A core-shell structured positive electrode precursor, a preparation method therefor, and use thereof

Abstract

The application provides a core-shell structure positive electrode precursor and a preparation method and use thereof. The core-shell structure positive electrode precursor comprises a precursor inner core and a precursor outer shell layer from inside to outside; the porosity of the precursor inner core is greater than that of the precursor outer shell layer, and primary grains in the precursor outer shell layer are arranged and distributed along a radial direction of the precursor outer shell layer. The core-shell structure positive electrode precursor provided by the application has high tap density and low impurity content, can significantly reduce the sintering temperature during preparation of a single-crystal positive electrode material, thereby effectively inhibiting lithium-nickel mixing in the positive electrode material, avoiding agglomeration of positive electrode material particles, improving the single-crystallinity of the positive electrode material, and improving the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a core-shell structured positive electrode precursor, its preparation method, and its uses. Background Technology

[0002] Ternary lithium-ion battery cathode materials have exhibited excellent comprehensive performance due to their combination of high energy density of nickel, excellent electrochemical performance of cobalt, and cost-effectiveness and safety of manganese, leading to their rapid development and application in recent years. Especially to meet the requirements of long driving range for pure electric vehicles, the nickel content in ternary cathode materials is increasing. However, with the increase in nickel content, the spherical nickel-cobalt-manganese hydroxide synthesized by traditional co-precipitation methods, after being calcined into polycrystalline cathode materials, is prone to a series of drawbacks when used in batteries, including poor crystallinity, excessive internal stress, increased irreversible charge-discharge reactions, severe gas generation, poor cycle performance, and poor stability. These drawbacks affect the overall performance and lifespan of the battery.

[0003] Single-crystal structures can effectively alleviate the structural instability of high-nickel ternary materials. Single-crystal particles possess a continuous crystal structure with fewer grain boundaries, fewer intracrystalline defects, and less lattice distortion. This allows lithium ions to diffuse rapidly and uniformly along the channels within the crystal during charging and discharging, thereby reducing interfacial side reactions and irreversible changes in the crystal structure, and improving the cycle stability and safety of ternary materials. Furthermore, single-crystal particles typically exhibit better mechanical strength and thermal stability, which helps resist stress and thermal shock generated during charging and discharging, reducing particle breakage and material degradation.

[0004] However, the preparation of single-crystal cathode materials requires a higher calcination temperature compared to polycrystalline materials, which exacerbates lithium-nickel mixing and is not conducive to obtaining excellent electrochemical performance.

[0005] Therefore, how to reduce the degree of lithium-nickel mixing in single-crystal cathode materials and improve the electrochemical performance of single-crystal cathode materials is an urgent technical problem to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a core-shell structured cathode precursor, its preparation method, and its applications. The core-shell structured cathode precursor provided by this invention has high tap density and low impurity content, which can significantly reduce the sintering temperature during the preparation of single-crystal cathode materials. This effectively suppresses lithium-nickel mixing in the cathode material, avoids particle agglomeration, improves the single crystallinity of the cathode material, and enhances the electrochemical performance of the battery.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a core-shell structured positive electrode precursor, wherein the core-shell structured positive electrode precursor comprises, from the inside to the outside, a precursor core and a precursor shell layer; the porosity of the precursor core is greater than the porosity of the precursor shell layer, and the primary grains in the precursor shell layer are oriented and distributed along the radial direction of the precursor shell layer.

[0009] The core-shell structured cathode precursor provided by this invention features a unique radial structure with high porosity and disordered primary grain arrangement in the core, and low porosity and oriented primary grain arrangement in the outer shell. This results in high tap density, allowing the core to easily shrink during solid-state sintering, thus promoting the breakage of spherical secondary particles and further facilitating the single-crystalization of the cathode material. Furthermore, the radially oriented primary grain arrangement in the outer shell facilitates mass transfer during sintering. This synergistic effect significantly reduces the sintering temperature when preparing single-crystal cathode material from the cathode precursor material, effectively suppressing lithium-nickel mixing in the cathode material and improving the electrochemical performance of the battery. Moreover, the loose core and radially oriented primary grain arrangement in the outer shell facilitate the removal of impurity ions such as sodium and sulfur during post-processing washing, further optimizing the quality of the precursor.

[0010] In this invention, if the primary grains in the outer shell layer are still randomly distributed, they cannot effectively promote the mass transfer process during sintering and cannot play the role of reducing the sintering temperature and thus suppressing lithium-nickel mixing. Furthermore, if the porosity of the core is lower than that of the outer shell layer, the precursor core will not be able to fully break down after sintering or will require a higher sintering temperature, making it impossible to obtain a single-crystal cathode material with good dispersion and low lithium-nickel mixing.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0012] Preferably, the median particle size D50 of the core-shell structured cathode precursor is 2 to 8 μm, such as 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm or 8 μm, and more preferably 3.5 to 6 μm.

[0013] Preferably, the median particle size D50 of the precursor core is 1.5 to 3 μm, such as 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm or 3 μm.

[0014] In a second aspect, the present invention provides a method for preparing a core-shell structured cathode precursor as described in the first aspect, the method comprising the following steps:

[0015] A mixed metal salt solution, a precipitant solution, and a complexing agent solution are subjected to a first coprecipitation reaction under a first oxidizing atmosphere to obtain a precursor core.

[0016] After obtaining the precursor core, an additive solution is added under a second oxidizing atmosphere to carry out a second coprecipitation reaction, thereby obtaining the core-shell structured cathode precursor.

[0017] Wherein, the oxygen concentration in the first oxidizing atmosphere is greater than the oxygen concentration in the second oxidizing atmosphere.

[0018] The preparation method provided by this invention first performs a first coprecipitation reaction under a strong oxidizing atmosphere to refine the primary grains, and then performs a second coprecipitation reaction with synergistic additives under a weak oxidizing atmosphere to induce the primary grains to grow in a radially oriented arrangement. This results in a core-shell structured cathode precursor with a special radial structure, characterized by high porosity in the core and disordered arrangement of primary grains, and low porosity in the shell and oriented arrangement of primary grains. Furthermore, the preparation method is simple to operate, requires no complex preparation process, and is suitable for large-scale production.

[0019] In this invention, if additives are added during the first coprecipitation reaction, a disordered and porous internal structure cannot be obtained, and the additives are easily trapped inside the particles and difficult to remove during rapid agglomeration after nucleation. If no additives are added during the second coprecipitation reaction, it is impossible to promote the formation of a directional arrangement of primary grains in the shell. Furthermore, if the oxygen concentration in the first oxidizing atmosphere is lower than that in the second oxidizing atmosphere, the porosity of the precursor core will be lower than that of the precursor shell, requiring a higher sintering temperature to obtain a single-crystal cathode material with better dispersion. That is, in the preparation method provided in this application, the first oxidizing atmosphere, the second oxidizing atmosphere, and the additives work synergistically to obtain a cathode precursor material with a special structure.

[0020] Preferably, the metal element in the mixed metal salt solution includes nickel.

[0021] Preferably, the metal element in the mixed metal salt solution further includes element M, which includes transition metal elements.

[0022] This invention does not specifically limit the type of substance of element M. It can be used for any transition metal element that can be used as a precursor material in layered oxide cathodes. The M includes, but is not limited to, at least one of manganese, cobalt, or aluminum.

[0023] Preferably, the molar percentage of nickel is 33% to 98%, based on the total molar amount of all metal elements in the metal mixed salt solution being 100%, for example, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 93%, 95%, or 98%, etc.

[0024] Preferably, the mixed gas in the first oxidizing atmosphere includes a first oxygen-containing gas and a first non-oxygen gas, and the volume ratio of the first oxygen-containing gas to the first non-oxygen gas is (0.3-3):1, for example, 0.3:1, 0.5:1, 0.8:1, 1:1, 1.3:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1 or 3:1, etc.

[0025] Preferably, the mixed gas in the second oxidizing atmosphere includes a second oxygen-containing gas and a second non-oxygen gas, and the volume ratio of the second oxygen-containing gas to the second non-oxygen gas is (0.02-0.2):1, for example, 0.02:1, 0.05:1, 0.08:1, 0.13:1, 0.15:1, 0.18:1 or 0.3:1, etc.

[0026] It should be noted that the types of the first oxygen-containing gas and the second oxygen-containing gas in this invention are independently including, but not limited to, air, oxygen, or ozone; the first non-oxygen gas and the second non-oxygen gas include, but are not limited to, protective gases, and the protective atmosphere includes nitrogen or other inert gases.

[0027] In this invention, by further adjusting the volume ratio of the first oxygen-containing gas to the first non-oxygen gas to (0.3-3):1 and / or the volume ratio of the second oxygen-containing gas to the second non-oxygen gas to (0.02-0.2):1, the pore structure and distribution of the precursor core and shell can be better adjusted, thereby achieving the optimized design of a precursor with a specific structure.

[0028] Preferably, the mass fraction of the additive in the additive solution is 0.1% to 10%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0029] In this invention, the mass fraction of the additive is controlled to be 0.1-10%, which is more conducive to promoting the primary grain orientation of the precursor shell while ensuring that no impurities are introduced, thereby improving the quality of the precursor.

[0030] Preferably, the additive comprises any one or a combination of at least two of polyvinylpyrrolidone, polyethylene glycol, tetramethylammonium hydroxide, hexadecyltrimethylammonium bromide, or triethanolamine.

[0031] Preferably, the reaction temperatures of the first coprecipitation reaction and the second coprecipitation reaction are each independently 40 to 80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C.

[0032] Preferably, the rotation speeds of the first coprecipitation reaction and the second coprecipitation reaction are each independently 300 to 800 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, or 800 rpm.

[0033] Preferably, the pH values ​​of the first coprecipitation reaction and the second coprecipitation reaction are each independently 10 to 11, such as 10, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9 or 11.

[0034] Preferably, after the second coprecipitation reaction is completed, washing and drying processes are performed sequentially.

[0035] Preferably, the water content of the core-shell structured cathode precursor is ≤0.8wt%.

[0036] As a preferred technical solution, the preparation method includes the following steps:

[0037] A mixed metal salt solution, a precipitant solution, and a complexing agent solution are subjected to a first coprecipitation reaction in a first oxidizing atmosphere of a mixture of a first oxygen-containing gas and a first non-oxygen gas, wherein the volume ratio of the first oxygen-containing gas to the first non-oxygen gas is (0.3-3):1, to obtain a precursor core.

[0038] After obtaining the precursor core, under a second oxidizing atmosphere of a mixture of a second oxygen-containing gas and a second non-oxygen gas, with a volume ratio of the second oxygen-containing gas to the second non-oxygen gas of (0.02-0.2):1, an additive solution with a mass fraction of 0.1-10% is added to carry out a second coprecipitation reaction to obtain the core-shell structured cathode precursor.

[0039] The metal mixed salt solution contains nickel and M elements, which include transition metal elements. The total molar amount of all metal elements in the metal mixed salt solution is 100%, and the molar amount of nickel is 33% to 98%.

[0040] It should be noted that, apart from the above-mentioned feature limitations, the specific types of raw materials and other preparation parameters in the preparation method provided by this invention are all conventional technical solutions, and those skilled in the art can make adaptive selections and adjustments according to actual needs.

[0041] Optionally, the metal mixed salt solution, precipitant solution, and complexing agent solution can be added to the reaction substrate in a co-current manner, or they can react directly. When the reaction substrate is present, it includes water, precipitant, and complexing agent. The pH value of the reaction substrate is 11.3 to 13, such as 11.3, 11.5, 11.8, 12, 12.3, 12.5, 12.8, or 13. The concentration of the complexing agent in the reaction substrate is 2 to 15 g / L, such as 2 g / L, 5 g / L, 10 g / L, or 15 g / L.

[0042] Optionally, the reaction process includes an unavoidable nucleation process under a first oxidizing atmosphere (during which the pH value can be adjusted to >11.3), where the nucleation process is when the particles are stable and no new particles appear, and the nucleation process ends when the particles begin to grow.

[0043] Optionally, the total concentration of metal ions in the mixed metal salt solution is 1 to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, etc., and the types of salts include at least one of sulfate, nitrate, chloride or acetate.

[0044] Optionally, the mass fraction of the precipitant solution is 20% to 40%, for example, 20%, 25%, 30%, 35% or 40%, etc., and the precipitant includes, but is not limited to, at least one of sodium hydroxide, potassium hydroxide or sodium carbonate;

[0045] Optionally, the complexing agent solution has a mass fraction of 10-25%, such as 10%, 15%, 20% or 25%, and the complexing agent includes, but is not limited to, ammonia or citric acid.

[0046] Optionally, the washing process uses conventional alkaline washing followed by water washing, with each washing cycle repeated two or more times to fully remove residual sodium and sulfur impurities.

[0047] Thirdly, the present invention provides a single-crystal cathode material, wherein the single-crystal cathode material is obtained by mixing and sintering a core-shell structured cathode precursor as described in the first aspect or a core-shell structured cathode precursor prepared by the preparation method described in the second aspect with a lithium source.

[0048] The single-crystal cathode material provided by this invention has a low degree of lithium-nickel mixing and excellent electrochemical performance.

[0049] Preferably, the sintering includes performing a first sintering, a second sintering, and a third sintering in sequence.

[0050] Preferably, the sintering atmosphere is an oxygen-containing atmosphere.

[0051] Preferably, the sintering temperature of the first sintering is 400 to 650°C, such as 400°C, 450°C, 500°C, 550°C, 600°C, or 650°C.

[0052] Preferably, the holding time for the first sintering is 3 to 10 hours, such as 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0053] Preferably, the sintering temperature of the second sintering is 880 to 1000°C, such as 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, or 1000°C.

[0054] Preferably, the holding time for the second sintering is 3 to 12 hours, such as 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or 13 hours, and more preferably 5 to 8 hours.

[0055] Preferably, the sintering temperature of the third sintering is 780-850℃, such as 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃ or 850℃.

[0056] In this invention, the temperature of the third sintering is lower than that of the second sintering. That is, the temperature is raised for sintering and then lowered for sintering. The purpose is to allow the precursor particles to be basically completely broken down under the high temperature of the second sintering, so that the growth of single crystal particles can continue at the slightly lower temperature of the third sintering. This avoids the aggravation of lithium-nickel mixing caused by being in an extremely high temperature environment for a long time.

[0057] Preferably, the holding time for the third sintering is 3 to 12 hours, such as 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or 13 hours, and more preferably 5 to 8 hours.

[0058] In this invention, the three-stage sintering process is more conducive to obtaining single-crystal cathode materials with low lithium-nickel mixing degree, good dispersibility and crystal form. The first sintering process fully removes water vapor and substances such as CO2 and H2O generated by the reaction from the mixture, avoiding the formation of micropores. The second sintering process causes the secondary spherical particles to fully break down under high temperature to form single-crystal primary particles with good dispersibility. The third sintering process is conducive to the development of the broken single-crystal primary particles into larger-sized single-crystal cathode materials with good crystal form.

[0059] Preferably, the heating rates of the first sintering and the second sintering are each independently 1 to 10 °C / min, for example 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, and more preferably 2 to 5 °C / min.

[0060] Preferably, the cooling rate of the third sintering is 1 to 10 °C / min, for example, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, and more preferably 2 to 5 °C / min.

[0061] It should also be noted that the type of lithium source, the amount of lithium source added, and the mixing method of the lithium source and the core-shell structured cathode precursor in this invention are all conventional technical solutions.

[0062] Optionally, the lithium source includes, but is not limited to, at least one of lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate;

[0063] Optionally, the ratio of the molar amount of lithium in the lithium source to the total molar amount of Me element (i.e., all metal elements in the cathode precursor material) in the core-shell structured cathode precursor is (1.04 to 1.2):1, for example, 1.04:1, 1.05:1, 1.08:1, 1.1:1, 1.12:1, 1.15:1 or 1.2:1, and more preferably (1.08 to 1.12):1;

[0064] Optionally, the mixing method can be either dry mixing or wet mixing;

[0065] Those skilled in the art can adjust the above preparation process according to actual needs.

[0066] Fourthly, the present invention also provides a battery comprising the single-crystal cathode material as described in the third aspect.

[0067] Due to space limitations and to avoid redundancy, this invention does not list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0068] Compared with the prior art, the present invention has the following beneficial effects:

[0069] (1) The core-shell structure of the cathode precursor provided by the present invention has a special radial structure with high porosity and disordered primary grains in the core and low porosity and oriented primary grains in the shell. It has a high tap density. During solid-state sintering, the core is prone to shrinkage, which promotes the breakage of spherical secondary particles and further promotes the single crystallization of the cathode material. The radial orientation of the primary grains in the shell is conducive to the mass transfer process during sintering. The synergistic effect can significantly reduce the sintering temperature when preparing single-crystal cathode material from cathode precursor material, thereby effectively suppressing the lithium-nickel mixing phenomenon in cathode material and improving the electrochemical performance of battery. At the same time, it also avoids the agglomeration of particles during cathode material preparation, resulting in high particle dispersion and high single crystallinity. Furthermore, the loose core and radial orientation of the primary grains in the shell are conducive to the removal of impurity ions such as sodium and sulfur during the washing process in the post-processing, further optimizing the quality of the precursor.

[0070] (2) The preparation method provided by the present invention first performs a first coprecipitation reaction under a strong oxidizing atmosphere to refine the primary grains, and then performs a second coprecipitation reaction with synergistic additives under a weak oxidizing atmosphere to induce the primary grains to grow radially oriented, thereby obtaining a positive electrode precursor material with a special radial structure in the precursor core with high porosity and disordered primary grain arrangement, and in the outer shell layer with low porosity and oriented primary grain arrangement; and the preparation method is simple to operate, does not require a complicated preparation process, and is suitable for large-scale production. Attached Figure Description

[0071] Figure 1 SEM image of the cross-section of the core-shell structured cathode precursor provided in Example 1.

[0072] Figure 2 SEM image of the single-crystal cathode material provided in Application Example 1.

[0073] Figure 3 SEM image of the cross-section of the core-shell structured cathode precursor provided for Comparative Example 1.

[0074] Figure 4 Compare the SEM images of the single-crystal cathode material provided in Application Example 1.

[0075] Figure 5 SEM images of the single-crystal cathode material provided in Application Example 2 are shown for comparison. Detailed Implementation

[0076] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0077] 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 application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0078] In the description of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0079] Example 1

[0080] This embodiment provides a core-shell structured cathode precursor, wherein the core-shell structured cathode precursor comprises, from the inside out, a precursor core Ni. 0.6 Co 0.2 Mn 0.2 (OH)2 and precursor outer shell Ni 0.6 Co 0.2 Mn 0.2 (OH)2; the porosity of the precursor core is greater than that of the precursor shell layer, and the primary grains in the precursor shell layer are oriented and distributed along the radial direction of the precursor shell layer.

[0081] The preparation method of the core-shell structured positive electrode precursor is as follows:

[0082] Step S1: According to the molecular formula Ni 0.6 Co 0.2 Mn 0.2 Prepare a nickel-cobalt-manganese mixed metal sulfate solution with (OH)2, the total metal ion concentration is 2 mol / L; prepare a 32% sodium hydroxide precipitant solution; prepare a 16% ammonia solution as a complexing agent; prepare an additive solution with a 5% additive concentration by mixing triethanolamine and pure water at a mass ratio of 5:95; prepare a reaction base solution with a pH of 12.0–12.3 and an ammonia concentration of 5–6 g / L using liquid alkali, concentrated ammonia, and 20 L of pure water.

[0083] Step S2: Under a strong oxidizing atmosphere (first oxidizing atmosphere) with a volume ratio of nitrogen (first non-oxygen gas) to air (second oxygen gas) of 1:1, the prepared mixed metal sulfate solution, sodium hydroxide solution, and ammonia solution are added to a 50L reactor containing the bottom liquid at a uniform flow rate of 1.86L / h, 0.76L / h, and 0.26L / h, respectively, at 380rpm for the first coprecipitation reaction at 50℃. The pH of the nucleation stage is controlled at 12.0±0.1 and maintained for 4h. Then, the feed flow rate of the alkali solution is gradually reduced to make the pH of the reaction system 10.6±0.2 to continue the first coprecipitation reaction. When the D50 reaches 2μm, the first stage of coprecipitation reaction ends, and the precursor nucleus is obtained.

[0084] The reaction atmosphere was adjusted to a weak oxidizing atmosphere (second oxidizing atmosphere) with a volume ratio of nitrogen (second non-oxygen gas) to air (second oxygen gas) of 1:0.08. 1 L of additive solution was slowly pumped in using a peristaltic pump. The reaction system was maintained at pH 10.6 ± 0.2 and an ammonia concentration of 5–6 g / L for the second co-precipitation reaction until the particle size D50 reached 4 μm. At this point, the feed was stopped, yielding Ni. 0.6 Co 0.2 Mn 0.2 (OH)2 precursor slurry;

[0085] After the slurry is allowed to stand and the supernatant is extracted, it is transferred to a washer and washed three times with alkali and three times with water using a 3% sodium hydroxide solution and hot pure water at 60°C, respectively. After solid-liquid separation, it is transferred to an oven and dried at 120°C to obtain the core-shell structured positive electrode precursor with a D50 of 4μm.

[0086] Example 2

[0087] This embodiment provides a core-shell structured cathode precursor, wherein the core-shell structured cathode precursor comprises, from the inside out, a precursor core Ni. 0.6 Co 0.2 Mn 0.2 (OH)2 and precursor outer shell Ni 0.6 Co 0.2 Mn 0.2 (OH)2; the porosity of the precursor core is greater than that of the precursor shell layer, and the primary grains in the precursor shell layer are oriented and distributed along the radial direction of the precursor shell layer.

[0088] The preparation method of the positive electrode precursor is as follows:

[0089] Step S1: According to the molecular formula Ni 0.6 Co 0.2 Mn 0.2Prepare a nickel-cobalt-manganese mixed metal sulfate solution with (OH)2, the total metal ion concentration being 1 mol / L; prepare a 20% (w / w) sodium hydroxide precipitant solution; prepare a 10% (w / w) ammonia solution as a complexing agent; prepare an additive solution with a 10% (w / w) additive concentration by mixing triethanolamine and pure water at a mass ratio of 10:90; prepare a reaction base solution with a pH of 12.0–12.3 and an ammonia concentration of 5–6 g / L using liquid alkali, concentrated ammonia, and 20 L of pure water;

[0090] Step S2: Under a strong oxidizing atmosphere with a volume ratio of nitrogen (first non-oxygen gas) to air (second oxygen gas) of 1:3, the prepared mixed metal sulfate solution, sodium hydroxide solution, and ammonia solution are added to a 50L reactor containing the bottom liquid at a uniform flow rate of 1.86 L / h, 0.76 L / h, and 0.26 L / h, respectively, at 380 rpm and 50°C for the first coprecipitation reaction. The pH of the nucleation stage is controlled at 12.0 ± 0.1 and maintained for 4 h. Then, the feed flow rate of the alkali solution is gradually reduced to make the pH of the reaction system 10.6 ± 0.2 to continue the first coprecipitation reaction. When the D50 reaches 3 μm, the first stage of coprecipitation reaction ends, and the precursor nucleus is obtained.

[0091] The reaction atmosphere was adjusted to a weakly oxidizing atmosphere with a volume ratio of nitrogen (a second non-oxygen gas) to air (a second oxygen gas) of 1:0.2. 1 L of additive solution was slowly pumped in using a peristaltic pump. The reaction system was maintained at pH 10.6 ± 0.2 and an ammonia concentration of 5–6 g / L for the second co-precipitation reaction until the particle size D50 reached 6 μm. At this point, the feed was stopped, yielding Ni. 0.6 Co 0.2 Mn 0.2 (OH)2 precursor slurry;

[0092] After the slurry is allowed to stand and the supernatant is extracted, it is transferred to a washer and washed three times with alkali and three times with water using a 3% sodium hydroxide solution and hot pure water at 60°C, respectively. After solid-liquid separation, it is transferred to an oven and dried at 120°C to obtain the core-shell structured positive electrode precursor with a D50 of 6μm.

[0093] Example 3

[0094] This embodiment provides a core-shell structured cathode precursor, wherein the core-shell structured cathode precursor comprises, from the inside out, a precursor core Ni. 0.6 Co 0.2 Mn 0.2 (OH)2 and precursor outer shell Ni 0.6 Co 0.2 Mn 0.2(OH)2; the porosity of the precursor core is greater than that of the precursor shell layer, and the primary grains in the precursor shell layer are oriented and distributed along the radial direction of the precursor shell layer.

[0095] The preparation method of the positive electrode precursor is as follows:

[0096] Step S1: According to the molecular formula Ni 0.6 Co 0.2 Mn 0.2 Prepare a nickel-cobalt-manganese mixed metal sulfate solution with (OH)2, the total metal ion concentration is 2 mol / L; prepare a 32% (w / w) sodium hydroxide precipitant solution; prepare a 16% (w / w) ammonia solution as a complexing agent; prepare an additive solution with a 1% (w / w) additive concentration by mixing triethanolamine and pure water at a mass ratio of 1:99; prepare a reaction base solution with a pH of 11.5–11.8 and an ammonia concentration of 5–6 g / L using liquid alkali, concentrated ammonia, and 20 L of pure water.

[0097] Step S2: Under a strong oxidizing atmosphere with a volume ratio of nitrogen (first non-oxygen gas) to air (second oxygen gas) of 1:0.3, the prepared mixed metal sulfate solution, sodium hydroxide solution, and ammonia solution are added to a 50L reactor containing the bottom liquid at a uniform flow rate of 1.86L / h, 0.76L / h, and 0.26L / h, respectively, at 300rpm for the first coprecipitation reaction at 40℃. The pH of the nucleation stage is controlled at 12.5±0.1 and maintained for 4h. Then, the feed flow rate of the alkali solution is gradually reduced to make the pH of the reaction system 10.3±0.2 to continue the first coprecipitation reaction. When the D50 reaches 2μm, the first stage of coprecipitation reaction ends, and the precursor nucleus is obtained.

[0098] The reaction atmosphere was adjusted to a weakly oxidizing atmosphere with a volume ratio of nitrogen (a second non-oxygen gas) to air (a second oxygen gas) of 1:0.02. 1 L of additive solution was slowly pumped in using a peristaltic pump. The reaction system was maintained at pH 10.3 ± 0.2 and an ammonia concentration of 5–6 g / L for the second co-precipitation reaction until the particle size D50 reached 4 μm. At this point, the feed was stopped, yielding Ni. 0.6 Co 0.2 Mn 0.2 (OH)2 precursor slurry;

[0099] After the slurry is allowed to stand and the supernatant is extracted, it is transferred to a washer and washed three times with alkali and three times with water using a 3% sodium hydroxide solution and hot pure water at 60°C, respectively. After solid-liquid separation, it is transferred to an oven and dried at 120°C to obtain the core-shell structured positive electrode precursor with a D50 of 4μm.

[0100] Example 4

[0101] The difference between this embodiment and Embodiment 1 is that the chemical formula of the core-shell structured cathode precursor in this embodiment is Ni. 0.8 Co 0.1 Mn 0.1 (OH)2.

[0102] In the preparation method, the nickel-cobalt-manganese mixed metal sulfate solution is prepared according to the molecular formula Ni 0.8 Co 0.1 Mn 0.1 It is prepared with (OH)2 and the additive is tetramethylammonium hydroxide.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Example 5

[0105] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the volume ratio of nitrogen to air in the first oxidizing atmosphere is 1:0.2.

[0106] The remaining preparation methods and parameters are consistent with those in Example 1.

[0107] Example 6

[0108] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the volume ratio of nitrogen to air in the first oxidizing atmosphere is 1:3.5.

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Example 7

[0111] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the volume ratio of nitrogen to air in the second oxidizing atmosphere is 1:0.25.

[0112] The remaining preparation methods and parameters are consistent with those in Example 1.

[0113] Example 8

[0114] The difference between this embodiment and Embodiment 1 is that in step S1 of this embodiment, the mass fraction of the additive is 15%.

[0115] The remaining preparation methods and parameters are consistent with those in Example 1.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that in the preparation method provided in this comparative example, the entire coprecipitation reaction process is carried out under a nitrogen atmosphere, and no additive solution is added.

[0118] The remaining preparation methods and parameters are consistent with those in Example 1.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 1 is that no additive solution is added in the preparation method provided in this comparative example.

[0121] The remaining preparation methods and parameters are consistent with those in Example 1.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 1 is that in the preparation method provided in this comparative example, the first coprecipitation reaction is carried out under the second oxidizing atmosphere, while the second coprecipitation reaction is carried out under the first oxidizing atmosphere, that is, the order of preparation under the oxidizing atmosphere is adjusted.

[0124] The remaining preparation methods and parameters are consistent with those in Example 1.

[0125] Comparative Example 4

[0126] The difference between this comparative example and Example 1 is that in the preparation method provided in this comparative example, the additive solution is added in the first coprecipitation reaction stage, but not in the second coprecipitation reaction stage.

[0127] The remaining preparation methods and parameters are consistent with those in Example 1.

[0128] Table 1 shows the results of the physicochemical properties of the core-shell structured cathode precursors provided in Examples 1-8 and Comparative Examples 1-4.

[0129] Table 1

[0130]

[0131]

[0132] Single-crystal cathode materials were prepared using the core-shell structured cathode precursors provided in Examples 1-8 and Comparative Examples 1-4.

[0133] Application Example 1

[0134] This application example provides a single-crystal cathode material, and the preparation method of the single-crystal cathode material is as follows:

[0135] The core-shell structured cathode precursor and lithium carbonate powder provided in Example 1 were weighed and mixed evenly according to the molar ratio of Li / Me = 1.10:1, and then subjected to three-stage solid-state sintering in an oxygen atmosphere, namely the first sintering, the second sintering and the third sintering.

[0136] The first sintering process involved heating from room temperature to 500°C at a rate of 4°C / min and holding at that temperature for 6 hours. The second sintering process involved heating from 500°C to 900°C at a rate of 3°C / min and holding at that temperature for 8 hours. The third sintering process involved cooling from 900°C to 780°C at a rate of 3°C / min and holding at that temperature for 8 hours. After sintering, the sample was allowed to cool naturally to room temperature in the furnace. The sample was then pulverized and passed through a 300-mesh sieve to obtain the single-crystal cathode material.

[0137] Application Example 2-8

[0138] The difference between Application Examples 2-8 and Application Example 1 is that the core-shell structured cathode precursors provided in Examples 2-8 are used as the raw materials for preparation.

[0139] The remaining preparation methods and parameters are consistent with those in Application Example 1.

[0140] Application Example 9

[0141] The difference between this application example and application example 1 is that the sintering process in this application example does not include a third sintering process.

[0142] The remaining preparation methods and parameters are consistent with those in Application Example 1.

[0143] Application Example 10

[0144] The difference between this application example and application example 1 is that the third sintering process in this application example is: heating from 900℃ to 1080℃ at a heating rate of 3℃ / min and holding at that temperature for 8 hours.

[0145] The remaining preparation methods and parameters are consistent with those in Application Example 1.

[0146] Compare and contrast examples 1-4

[0147] The difference between Application Examples 1-4 and Application Example 1 is that the core-shell structured cathode precursors provided in Comparative Examples 1-4 are used as raw materials for preparation.

[0148] The remaining preparation methods and parameters are consistent with those in Application Example 1.

[0149] Figure 1 A SEM image of the cross-section of the core-shell structured cathode precursor provided in Example 1 is shown.

[0150] Figure 2 SEM images of the single-crystal cathode material provided in Application Example 1 are shown.

[0151] Figure 3 A SEM image of the cross-section of the core-shell structured cathode precursor provided in Comparative Example 1 is shown.

[0152] Figure 4 SEM images of the single-crystal cathode material provided in Comparative Application Example 1 are shown.

[0153] Figure 5 SEM images of the single-crystal cathode material provided in Comparative Application Example 2 are shown.

[0154] contrast Figure 1 and Figure 3 It can be observed that Comparative Example 1 uses nitrogen protection throughout the coprecipitation reaction and does not add any additives, resulting in precursor particles with high density of primary grains and only a small number of pores, and no ordered arrangement of primary grains in the radial direction; while Example 1 introduces a strong oxidizing atmosphere in the core growth stage of the coprecipitation reaction and a weak oxidizing atmosphere in the shell growth stage, and adds additives, resulting in a special radial structure with high internal porosity and disordered arrangement of primary grains, and low external porosity and oriented arrangement of primary grains.

[0155] contrast Figure 2 , Figure 4 and Figure 5 It can be observed that, under the same sintering process, the cathode material obtained from the precursor system of Example 1 exhibits more pronounced single-crystal characteristics and higher single-crystal particle dispersion; the cathode material obtained from the precursor system of Comparative Example 1 consists of partially agglomerated quasi-single-crystal particles with poor particle dispersion; the cathode material obtained from the precursor system of Comparative Example 2 still shows partially agglomerated quasi-single-crystal particles, and the particle dispersion is still poor, failing to improve the single crystallinity of the cathode material.

[0156] Lithium-ion batteries were prepared using the single-crystal cathode materials provided in Application Examples 1-10 and Comparative Application Examples 1-4:

[0157] Preparation of the positive electrode sheet: A positive electrode slurry was prepared according to the ratio of positive electrode material:SP:PVDF=90:5:5 to obtain a single crystal positive electrode slurry for later use, wherein the solid content of the slurry was 60%; aluminum foil was placed on a coating machine, and a 150μm coating tool was placed on the aluminum foil, the single crystal slurry was poured in, and the equipment was turned on for coating. After coating, an electrode sheet was obtained. The electrode sheet was placed in a 110℃ oven for drying and then rolled to obtain the positive electrode sheet.

[0158] Using a stamping machine in a dry environment, the positive electrode sheets provided in Application Examples 1-10 and Comparative Application Examples 1-4 were cut into circular pieces with a diameter of 15 mm. In a glove box, a lithium metal sheet was used as the counter electrode, and a Ceglard composite membrane was selected as the separator. Electrolyte was added and assembled to obtain a coin cell. The electrolyte was an organic solution obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20. The concentration of lithium salt (lithium hexafluorophosphate) in the electrolyte was 1.15 mol / L.

[0159] The performance of the coin cells provided in Examples 1-9 and Comparative Examples 1-2 was tested using the Wuhan Landian CT2001A system.

[0160] (1) Initial discharge capacity: The voltage range is 2.8 to 4.25V, the charge-discharge rate is 0.2C, and the charge-discharge test is carried out to obtain the initial discharge specific capacity at 0.2C;

[0161] (2) Rate performance: The voltage range is 2.8 to 4.25V, the charging rate is 0.2C, and the discharging rate is 0.2C and 1C. Charge and discharge tests are conducted to obtain the discharge capacity ratio of 1C / 0.2C.

[0162] (3) Cycling performance: The voltage range is 2.8 to 4.25V, the charge and discharge rate is 1C, and the capacity retention rate after 100 cycles is obtained by conducting charge and discharge tests.

[0163] The test results for the above tests are shown in Table 2. Table 2 also shows the Ic of the single-crystal cathode materials provided in Application Examples 1-10 and Comparative Application Examples 1-4. 003 / I 104 The ratio:

[0164] Table 2

[0165]

[0166]

[0167] From Tables 1 and 2, we can obtain:

[0168] The data results from Application Examples 1-4 show that the special core-shell structure of the cathode precursor provided by this invention is beneficial for the removal of impurity ions such as sodium and sulfur during the washing process in the post-processing, further optimizing the quality of the precursor; it can also significantly reduce the sintering temperature when preparing single-crystal cathode materials from the core-shell structure cathode precursor, thereby effectively suppressing the lithium-nickel mixing phenomenon in the cathode material and improving the battery capacity, rate and cycle performance.

[0169] The data from Application Examples 1 and 5-7 show that, during the preparation of the cathode precursor material, by further adjusting the volume ratio of the first oxygen-containing gas to the first non-oxygen gas to (0.3-3):1 and / or the volume ratio of the second oxygen-containing gas to the second non-oxygen gas to (0.02-0.2):1, the pore structure and distribution of the precursor core and shell can be better adjusted, thereby achieving the optimized design of a specific structure precursor and further improving the capacity, rate capability, and cycle performance of the cathode material.

[0170] The data from Application Example 1 and Application Example 8 show that adjusting the mass fraction of the additive to 0.1-10% is more conducive to improving the structural stability of the precursor material, promoting the directional arrangement of the primary grains in the shell, and thus further improving the capacity, rate capability and cycle performance of the cathode material.

[0171] The data results from Application Example 1 and Application Examples 9-10 show that in the process of preparing cathode materials from cathode precursor materials, a three-stage sintering process is carried out, and the sintering process is controlled according to the law of heating-heating-cooling, which is more conducive to the single crystallization of cathode materials, and further improves the capacity, rate capability and cycle performance of cathode materials.

[0172] The data results from Application Example 1 and Comparative Application Examples 1-4 show that in this invention, the order of additive addition and the control of oxygen concentration in the first and second oxidizing atmospheres are indispensable. Without any one of these conditions, the cathode precursor with the special core-shell structure of this invention cannot be obtained, and the impurity content in the cathode precursor cannot be reduced, thus failing to improve the degree of single crystallization of the subsequent cathode material. This results in a significant reduction in the capacity, rate capability, and cycle performance of the cathode material.

[0173] In summary, the core-shell structured cathode precursor provided by this invention features a unique radial structure with high porosity and disordered primary grain arrangement in the core, and low porosity and oriented primary grain arrangement in the outer shell. This results in high tap density, allowing the core to easily shrink during solid-state sintering, thus promoting the breakage of spherical secondary particles and further facilitating the single-crystalization of the cathode material. Furthermore, the radially oriented primary grain arrangement in the outer shell layer is beneficial for mass transfer during sintering. This synergistic effect significantly reduces the sintering temperature when preparing single-crystal cathode materials from the core-shell structured cathode precursor, effectively suppressing lithium-nickel mixing in the cathode material and improving the electrochemical performance of the battery. Moreover, the loose core and radially oriented primary grain arrangement in the outer shell layer facilitate the removal of impurity ions such as sodium and sulfur during post-processing washing, further optimizing the quality of the precursor.

[0174] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A core-shell structured positive electrode precursor, characterized in that, The core-shell structured cathode precursor comprises, from the inside out, a precursor core and a precursor shell layer; the porosity of the precursor core is greater than that of the precursor shell layer, and the primary grains in the precursor shell layer are oriented and distributed along the radial direction of the precursor shell layer. The method for preparing the core-shell structured cathode precursor includes the following steps: A metal mixed salt solution, a precipitant solution, and a complexing agent solution are added in parallel streams, and a first coprecipitation reaction is carried out under a first oxidizing atmosphere to obtain the precursor core. After obtaining the precursor core, an additive solution is added under a second oxidizing atmosphere to carry out a second coprecipitation reaction, thereby obtaining the core-shell structured cathode precursor. Wherein, the oxygen concentration in the first oxidizing atmosphere is greater than the oxygen concentration in the second oxidizing atmosphere; The mass fraction of the additive in the additive solution is 0.1% to 10%. The additives include tetramethylammonium hydroxide and / or triethanolamine.

2. The core-shell structured positive electrode precursor according to claim 1, characterized in that, The median particle size D50 of the core-shell structured cathode precursor is 2~8 μm.

3. The core-shell structured positive electrode precursor according to claim 1, characterized in that, The median particle size D50 of the core-shell structured cathode precursor is 3.5~6 μm.

4. The core-shell structured cathode precursor according to claim 1, characterized in that, The median particle size D50 of the precursor core is 1.5~3μm.

5. A method for preparing a core-shell structured cathode precursor as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: A metal mixed salt solution, a precipitant solution, and a complexing agent solution are added in parallel streams, and a first coprecipitation reaction is carried out under a first oxidizing atmosphere to obtain the precursor core. After obtaining the precursor core, an additive solution is added under a second oxidizing atmosphere to carry out a second coprecipitation reaction, thereby obtaining the core-shell structured cathode precursor. Wherein, the oxygen concentration in the first oxidizing atmosphere is greater than the oxygen concentration in the second oxidizing atmosphere; The mass fraction of the additive in the additive solution is 0.1% to 10%. The additives include tetramethylammonium hydroxide and / or triethanolamine.

6. The preparation method according to claim 5, characterized in that, The metal elements in the mixed salt solution include nickel.

7. The preparation method according to claim 5, characterized in that, The metal elements in the mixed metal salt solution also include element M, which includes transition metal elements.

8. The preparation method according to claim 6, characterized in that, With the total molar amount of all metal elements in the metal mixed salt solution being 100%, the molar amount of nickel is 33% to 98%.

9. The preparation method according to claim 5, characterized in that, The mixed gas in the first oxidizing atmosphere includes a first oxygen-containing gas and a first non-oxygen gas, and the volume ratio of the first oxygen-containing gas to the first non-oxygen gas is (0.3~3):

1.

10. The preparation method according to claim 5, characterized in that, The mixed gas in the second oxidizing atmosphere includes a second oxygen-containing gas and a second non-oxygen gas, and the volume ratio of the second oxygen-containing gas to the second non-oxygen gas is (0.02~0.2):

1.

11. The preparation method according to claim 5, characterized in that, The reaction temperatures of the first coprecipitation reaction and the second coprecipitation reaction are each independently 40~80℃.

12. The preparation method according to claim 5, characterized in that, The rotation speeds of the first coprecipitation reaction and the second coprecipitation reaction are each independently 300~800 rpm.

13. The preparation method according to claim 5, characterized in that, The pH values ​​of the first coprecipitation reaction and the second coprecipitation reaction are each independently 10~11.

14. The preparation method according to claim 5, characterized in that, After the second coprecipitation reaction is completed, washing and drying are performed sequentially.

15. The preparation method according to claim 5, characterized in that, The water content of the core-shell structured cathode precursor is ≤0.8wt%.

16. The preparation method according to claim 5, characterized in that, The preparation method includes the following steps: A metal mixed salt solution, a precipitant solution, and a complexing agent solution are added in parallel streams. A first coprecipitation reaction is carried out under a first oxidizing atmosphere of a mixture of a first oxygen-containing gas and a first non-oxygen gas. The volume ratio of the first oxygen-containing gas to the first non-oxygen gas is (0.3~3):1, and a precursor core is obtained. After obtaining the precursor core, under a second oxidizing atmosphere of a mixture of a second oxygen-containing gas and a second non-oxygen gas, with a volume ratio of the second oxygen-containing gas to the second non-oxygen gas being (0.02~0.2):1, an additive solution with a mass fraction of 0.1~10% is added to carry out a second coprecipitation reaction to obtain the core-shell structured cathode precursor. The metal elements in the mixed metal salt solution include nickel, and the metal elements in the mixed metal salt solution also include element M, which includes transition metal elements; with the total molar amount of all metal elements in the mixed metal salt solution being 100%, the molar amount of nickel accounts for 33% to 98%.

17. A single-crystal cathode material, characterized in that, The single-crystal cathode material is obtained by mixing and sintering a core-shell structured cathode precursor as described in any one of claims 1-4 or a core-shell structured cathode precursor prepared by any one of claims 5-16 with a lithium source.

18. The single-crystal cathode material according to claim 17, characterized in that, The sintering process includes sequentially performing a first sintering, a second sintering, and a third sintering.

19. The single-crystal cathode material according to claim 17, characterized in that, The sintering atmosphere is an oxygen-containing atmosphere.

20. The single-crystal cathode material according to claim 18, characterized in that, The sintering temperature of the first sinter is 400~650℃, and the holding time of the first sinter is 3~10h.

21. The single-crystal cathode material according to claim 18, characterized in that, The sintering temperature of the second sintering is 880~1000℃, and the holding time of the second sintering is 3~12h.

22. The single-crystal cathode material according to claim 18, characterized in that, The holding time for the second sintering is 5-8 hours.

23. The single-crystal cathode material according to claim 18, characterized in that, The sintering temperature of the third sintering is 780~850℃, and the holding time of the third sintering is 3~12h.

24. The single-crystal cathode material according to claim 18, characterized in that, The holding time for the third sintering is 5-8 hours.

25. The single-crystal cathode material according to claim 18, characterized in that, The heating rates of the first sintering and the second sintering are each 1~10℃ / min independently.

26. The single-crystal cathode material according to claim 18, characterized in that, The heating rates of the first sintering and the second sintering are each 2~5℃ / min independently.

27. A battery, characterized in that, The battery comprises the single-crystal cathode material as described in any one of claims 17-26.

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