implementation manners

[0038] The technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0039] At present, some researchers use the method of mixing and sintering a precursor and a lithium compound to obtain a LiNiMO2 compound, and then perform mixing and coating by a liquid phase or solid phase method to obtain a Co-coated high-nickel cathode material. The Co coating layer is mainly concentrated near the surface of the lithium nickel compound, and no effective coating layer is formed at the grain boundaries inside the material, and it is easy to form an MO oxide coating layer on the surface of the material, increasing the impedance of the material, reducing the rate performance of the material, and affecting the performance and internal resistance growth rate of the material after long-term cycling. In order to reduce the impedance of the material and improve the rate performance of the material, a first aspect of the present application provides a cathode material, including lithium nickel composite oxide particles, the outer surface of the lithium nickel composite oxide particles is coated with a lithium cobaltate coating layer, and cobalt elements are distributed inside the lithium nickel composite oxide particles; the general formula of the lithium nickel composite oxide is Li a Ni 1-x- y Co x M y O2;

[0040] wherein, 0.95 ≤ a ≤ 1.10, 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.005, and M includes at least one of Group 2 elements, Group 13 elements, and transition metal elements, and does not include nickel and cobalt.

[0041] Typically but not restrictively, a is, for example, 0.95, 0.98, 1, 1.02, 1.05, 1.08 or 1.1; x is, for example, 0, 0.01, 0.02, 0.03, 0.04 or 0.05; y is, for example, 0, 0.001, 0.002, 0.003, 0.004 or 0.005.

[0042] Typically but not restrictively, M is selected from at least one of Mg, Ca, Sr, Ba, B, Al, Ga, In, TI, Mn, Fe, Cu, Zn, Mo, Ce and Zr.

[0043] The positive electrode material provided by this application has lithium cobaltate coated on the surface of lithium nickel composite oxide particles, thereby effectively inhibiting the side reaction between the lithium nickel composite oxide particles and the electrolyte and improving the lithium ion conductivity. With cobalt elements distributed inside the lithium nickel composite oxide particles, lithium cobaltate or lithium cobalt M is formed at the grain boundaries, stabilizing the crystal structure of the lithium nickel composite oxide, and thus effectively improving the rate performance and cycle stability of the positive electrode material.

[0044] In a preferred embodiment of this application, inside the lithium nickel composite oxide particles, from the outside to the center, the mass content of cobalt elements gradually decreases, which is conducive to the formation of lithium nickel cobaltate or lithium nickel cobalt M near the outer layer of the lithium nickel composite oxide particles, effectively stabilizing the crystal structure inside the lithium nickel composite oxide, inhibiting lithium nickel mixing, and thus effectively improving the structural stability of the positive electrode material.

[0045] In one embodiment of this application, starting from the outer surface of the lithium nickel composite oxide particles and extending from the outside to the center, the molar content of cobalt elements gradually decreases, and the reduction rate is 0.025 mol% / μm - 0.3 mol% / μm. This application controls the distribution of material Co. The Ni content is lower on the outside of the material, improving stability; the Ni content is higher inside the material, improving the material capacity. If the concentration gradient is too low, the above effects cannot be achieved, and if the concentration gradient is too large, it will cause lattice mismatch of the material, resulting in stress accumulation and the material being prone to cracking. Therefore, choosing the above concentration gradient is more conducive to stabilizing the crystal structure inside the lithium nickel composite oxide and improving the structural stability of the positive electrode material.

[0046] Typical but non-limiting, the reduction rate of the molar content of cobalt elements is, for example, 0.025 mol% / μm, 0.035 mol% / μm, 0.045 mol% / μm, 0.055 mol% / μm, 0.08 mol% / μm, 0.1 mol% / μm, 0.15 mol% / μm, 0.2 mol% / μm, 0.25 mol% / μm or 0.30 mol% / μm.

[0047] In a preferred embodiment of this application, in the positive electrode material, the molar content of nickel > 94%, which is conducive to the positive electrode material provided by this application having a higher capacity advantage. This application adjusts the Ni content by controlling the Co content, which is operable.

[0048] The above-mentioned molar content of nickel refers to the proportion of the molar content of nickel elements in the positive electrode material, calculated based on the sum of the amounts of substances of nickel, lithium, cobalt, and optionally element M being 100%.

[0049] Typical but non-limiting, in the positive electrode material provided by this application, the molar content of nickel is, for example, 94.1%, 94.2%, 94.5%, 94.8%, 95%, 95.5% or 96%.

[0050] In one embodiment of the present application, the average particle size of the lithium nickel composite oxide particles is 3 μm - 17 μm to facilitate uniform distribution in the positive electrode sheet.

[0051] Typically but not restrictively, the average particle size of the lithium nickel composite oxide particles is, for example, 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm or 17 μm.

[0052] In one embodiment of the present application, the thickness of the lithium cobalt oxide coating layer on the surface of the lithium nickel composite oxide particles is 20 nm - 200 nm, so as to reduce the material impedance, ensure the rate performance and cycle performance of the positive electrode material, while effectively suppressing the side reaction between the lithium nickel composite oxide and the electrolyte, and improving the lithium ion conductivity of the positive electrode material.

[0053] Typically but not restrictively, the thickness of the lithium cobalt oxide coating layer is, for example, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 150 nm, 180 nm or 200 nm.

[0054] The second aspect of the present application provides a method for preparing a positive electrode material, including the following steps (as Figure 1 shown):

[0055] S100. Coating a lithium compound, a cobalt compound and an optional M compound on the surface of nickel hydroxide;

[0056] S200. Sintering the coated material under aerobic conditions to obtain the positive electrode material;

[0057] wherein, the M includes at least one of Group 2 elements, Group 13 elements and transition metal elements, and does not include nickel and cobalt;

[0058] The cobalt compound includes a divalent cobalt compound and a trivalent cobalt compound.

[0059] [M compound]

[0060] In the present application, M includes at least one of Group 2 elements, Group 13 elements and transition metal elements, and does not include nickel and cobalt.

[0061] Typically but not restrictively, M is selected from at least one of Mg, Ca, Sr, Ba, B, Al, Ga, In, TI, Mn, Fe, Cu, Zn, Mo, Ce and Zr.

[0062] In this application, by adding M compound to the raw materials to coat nickel hydroxide to form a lithium nickel M ternary material, the phase change of the material is further inhibited while the cell shrinkage is inhibited, a stable lithium ion transmission channel is provided, the cycle stability and thermal stability of the material are improved, and the material structure is stabilized.

[0063] In one embodiment of this application, the M compound includes, but is not limited to, one or a mixture of several of M oxide, M hydroxide, or M phosphate.

[0064] [Cobalt compound]

[0065] In this application, the cobalt compound includes divalent cobalt compound and trivalent cobalt compound.

[0066] In this application, nickel hydroxide is coated by divalent cobalt compound and trivalent cobalt compound together. The divalent cobalt has higher reaction activity and is more likely to diffuse into the interior of nickel hydroxide during the sintering process to form a lithium nickel cobaltate or lithium nickel M cobaltate solid solution oxide, stabilizing the crystal structure inside the lithium nickel composite oxide particles and inhibiting lithium nickel mixing. While the trivalent cobalt tends to coat on the surface of lithium nickelate particles to form a cobaltate coating layer, inhibiting side reactions of the material and improving the lithium ion conductivity of the positive electrode material.

[0067] In some embodiments of this application, the molar content of the trivalent cobalt compound in the cobalt compound is 50%-85%.

[0068] The molar content of the trivalent cobalt compound will affect the thickness of the coating layer and the crystal structure stability inside the lithium nickel composite oxide particles. If the molar content of the trivalent cobalt compound is too low, during the sintering process, more Co elements are doped into the interior of the lithium nickelate particles, resulting in a reduced coating effect of the material. If the molar content of the trivalent cobalt compound is too high, insufficient Co elements enter the interior of the lithium nickel composite oxide particles, and insufficient lithium nickel cobaltate or lithium nickel M cobaltate solid solution oxide can be formed, unable to effectively inhibit lithium nickel mixing. At the same time, it will also cause the coating layer to be too thick, increasing the impedance of the material and affecting the rate performance of the material.

[0069] Through multiple experiments, it is proved that when the molar content of the trivalent cobalt compound in the cobalt compound is 50%-85%, it can not only form a coating layer with a moderate thickness on the outer surface of the lithium nickel composite oxide particles, but also ensure the content of Co elements entering the interior of the lithium nickel composite oxide particles, thereby effectively inhibiting lithium nickel mixing and improving the cycle stability of the positive electrode material.

[0070] In this application, a cobaltate coating layer is formed by coating Co elements on the surface of the lithium nickel composite oxide particles, improving the lithium ion conductivity of the positive electrode material, forming a high lithium ion conductivity network, enhancing the rate performance of the material, and inhibiting side reactions between the material and the electrolyte.

[0071] Typically but not limited to, in the present application, the molar content of the trivalent cobalt compound in the cobalt compound is, for example, 50%, 60%, 65%, 70%, 75%, 80% or 85%.

[0072] In one aspect of the present application, the divalent cobalt compound includes but is not limited to at least one of divalent cobalt oxide, divalent cobalt hydroxide and divalent cobalt oxyhydroxide; the trivalent cobalt includes but is not limited to at least one of trivalent cobalt oxide, trivalent cobalt hydroxide and trivalent cobalt oxyhydroxide.

[0073] The preparation method of the positive electrode material provided by the present application is simple, stable and safe, and is easy to be mass-produced industrially. The scheme of co-coating spherical nickel hydroxide with the divalent cobalt compound and the trivalent cobalt compound and then sintering not only can form a uniform lithium cobaltate coating layer on the surface of the lithium nickelate particles, but also can form cobalt doping inside the lithium nickelate particles, which can effectively inhibit the phase change of the material and the side reaction with the electrolyte, and significantly improve the rate performance, cycle stability and capacity advantage of the material.

[0074] [Dosage of cobalt compound]

[0075] In the present application, after the cobalt compound, the lithium compound and optionally the M compound are coated on the surface of nickel hydroxide and then sintered, the cobalt element is distributed in a gradient manner on the surface coating and inside the lithium nickel composite oxide particles. The dosage of the cobalt compound will affect the thickness of the coating layer and the stability of the crystal structure of the lithium nickel composite oxide particles.

[0076] In a preferred aspect of the present application, the molar content of the cobalt compound in the mixture of the nickel hydroxide and the cobalt compound is 0.5% - 5%.

[0077] In the present application, the molar content of the cobalt compound in the nickel hydroxide and the cobalt compound refers to the ratio of the amount of substance of cobalt element in the cobalt compound to the sum of the amount of substance of nickel element in the nickel hydroxide and cobalt element in the cobalt compound, abbreviated as Co / (Co + Ni).

[0078] When Co / (Co + Ni) is higher than 5%, it will cause the coating layer on the surface of the lithium nickelate particles to be too thick, reduce the electronic conductivity of the material, increase the impedance of the material, and at the same time reduce the nickel content, resulting in a decrease in the capacity of the material. When Co / (Co + Ni) is lower than 0.5%, the content of Co element is too low to achieve the effect of simultaneously coating the surface of the lithium nickelate particles and doping inside the lithium nickelate particles to stabilize the crystal structure of the lithium nickelate particles.

[0079] Typically but not limited to, Co / (Co + Ni) is, for example, 0.5%, 0.75%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 3%, 4%, 4.5% or 5%.

[0080] Compared with the ternary material, as the Ni content increases, the Ni 2+ / 4+ redox pair increases, facilitating the release of more Li + ions, so the material capacity has a significant advantage.

[0081] [Lithium compound]

[0082] In one embodiment of the present application, the lithium compound includes but is not limited to lithium hydroxide, lithium carbonate, and a mixture of lithium hydroxide and lithium carbonate.

[0083] [Nickel hydroxide]

[0084] In one embodiment of the present application, spherical nickel hydroxide with an average particle size of 3 μm - 17 μm is selected as the raw material, which is more conducive to uniformly coating cobalt compounds, lithium hydroxide, and optionally M compounds on the surface of spherical nickel hydroxide by solid-phase mixing.

[0085] Typical but non-limiting, the average particle size of spherical nickel hydroxide is, for example, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, or 17 μm.

[0086] [Coating method]

[0087] In one embodiment of the present application, in step S100, the lithium compound, cobalt compound, and optionally M compound are coated on the surface of nickel hydroxide by solid-phase mixing. The process is simpler, the operation is more convenient, it is more suitable for large-scale production, and the production cost is reduced.

[0088] Optionally, the solid-phase mixing method includes mechanical mixing, and the mechanical mixing method includes but is not limited to mixing with a high-speed mixer.

[0089] [Aerobic condition]

[0090] In one embodiment of the present application, the aerobic condition includes an aerobic atmosphere, and the oxygen content in the aerobic atmosphere is ≥ 98%, which is conducive to the participation of oxygen in the reaction during the sintering process.

[0091] [Sintering condition]

[0092] In one embodiment of the present application, the sintering temperature is 600 °C - 750 °C, and the time is 8 h - 20 h, which is conducive to preparing a cathode material in which cobalt elements are doped both inside and on the surface of lithium nickel composite oxide particles.

[0093] Typical but non-limiting, the sintering temperature is, for example, 600 °C, 620 °C, 650 °C, 680 °C, 700 °C, 720 °C, or 750 °C, and the sintering time is, for example, 8 h, 9 h, 10 h, 12 h, 15 h, 18 h, or 20 h.

[0094] In one embodiment of the present application, the molar ratio of the sum of the amounts of nickel hydroxide, cobalt compound, and optional M compound to the lithium compound is 1:0.95 - 1.1.

[0095] The sum of the amounts of the above-mentioned nickel hydroxide, cobalt compound, and optional M compound refers to the sum of the amounts of nickel element in nickel hydroxide, cobalt element (including divalent cobalt and trivalent cobalt) in cobalt compound, and M element in optional M compound, which is simply referred to as the sum of the amounts of Ni, Co, and optional M.

[0096] The amount of the above-mentioned lithium compound refers to the amount of lithium element in the lithium compound, which is simply referred to as the amount of Li.

[0097] By controlling the molar ratio of the sum of the amounts of Ni, Co, and optional M to Li to be 1:0.95 - 1.1, the prepared cathode material has a higher nickel content and a more stable structure.

[0098] Typically but not restrictively, the molar ratio of the sum of the amounts of Ni, Co, and optional M to Li is, for example, 1:0.95, 1:0.98, 1:1, 1:1.02, 1:1.05, 1:1.08, or 1:1.1.

[0099] In one embodiment of the present application, the preparation method of the cathode material further includes the steps of washing, drying, and secondary sintering in sequence after sintering. Among them, the temperature of the secondary sintering is 250°C - 700°C, and the time is 5h - 15h.

[0100] By washing, the residual lithium element and impurities on the surface of the cathode material obtained after sintering are removed, avoiding the influence of the residual lithium element on the high-temperature safety of the material. By secondary sintering, the structural stability of the material is further improved.

[0101] Optionally, distilled water, deionized water, or pure water is used to wash the sintered material.

[0102] Typically but not restrictively, the temperature of the secondary sintering is, for example, 250°C, 300°C, 350°C, 450°C, 500°C, 550°C, 600°C, 650°C, or 700°C, and the time of the secondary sintering is, for example, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or 15h.

[0103] Optionally, the secondary sintering is also carried out under aerobic conditions, and the aerobic condition is that the oxygen content ≥ 90%.

[0104] Optionally, the structural schematic diagram of the cathode material provided by the present application is as Figure 2 shown, fromFigure 2 It can be seen that the positive electrode material provided by this application has a core-shell structure, and the inner core is Li a Ni 1-x-y Co x M y O2, and the shell layer is lithium cobaltate.

[0105] The third aspect of this application provides a positive electrode sheet or a battery including the positive electrode material provided in the first aspect above or the positive electrode material obtained by the preparation method provided in the second aspect.

[0106] For the convenience of those skilled in the art to understand, the technical solutions provided by this application will be further described below in conjunction with examples and comparative examples.

[0107] Example 1

[0108] This example provides a positive electrode material, which is prepared according to the following steps:

[0109] (1) Weigh Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O according to the ratio that the molar amount of Li is 1.05 times the sum of the molar amounts of Ni and Co, where Co accounts for 0.015 of the total molar amount of Ni+Co, CoOOH accounts for 65% of the total molar amount of Co(OH)2 and CoOOH, and Ni(OH)2 is spherical nickel hydroxide with a particle size of 10-15μm;

[0110] (2) Use a high-speed mixer to mix Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O, and sinter the mixture at 680°C for 10h in an atmosphere with an oxygen content ≥98% to obtain a cobalt-coated ultra-high nickel lithium nickel cobalt composite oxide;

[0111] (3) Wash the cobalt-coated ultra-high nickel lithium nickel cobalt composite oxide with deionized water, then filter it under pressure, and place the filter cake in a vacuum drying oven to dry at 200°C for 12h;

[0112] (4) Secondarily sinter the dried material at 600°C for 8h in an atmosphere with an oxygen content ≥90% to obtain the positive electrode material.

[0113] Example 2

[0114] This example provides a positive electrode material, which is prepared according to the following steps:

[0115] (1) Weigh Ni(OH)2, CoO, Co2O3, and LiOH·H2O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05. Among them, Co accounts for 0.015 of the total molar amount of Ni + Co, Co2O3 accounts for 65% of the total molar amount of CoO and Co2O3, and Ni(OH)2 is spherical nickel hydroxide with a particle size of 3 - 10 μm;

[0116] (2) Use a high - speed mixer to mix Ni(OH)2, CoO, Co2O3, and LiOH·H2O. Sinter the mixture at 650 °C for 12 h in an atmosphere with an oxygen content ≥ 98% to obtain cobalt - coated ultra - high - nickel lithium nickel cobalt composite oxide.

[0117] (3) Wash the cobalt - coated ultra - high - nickel lithium nickel cobalt composite oxide with deionized water, then filter it under pressure. Place the filter cake in a vacuum oven and dry it at 200 °C for 12 h.

[0118] (4) Secondary - sinter the dried material at 650 °C for 5 h in an atmosphere with an oxygen content ≥ 90% to obtain the cathode material.

[0119] Example 3

[0120] This example provides a cathode material, which is prepared according to the following steps:

[0121] (1) Weigh Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05. Among them, Co accounts for 0.015 of the total molar amount of Ni + Co, CoOOH accounts for 85% of the total molar amount of Co(OH)2 and CoOOH, and Ni(OH)2 is spherical nickel hydroxide with a particle size of 12 - 17 μm;

[0122] (2) Use a high - speed mixer to mix Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O. Sinter the mixture at 700 °C for 10 h in an atmosphere with an oxygen content ≥ 98% to obtain cobalt - coated ultra - high - nickel lithium nickel cobalt composite oxide.

[0123] (3) Wash the cobalt - coated ultra - high - nickel lithium nickel cobalt composite oxide with deionized water and then filter it under pressure. Place the filter cake in a vacuum oven and dry it at 200 °C for 12 h.

[0124] (4) Secondary - sinter the dried material at 550 °C for 12 h in an atmosphere with an oxygen content ≥ 90% to obtain the cathode material.

[0125] Example 4

[0126] This example provides a cathode material, which is prepared according to the following steps:

[0127] (1) Weigh Ni(OH)₂, Co(OH)₂, CoOOH, Al(OH)₃, and LiOH·H₂O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05. Among them, Co accounts for 0.015 of the total molar amount of Ni + Co, CoOOH accounts for 65% of the total molar amount of Co(OH)₂ and CoOOH, Ni(OH)₂ is spherical nickel hydroxide with a particle size of 10 - 15 μm, and the Al content is 0.1% of the total mass of the raw materials;

[0128] (2) Use a high - speed mixer to mix Ni(OH)₂, Co(OH)₂, CoOOH, Al(OH)₃, and LiOH·H₂O. Sinter the mixture at 680 °C for 10 h in an atmosphere with an oxygen content ≥ 98% to obtain cobalt - coated ultra - high nickel - lithium nickel - cobalt composite oxide.

[0129] (3) Wash the cobalt - coated ultra - high nickel - lithium nickel - cobalt composite oxide with deionized water and then filter - press it. Place the filter cake in a vacuum oven and dry it at 200 °C for 12 h.

[0130] (4) Sinter the dried material at 600 °C for 10 h in an atmosphere with an oxygen content ≥ 90% to obtain the positive electrode material.

[0131] Example 5

[0132] This example provides a positive electrode material, which is prepared according to the following steps:

[0133] (1) Weigh Ni(OH)₂, Co(OH)₂, CoOOH, and LiOH·H₂O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.05. Among them, Co accounts for 0.035 of the total molar amount of Ni + Co, CoOOH accounts for 65% of the total molar amount of Co(OH)₂ and CoOOH, and Ni(OH)₂ is spherical nickel hydroxide with a particle size of 10 - 15 μm;

[0134] (2) Use a high - speed mixer to mix Ni(OH)₂, Co(OH)₂, CoOOH, and LiOH·H₂O. Sinter the mixture at 680 °C for 10 h in an atmosphere with an oxygen content ≥ 98% to obtain cobalt - coated ultra - high nickel - lithium nickel - cobalt composite oxide.

[0135] (3) Wash the cobalt - coated ultra - high nickel - lithium nickel - cobalt composite oxide with deionized water and then filter - press it. Place the filter cake in a vacuum oven and dry it at 200 °C for 12 h.

[0136] (4) Sinter the dried material at 600 °C for 10 h in an atmosphere with an oxygen content ≥ 90% to obtain the positive electrode material.

[0137] Example 6

[0138] This example provides a cathode material, which is prepared according to the following steps:

[0139] (1) Weigh Ni(OH)2, Co(OH)2, CoOOH, Sr(OH)2 and LiOH·H2O according to the ratio that the molar amount of Li to the sum of the molar amounts of Ni and Co is 1.05, where Co accounts for 0.035 of the total molar amount of Ni+Co, CoOOH accounts for 50% of the total molar amount of Co(OH)2 and CoOOH, Ni(OH)2 is spherical nickel hydroxide with a particle size of 10-15μm;

[0140] (2) Mix Ni(OH)2, Co(OH)2, CoOOH, Sr(OH)2 and LiOH·H2O using a high-speed mixer, sinter the mixture at 680°C for 10h in an atmosphere with an oxygen content ≥98% to obtain cobalt-coated ultra-high nickel lithium nickel cobalt composite oxide.

[0141] (3) Wash the cobalt-coated ultra-high nickel lithium nickel cobalt composite oxide with deionized water and then filter it under pressure. Place the filter cake in a vacuum oven and dry it at 200°C for 12h.

[0142] (4) Sinter the dried material at 600°C for 10h in an atmosphere with an oxygen content ≥90% to obtain the cathode material.

[0143] Example 7

[0144] This example provides a cathode material, which is prepared according to the following steps:

[0145] (1) Weigh Ni(OH)2, Co(OH)2, CoOOH, LiOH·H2O according to the ratio that the molar amount of Li to the sum of the molar amounts of Ni and Co is 1.1, where Co accounts for 0.015 of the total molar amount of Ni+Co, CoOOH accounts for 65% of the total molar amount of Co(OH)2 and CoOOH, Ni(OH)2 is spherical nickel hydroxide with a particle size of 10-15μm;

[0146] (2) Mix Ni(OH)2, Co(OH)2, CoOOH and LiOH·H2O using a high-speed mixer, sinter the mixture at 680°C for 10h in an atmosphere with an oxygen content ≥98% to obtain cobalt-coated ultra-high nickel lithium nickel cobalt composite oxide.

[0147] (3) Wash the cobalt-coated ultra-high nickel lithium nickel cobalt composite oxide with deionized water and then filter it under pressure. Place the filter cake in a vacuum oven and dry it at 200°C for 12h.

[0148] (4) The dried material is subjected to secondary sintering at 600 °C for 10 h in an atmosphere with an oxygen content of ≥90% to obtain the cathode material.

[0149] Example 8

[0150] This example provides a cathode material. The difference in its preparation method from that of Example 1 lies in that in step (1), Co accounts for 10% of the total molar amount of Ni + Co, and the remaining steps are the same as those in Example 1, which will not be elaborated here.

[0151] Example 9

[0152] This example provides a cathode material, which is prepared according to the following steps:

[0153] (1) Weigh Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 0.95. Among them, Co accounts for 0.015 of the total molar amount of Ni + Co, CoOOH accounts for 65% of the total molar amount of Co(OH)2 and CoOOH, and Ni(OH)2 is spherical nickel hydroxide with a particle size of 10 - 15 μm;

[0154] (2) Use a high - speed mixer to mix Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O, and sinter the mixture at 680 °C for 10 h in an atmosphere with an oxygen content of ≥98% to obtain the cathode material.

[0155] Example 10

[0156] This example provides a cathode material, which is prepared according to the following steps:

[0157] (1) Weigh Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O according to the ratio of the molar amount of Li to the sum of the molar amounts of Ni and Co being 1.0. Among them, Co accounts for 0.015 of the total molar amount of Ni + Co, CoOOH accounts for 65% of the total molar amount of Co(OH)2 and CoOOH, and Ni(OH)2 is spherical nickel hydroxide with a particle size of 10 - 15 μm;

[0158] (2) Use a high - speed mixer to mix Ni(OH)2, Co(OH)2, CoOOH, and LiOH·H2O, and sinter the mixture at 680 °C for 10 h in an atmosphere with an oxygen content of ≥98% to obtain the cathode material.

[0159] Comparative Example 1

[0160] This comparative example provides a cathode material. The difference in its preparation method from that of Example 1 lies in that in step (1), CoOOH accounts for 10% of the total molar amount of Co(OH)2 and CoOOH, and the remaining steps are the same as those in Example 1, which will not be elaborated here.

[0161] Comparative Example 2

[0162] This comparative example provides a cathode material. The difference in its preparation method from that of Example 1 lies in that in step (1), CoOOH accounts for 95% of the total molar amount of Co(OH)2 and CoOOH, and the remaining steps are the same as those in Example 1, which will not be elaborated here.

[0163] Comparative Example 3

[0164] This comparative example provides a cathode material. The difference in its preparation method from that of Example 1 lies in that in step (1), all Co compounds in the raw materials are Co(OH)2, and trivalent cobalt compounds are not used in the raw materials. The remaining steps are the same as those in Example 1, which will not be elaborated here.

[0165] Comparative Example 4

[0166] This comparative example provides a cathode material. The difference in its preparation method from that of Example 1 lies in that in step (1), all Co compounds in the raw materials are CoOOH, and divalent cobalt compounds are not used in the raw materials. The remaining steps are the same as those in Example 1, which will not be elaborated here.

[0167] Comparative Example 5

[0168] This comparative example provides a cathode material. The difference in its preparation method from that of Example 1 lies in that in step (1), cobalt compounds are not used in the raw materials, and Ni(OH)2 and LiOH·H2O are weighed according to the ratio that the sum of the molar amounts of Li and Ni is 1.05. The remaining steps are the same as those in Example 1, which will not be elaborated here.

[0169] Test Example 1

[0170] The surface morphologies of the cathode materials provided in Examples 1 - 10 and Comparative Examples 1 - 5 were respectively tested by a Hitachi S4800 scanning electron microscope to measure the particle size of the cathode materials and the thickness of the surface coating layer. The results are shown in Table 1 below.

[0171] Table 1

[0172] Particle size distribution D50 (μm) Coating layer thickness (nm) Example 1 10.2 27 Example 2 4.5 52 Example 3 13.5 31 Example 4 10.3 36 Example 5 10.5 67 Example 6 10.2 58 Example 7 10.7 30 Example 8 10.4 143 Example 9 10.6 29 Example 10 10.5 31 Comparative Example 1 10.4 9 Comparative Example 2 10.2 42 Comparative Example 3 10.5 11 Comparative Example 4 10.8 49 Comparative Example 5 10.3 /

[0173] Figure 3 SEM image of the cathode material provided for Example 1. From Figure 3 it can be seen that the particle size of the cathode material provided in Example 1 is 3 - 17 μm, and the coating layer thickness is about 27 nm.

[0174] Test Example 2

[0175] The cathode materials provided in Examples 1-10 and Comparative Examples 1-5 were respectively subjected to XPS tests. It can be seen from the XPS spectra that the coating layers outside the cathode materials provided in Examples 1-10 and Comparative Examples 1-5 are all lithium cobaltate.

[0176] Figure 4 The XPS diagram of the cathode material provided for Example 1, from Figure 4 it can be seen that the coating layer on the surface of the cathode material provided for Example 1 is lithium cobaltate.

[0177] Test Example 3

[0178] The cathode materials provided in Examples 1-10 and Comparative Examples 1-5 were subjected to EDS tests, and the results are shown in Table 2. Among them, starting from the lithium nickel composite oxide and extending from the outside to the inside, the Co contents at 0 μm, 1 μm, 2 μm, 4 μm, and 8 μm inside the lithium nickel composite were respectively tested. In view of the fact that the particle sizes of the lithium nickel composite oxides inside some cathode materials are less than 16 μm, the lithium nickel composite oxides with particle sizes of more than 16 μm were selected for the internal Co content test in this test.

[0179] Table 2

[0180]

[0181] Figure 5 The EDS diagram of the cathode material provided for Example 1, from Figure 5 it can be seen that there is cobalt element distributed in the cathode material, and from the outside to the inside, the content of cobalt element gradually decreases.

[0182] Figure 6 The EDS diagram of the cathode material provided for Comparative Example 1, from Figure 6 it can be seen that there is cobalt element distributed in the cathode material provided for Comparative Example 1, and from the outside to the inside, the content of cobalt element remains stable.

[0183] Test Example 3

[0184] The cathode materials provided in Examples 1-10 and Comparative Examples 1-5 were respectively used as cathode materials to prepare 2032-type button cells. The specific preparation method is as follows: The cathode material, conductive carbon SP, and PVDF (polyvinylidene fluoride) were added to NMP (N-methylpyrrolidone) according to a mass ratio of 96:2:2, stirred to obtain a slurry, and the slurry was coated on an aluminum foil and dried to obtain a cathode sheet. A lithium sheet was used as the anode sheet to prepare a 2032-type button cell.

[0185] The positive electrode materials provided in Examples 1-10 and Comparative Examples 1-5 were tested for Ni content. The test steps were as follows: Weigh 1 g of the positive electrode material, digest it with nitric acid, make up the volume to 100 mL, and then dilute it 200 times. The element content was tested by a PE8000S type reaction coupled plasma instrument. The results are shown in Table 1.

[0186] The positive electrode materials provided in Examples 1-10 and Comparative Examples 1-5 were used as positive electrode materials to prepare 2032 type button cells respectively. Then, the above 2032 type button cells were respectively tested for the first-week specific capacity at 0.1C, rate performance, and 50-week cycle retention rate. The results are shown in Table 3 below.

[0187] Among them, the test method for the first-week specific capacity at 0.1C was as follows: Charge and discharge the 2032 type button cell at 0.1C / 0.1C between 25°C and 3.0V to 4.3V to test the first-week specific capacity.

[0188] The test method for the rate performance was as follows:

[0189] After testing the first week of the 2032 type button cell between 25°C and 3.0V to 4.3V, charge and discharge it at 0.5C / 0.5C, 0.5C / 1C, and 0.5C / 2C for one week each to measure the rate performance.

[0190] The test method for the 50-week cycle retention rate was as follows: Charge and discharge the 2032 type button cell at 0.5C / 1C between 25°C and 3.0V to 4.3V to test the cycle performance.

[0191] Table 3

[0192]

[0193]

[0194] It can be seen from the data of Examples 1-10 in Table 3 that the positive electrode materials prepared by the preparation method provided in this application have excellent rate performance and good cycle performance.

[0195] It can be seen from the data comparison between Examples 1-7 and 9-10 and Example 8 that when the molar content of the cobalt compound in the mixture of nickel hydroxide and the cobalt compound is 0.5-5%, the prepared positive electrode material has a higher Ni content, a smaller impedance, and a higher capacity.

[0196] Figure 7 It is a capacity comparison chart of 2032 type button cells prepared by using the positive electrode materials provided in Example 1 and Example 8 of this application as positive electrode materials respectively; Figure 8Impedance comparison diagram of 2032 coin cells prepared by using the cathode materials provided in Embodiment 1 and Embodiment 8 of the present application as cathode materials respectively; from the data combination of Embodiment 1 and Embodiment 8 Figure 7 and Figure 8 From the analysis and comparison, it can be seen that the decrease in Ni content reduces the capacity of the material. At the same time, the increase in Co content leads to an overly thick coating layer, reducing the electronic conductivity of the material, increasing the impedance of the material, and reducing the rate and cycle performance of the material.

[0197] From the data comparison between Embodiment 1 and Comparative Example 1, it can be seen that the decrease in the content of trivalent cobalt in the raw materials will cause more cobalt elements to be doped into the interior of the material, and the coating layer on the surface of the material is insufficient, which is not conducive to suppressing the side reaction between the material and the electrolyte, and reduces the cycle stability of the material.

[0198] From the data comparison between Embodiment 1 and Comparative Example 5, it can be seen that the cobalt-free coated cathode material has a higher capacity, but due to the lack of cobalt doping and coating effects, the rate and cycle performance of the material are significantly reduced.

[0199] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A cathode material, characterized in that, It includes lithium nickel composite oxide particles, the outer surface of the lithium nickel composite oxide particles is coated with a lithium cobalt oxide coating layer, and cobalt elements are distributed inside the lithium nickel composite oxide particles; the general formula of the lithium nickel composite oxide is Li a Ni 1-x-y Co x M y O2; Among them, 0.95 ≤ a ≤ 1.10, 0 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.005, and M includes at least one of Group 2 elements, Group 13 elements, and transition metal elements, and does not include nickel and cobalt; Inside the lithium nickel composite oxide particles, from the outside to the center, the molar content of cobalt element gradually decreases; The method for preparing the positive electrode material includes the following steps: Coating a lithium compound, a cobalt compound, and an optional M compound on the surface of nickel hydroxide, and then sintering the coated material under aerobic conditions to obtain the positive electrode material; Among them, the cobalt compound includes a divalent cobalt compound and a trivalent cobalt compound; The molar content of the cobalt compound in the mixture of nickel hydroxide and the cobalt compound is 0.5% - 5%; The molar content of the trivalent cobalt compound in the cobalt compound is 50% - 85%.

2. The cathode material according to claim 1, characterized in that, Starting from the outer surface of the lithium nickel composite oxide particles and extending from the outside to the center, the reduction rate of the molar content of cobalt element is 0.025 mol% / μm - 0.3 mol% / μm.

3. The cathode material according to claim 1, characterized in that, The average particle size of the lithium nickel composite oxide particles is 3 μm - 17 μm; And / or, the thickness of the lithium cobaltate coating layer is 20 nm - 200 nm.

4. The preparation method of the cathode material according to any one of claims 1-3, characterized in that, Including the following steps: Coating a lithium compound, a cobalt compound, and an optional M compound on the surface of nickel hydroxide, and then sintering the coated material under aerobic conditions to obtain the positive electrode material; Among them, the cobalt compound includes a divalent cobalt compound and a trivalent cobalt compound; The molar content of the cobalt compound in the mixture of nickel hydroxide and the cobalt compound is 0.5% - 5%; The molar content of the trivalent cobalt compound in the cobalt compound is 50% - 85%.

5. The preparation method of the cathode material according to claim 4, wherein, The lithium compound, the cobalt compound, and the optional M compound are coated on the surface of nickel hydroxide by solid-phase mixing; And / or, the solid-phase mixing method includes mechanical mixing.

6. The preparation method of the cathode material according to claim 4, wherein, The molar ratio of the sum of the amounts of substances of nickel hydroxide, cobalt compound, and optional M compound to the lithium compound is 1:0.95 - 1.1; And / or, the nickel hydroxide is spherical, and the average particle size is 3 μm - 17 μm.

7. The preparation method of the cathode material according to claim 4, characterized in that, The aerobic conditions include an aerobic atmosphere, and the oxygen content in the aerobic atmosphere is ≥ 98%; And / or, the sintering temperature is 600 °C - 750 °C, and the time is 8 h - 20 h.

8. The preparation method of the cathode material according to any one of claims 4-7, characterized in that, It also includes the steps of washing, drying, and secondary sintering carried out in sequence after sintering; among them, the temperature of the secondary sintering is 250 °C - 700 °C, and the time is 5 h - 15 h.

9. A positive electrode sheet or a battery including the positive electrode material according to any one of claims 1 - 3 or the positive electrode material obtained by the preparation method according to any one of claims 4 - 8.

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