Ternary positive electrode material, preparation method thereof and lithium battery

Abstract

The invention discloses a ternary positive electrode material, a preparation method thereof and a lithium battery, and relates to the technical field of positive electrode materials. The polycrystalline ternary positive electrode material is a secondary particle formed by assembling a plurality of primary particles, so that the size of the primary particles is # imgabs 0 #, the arrangement angle is theta, the void ratio is epsilon, and the distribution proportion of the large and small particles in the ternary positive electrode material is # imgabs 1 #; and the method has obvious influence on internal stress accumulation and yield limit of secondary particles caused by anisotropic volume shrinkage and expansion in the charging and discharging process of the primary particles. The product parameters are mutually coordinated and influenced, the ternary positive electrode material is constructed by utilizing the parameters to form an expression of a stability parameter F, and the F is enabled to meet a specific range, so that the stability of the ternary positive electrode material structure can be improved, stress fatigue can be coped with, generation of microcracks can be reduced, and improvement of the cycle performance of a battery is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and in particular to a ternary positive electrode material and a preparation method thereof, and a lithium battery. Background Art

[0002] Ternary cathode material LiNi x Co y Mn z O2 (x ≥ 0.6) has the advantages of high capacity, low cost and large-scale production, and is one of the best materials for high-energy-density lithium battery positive electrodes. During the cycle process, polycrystalline ternary positive electrode materials will cause fracture of polycrystalline positive electrode materials under the action of electrochemical-mechanical coupling, among which fracture at the grain boundary is the most common. Cracks are generated because the stress accumulation exceeds the yield limit of the particles, and cracks are generated between the grain boundaries; during the cycle process, the cracks gradually extend from the inside of the secondary particles to the surface, and even pulverize the particles.

[0003] Among them, the microcracks of the ternary cathode material provide channels for the electrolyte to penetrate into the secondary particles, intensifying the side reactions between the material and the electrolyte, making the highly active Ni 4+ The reaction generates the rock salt phase of NiO, which not only consumes the electrolyte and active materials, but also forms an area of ​​electron and ion isolation inside the particles, increasing the resistance of the material and accelerating the decline in capacity during the cycle process. In addition, the anisotropic volume shrinkage and expansion of the primary particles during the charge and discharge process has a huge impact on the internal stress accumulation and yield limit of the secondary particles.

[0004] Therefore, there is an urgent need to provide a ternary positive electrode material that can cope with stress fatigue in order to reduce the generation of microcracks and improve the cycle performance of the battery.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a ternary positive electrode material and a preparation method thereof and a lithium battery, aiming to reduce the generation of microcracks in the positive electrode material and improve the cycle performance of the battery.

[0007] The present invention is achieved in that: In a first aspect, the present invention provides a ternary positive electrode material, which satisfies: F= ; 0.5°≤F≤40°; Wherein, F represents the stability parameter of the ternary cathode material, and the unit is °; It represents the maximum Feret diameter of the primary particle section corresponding to the primary particle section in the secondary particle section of the ternary positive electrode material, in μm; It represents the minimum circumscribed circle diameter of the secondary particle section corresponding to the primary particle, in μm; It represents the angle between the radial radius of the minimum circumscribed circle of the secondary particle section passing through the midpoint of the maximum Feret diameter of the primary particle section and the maximum Feret diameter of the primary particle in the direction with a shorter distance to the minimum circumscribed circle, in degrees; represents the void ratio, , represents the true density, represents the compacted density, and The unit is g / cm 3 ; and They represent the particle sizes corresponding to the cumulative volume of 90% and 10% of the corresponding batches of ternary cathode material particles, respectively. is the particle size corresponding to the maximum y value in the particle size distribution diagram, , , The unit is μm; n represents the number of primary particles selected from the same secondary particle or different secondary particles, n≥40.

[0008] In an optional embodiment, the ternary positive electrode material satisfies at least one of the following characteristics A1-K1: Feature A1: 0.1 ≤ ≤1.0; Feature B1: 0°≤ ≤70°; Feature C1: 0.5°≤ ≤20°; Feature D1: 0.5 ≤ ≤20; Feature E1: 0.1 ≤ ≤6.5; Feature F1: ≤5μm, 2μm≤ ≤25μm, 0.05≤ ≤0.5; Feature G1: 0°≤ ≤110°; Characteristic H1: 0.1 ≤ ≤0.4; Feature I1: 3μm≤ ≤15μm, 6μm≤ ≤25μm, 2μm≤ ≤8μm; Feature J1: 4.4 g / cm 3 ≤ ≤5.1g / cm 3 , and 3.15g / cm 3 ≤ ≤3.85g / cm 3 ; Feature K1: The selection of n primary particles must meet the following conditions: <0.1 and 0.1≤ , and select The number of primary particles <0.1 is 0.1≤ Corresponding to 2.5-3.5 times the number of particles at one time.

[0009] In a second aspect, the present invention further provides a method for preparing a ternary positive electrode material, comprising: using a cobalt source, a nickel source and a manganese source to perform a coprecipitation reaction to obtain a precursor intermediate; The precursor intermediate is adjusted to a pH value of 8-9, then mixed with a guide agent for reaction, and then mixed with an initiator for reaction, and then the pH value is increased to continue coprecipitation reaction using a cobalt source, a nickel source, and a manganese source, and solid-liquid separation is performed to obtain a precursor; The precursor is mixed with a lithium source and calcined.

[0010] In an optional embodiment, the process of preparing a precursor using a precursor intermediate satisfies at least one of the following features A2-E2: Feature A2: The directing agent is at least one selected from the group consisting of allyl phosphate monoammonium salt, vinyl phosphate, cis-allyl phosphate and allyl phosphate; Feature B2: The concentration of the guiding agent is controlled to be 0.7 mol / L-1.0 mol / L; Characteristic C2: The reaction temperature with the directing agent is 15°C-35°C, and the reaction time is 1.5h-2.5h; Feature D2: During the reaction with the initiator and the initiator, ultrasonic oscillation is performed, and the frequency of the ultrasonic oscillation is 15kHz-30kHz; Feature E2: The pH value of the precursor intermediate is adjusted to 8-9 using an acid solution, and the acid solution is selected from at least one of a sulfuric acid solution, an acetic acid solution and a citric acid solution.

[0011] In an optional embodiment, the process of preparing a precursor using a precursor intermediate satisfies at least one of the following features A3-D3: Feature A3: The initiator is at least one selected from 2,2-azobis(2-methylpropylimidamide) dihydrochloride and azobisisobutylamidine hydrochloride; Feature B3: Control the added concentration of the initiator to be 4 g / L-6 g / L; Characteristic C3: The reaction temperature with the initiator is 15°C-35°C, and the reaction time is 1.5h-2.5h; Feature D3: After the reaction with the initiator is completed, the pH value is raised to 11.0-11.5, and a nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution are introduced for a coprecipitation reaction for 6h-20h. After solid-liquid separation, washing and drying, a precursor is obtained.

[0012] In an optional embodiment, the process of preparing the precursor intermediate comprises: introducing a nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution into a reaction kettle with a base liquid, and stirring the reaction for 2h-3h; wherein the nickel-cobalt-manganese mixed salt solution is obtained by mixing a nickel source, a cobalt source and a manganese source, and the molar ratio of the nickel element, the cobalt element and the manganese element is 5:2:3, 1:1:1, 4:2:4, 6:2:2, 8:1:1 or (86-96):(2-9):(2-5); And / or, during the preparation of the precursor intermediate, the reaction temperature is controlled to be 45° C.-60° C. and the stirring rate is controlled to be 400 rpm-700 rpm.

[0013] In an optional embodiment, the process for preparing the precursor intermediate satisfies at least one of the following features A4-C4: Feature A4: The concentration of the nickel-cobalt-manganese mixed salt solution is 1.5 mol / L-2.2 mol / L, and the feed rate is 25 mL / min-35 mL / min; Feature B4: The precipitant solution is a sodium hydroxide solution with a concentration of 10 mol / L-12 mol / L, and the pH value of the solution in the reactor is maintained at 11.0-11.5 by adjusting the introduction rate of the sodium hydroxide solution; Characteristic C4: The complexing agent solution is an ammonia solution, and the ammonia concentration in the solution in the reactor is adjusted to be 0.7 mol / L-1.1 mol / L by adjusting the introduction rate of the ammonia solution. In an optional embodiment, the precursor is mixed with a lithium source and then calcined in two steps to obtain a ternary cathode material intermediate; The ternary cathode material intermediate is mixed with the coating agent and calcined.

[0014] In an optional embodiment, the process of preparing the ternary cathode material using the precursor satisfies at least one of the following characteristics A5-G5: Feature A5: Two-step calcination includes: first, keeping the temperature at 400°C-550°C for 3h-5h, then heating to 750°C-800°C and keeping the temperature for 12h-15h; Feature B5: The molar ratio of lithium to the total amount of nickel, cobalt and manganese is controlled to be (1.03-1.07): 1; Characteristic C5: Precursor and lithium source are mixed, ground and then calcined in two steps; Feature D5: The lithium source is selected from at least one of lithium hydroxide, lithium carbonate and lithium oxalate; Feature E5: The coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3 and MgF2; Feature F5: The mass ratio of the coating agent to the ternary cathode material intermediate is (5-10): 100; Feature G5: The calcination temperature of the ternary positive electrode material intermediate and the coating agent is 550℃-650℃, and the calcination time is 3h-8h.

[0015] In a third aspect, the present invention further provides a lithium battery, comprising the ternary positive electrode material provided in any of the above embodiments or the ternary positive electrode material prepared by the preparation method provided in any of the above embodiments.

[0016] The present invention has the following beneficial effects: Since the polycrystalline ternary positive electrode material is assembled from a plurality of primary particles to obtain secondary particles, the size of the primary particles is , arrangement angle θ, porosity ε, and distribution ratio of large and small particles in the ternary cathode material , which has a significant impact on the internal stress accumulation and yield limit of secondary particles caused by the anisotropic volume shrinkage and expansion of primary particles during charge and discharge. The above product parameters have a coordinated influence on each other. By using the above parameters to construct the expression of the stability parameter F of the ternary positive electrode material, and making F meet a specific range, the stability of the ternary positive electrode material structure can be improved, stress fatigue can be dealt with, the generation of microcracks can be reduced, and the cycle performance of the battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a SEM cross-sectional view of secondary particles of the ternary positive electrode material provided in Example 1 of the present invention; Figure 2 This is a SEM cross-sectional view of the secondary particles of the ternary positive electrode material provided in Comparative Example 1 of the present invention; Figure 3 The primary particles, secondary particles, and d R ,d r and Schematic diagram of . DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0020] In order to better evaluate the performance of ternary positive electrode materials in dealing with stress fatigue and provide ternary positive electrode materials with high cycle performance and low capacity decay rate, the present invention comprehensively considers the size of primary particles. , arrangement angle θ, porosity ε, and distribution ratio of large and small particles in the ternary cathode material The expression of the stability parameter F of the ternary positive electrode material is constructed by adjusting the structure of the ternary positive electrode material and adjusting its value range.

[0021] The expression for the stability parameter F of the ternary cathode material is as follows: F= ; The ternary positive electrode material provided in an embodiment of the present invention satisfies: 0.5°≤F≤40°, such as 0.5°, 1.0°, 3.0°, 5.0°, 8.0°, 10.0°, 13.0°, 15.0°, 18.0°, 20.0°, 23.0°, 25.0°, 28.0°, 30.0°, 33.0°, 35.0°, 38.0°, 40.0°, etc., and the unit of F is °.

[0022] The parameters in the expression of the stability parameter F of the ternary positive electrode material are explained as follows: It indicates the maximum Feret diameter (hereinafter referred to as diameter) of the primary particle section corresponding to the section of the secondary particle section in the ternary positive electrode material, in μm; It indicates the minimum circumscribed circle diameter (hereinafter referred to as diameter) of the cross section of the secondary particle corresponding to the primary particle, in μm. It represents the size of the primary particle relative to the secondary particle. The larger the value is, the greater the influence of the stress accumulation of the primary particle on the secondary particle.

[0023] It represents the angle between the radial radius of the minimum circumscribed circle of the secondary particle section passing through the midpoint of the maximum Feret diameter of the primary particle section and the maximum Feret diameter of the primary particle in the direction with a shorter distance to the minimum circumscribed circle, in degrees. It indicates the deviation angle of the radial arrangement of primary particles in secondary particles. The larger the deviation angle, the more unfavorable it is for stress relief, which will lead to stress concentration.

[0024] Specifically, , and , obtained by analyzing the cross-section scanning electron microscope (SEM) image of the positive electrode material using ImageJ. For the specific test process, please refer to the specific embodiment below.

[0025] Indicates the porosity. The larger the value, the more gaps there are between the particles, which can relieve the stress. However, if the value is too large, there will be too many gaps, which is not conducive to the stability of the secondary particle structure. , represents the true density, represents the compacted density, and The unit is g / cm 3 , the void ratio can be calculated by testing the true density and compacted density .

[0026] and They represent the particle sizes corresponding to the cumulative volume of 90% and 10% of the corresponding batches of ternary cathode material particles, respectively. is the particle size corresponding to the maximum y value in the particle size distribution diagram, , , The unit is μm. , , Obtained by laser particle size analyzer, It refers to the particle size corresponding to the maximum y value on the normal distribution particle size distribution curve. Its specific value is generally less than . It represents the distribution ratio of large particles and small particles on both sides of the particle size Dvmax in the particle size distribution diagram. The larger the secondary particles are, the easier it is to produce concentrated stress, and the easier it is to exceed the yield limit and cause rupture.

[0027] n represents the number of primary particles selected from the same secondary particle or different secondary particles, n≥40, such as 40, 60, 80, 100, 120, 150, 180, 200, etc., and the number can also be more to improve the accuracy of detection. In a preferred embodiment, the selection of n primary particles must meet the following conditions: <0.1 and 0.1≤ , and select The number of primary particles <0.1 is 0.1≤ Corresponding to 2.5-3.5 times the number of primary particles (such as 2.5 times, 2.8 times, 3.0 times, 3.2 times, 3.5 times, etc.).

[0028] It should be noted that since the polycrystalline ternary cathode material is assembled from multiple primary particles to obtain secondary particles, the size of the primary particles is , arrangement angle θ, porosity ε, and distribution ratio of large and small particles in the ternary cathode material , which has a significant impact on the internal stress accumulation and yield limit of the secondary particles caused by the anisotropic volume shrinkage and expansion of the primary particles during the charge and discharge process. At the same time, the above product parameters have a coordinated influence on each other. Particles, if If the If it is small, it is relatively conducive to stress relief; The smaller the value, the less conducive it is to stress relief. The larger the value, the better it is for stress relief. However, too large a value will cause capacity loss and be detrimental to the stability of the structure. It reflects the proportion of large and small particles in the secondary particles. The larger the value, the more large particles there are in the secondary particles, and the easier they are to break. Within the specified range, the structural stability of the ternary positive electrode material is better.

[0029] In some embodiments, it is preferable that each parameter in the expression of the stability parameter F of the ternary positive electrode material is controlled within a certain range: 0.1≤ ≤1.0, Indicates all selected particles The average value of The value can be 0.1, 0.3, 0.5, 0.8, 1.0, etc. If the value of is too large, the stress accumulation of the primary particles will have too great an impact on the secondary particles, which is not conducive to obtaining a ternary positive electrode material that can cope with stress fatigue.

[0030] 0°≤ ≤70°, Indicates all selected particles The average value of can be 0°, 5°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, etc.

[0031] 0.5°≤ ≤20°, The value of within this range is more conducive to stress relief. The specific values ​​can be 0.5°, 1.0°, 3.0°, 5.0°, 8.0°, 10.0°, 13.0°, 15.0°, 18.0°, 20.0°, etc.

[0032] 0.5≤ ≤20, It can reflect the proportion of large and small particles in the secondary particles. If the value is too large, it is easy to break. The value can be 0.5, 1.0, 3.0, 5.0, 8.0, 10.0, 13.0, 15.0, 18.0, 20.0, etc.

[0033] 0.1≤ ≤6.5, If the value of is too large, it will affect the stability of the structure, and if it is too small, it will not be conducive to stress relief. The value of can be 0.10, 0.50, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00, 6.50, etc.

[0034] ≤5μm, 2μm≤ ≤25μm, 0.05≤ ≤0.5. , , The value of within the above range is more conducive to stress relief. Specifically, The value of can be 0.1μm, 0.5μm, 1.0μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, etc.; The value of can be 2μm, 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, 20μm, 23μm, 25μm, etc.; The value of can be 0.05, 0.08, 0.10, 0.20, 0.30, 0.40, 0.50, etc.

[0035] 0°≤ ≤110°, A value that is too large is not conducive to stress relief. The specific value can be 0°, 5°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, etc.

[0036] 0.1≤ ≤0.4, If the value is too large, it will cause capacity loss and is not conducive to the stability of the structure. If the value is too small, it will not be conducive to stress release. The value can be 0.1, 0.2, 0.3, 0.4, etc.

[0037] 3μm≤ ≤15μm, 6μm≤ ≤25μm, 2μm≤ ≤8μm. , , The value of is within the above range, which is more conducive to stress release. Specifically, The value of can be 3μm, 5μm, 8μm, 10μm, 13μm, 15μm, etc.; The value of can be 6μm, 10μm, 15μm, 20μm, 25μm, etc.; The value of can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, etc.

[0038] 4.4g / cm 3 ≤ ≤5.1g / cm 3 , and 3.15g / cm 3 ≤ ≤3.85g / cm 3 . , The value of within the above range can make The value is more appropriate, which is conducive to stress release and will not affect the structural stability. The value can be 4.4g / cm 3 , 4.5g / cm 3 , 4.6g / cm 3 , 4.7g / cm 3 , 4.8g / cm 3 , 4.9g / cm 3 , 5.0g / cm 3 , 5.1g / cm 3 wait; The value can be 3.15g / cm 3 、3.20g / cm 3 、3.30g / cm 3 , 3.40g / cm 3 、3.50g / cm 3 、3.60g / cm 3 、3.70g / cm 3 、3.80g / cm 3 、3.85g / cm 3 wait.

[0039] The present invention also provides a method for preparing a ternary positive electrode material, the steps of which are as follows: S1. Preparation of precursor intermediates A coprecipitation reaction is carried out using a cobalt source, a nickel source and a manganese source in the presence of a precipitant and a complexing agent to obtain a precursor intermediate in the form of a slurry. In the actual operation process, a nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution are introduced into a reactor with a bottom liquid, and the reaction is stirred for 2h-3h (such as 2.0h, 2.5h, 3.0h, etc.), and the feeding of the three solutions is stopped.

[0040] In some embodiments, the nickel-cobalt-manganese mixed salt solution is obtained by mixing a nickel source, a cobalt source, a manganese source and a solvent, and the molar ratio of nickel element, cobalt element and manganese element is 5:2:3, 1:1:1, 4:2:4, 6:2:2, 8:1:1 or (86-96):(2-9):(2-5), and the molar ratio of nickel-cobalt-manganese can be any one of the above, such as 5:2:3, 1:1:1, 4:2:4, 6:2:2, 8:1:1, 86:9:5, 88:8:4, 90:7:3, 92:5:3, 96:2:2, etc. The type of solvent is not limited, such as water; the cobalt source is at least one of cobalt sulfate and its hydrate, the nickel source is at least one of nickel sulfate and its hydrate, and the manganese source is at least one of manganese sulfate and its hydrate. The concentration of the nickel-cobalt-manganese mixed salt solution is 1.5mol / L-2.2mol / L, such as 1.5mol / L, 1.8mol / L, 2.0mol / L, 2.2mol / L, etc. The feed rate is 25mL / min-35mL / min, such as 25mL / min, 28mL / min, 30mL / min, 32mL / min, 35mL / min, etc. By adjusting the concentration and feed rate of the nickel-cobalt-manganese mixed salt solution, it is more appropriate to adjust the growth rate of the solid particles and improve the uniformity of the product.

[0041] In some embodiments, the precipitant solution can be a sodium hydroxide solution, and the concentration of the sodium hydroxide solution can be 10mol / L-12mol / L, such as 10mol / L, 11mol / L, 12mol / L, etc. By adjusting the rate of passage of the sodium hydroxide solution, the pH value of the solution in the reactor is maintained at 11.0-11.5, such as 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, etc. The complexing agent solution can be an ammonia solution, and the ammonia concentration in the solution in the reactor is 0.7mol / L-1.1mol / L by adjusting the rate of passage of the ammonia solution, such as 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, etc. By regulating the pH value and ammonia concentration of the solution in the reactor, it is more appropriate to regulate the precipitation rate to meet the requirements of the coprecipitation reaction. In some embodiments, during the preparation of the precursor intermediate, the reaction temperature is controlled to be 45°C-60°C, such as 45°C, 50°C, 55°C, 60°C, etc.; the stirring rate is 400rpm-700rpm, such as 400rpm, 500rpm, 600rpm, 700rpm, etc.

[0042] It should be noted that the concentration of ammonia water, reaction pH value, feed rate and stirring speed have an impact on the looseness of secondary particles, and the size of secondary particles and primary particles. Therefore, the particle size distribution of the material, its looseness and the size of primary particles can be controlled by adjusting the reaction parameters.

[0043] S2. Preparation of precursor The precursor intermediate obtained in step S1 is adjusted to a pH value of 8-9, then mixed with a guide agent for reaction, and then mixed with an initiator for reaction, and then the pH value is increased to continue the coprecipitation reaction using a cobalt source, a nickel source, and a manganese source, and solid-liquid separation is performed to obtain a precursor. By adding a guide agent and an initiator, the grain arrangement can be regulated, the orderly arrangement can be increased, and the size of the primary particles can be more controllable.

[0044] In some embodiments, the inducing agent is selected from at least one of allyl phosphate monoammonium salt, vinyl phosphate (VPA), cis-allyl phosphate (cPPA) and allyl phosphate (APA), and the inducing agent can be any one or more of the above. The concentration of the inducing agent added is controlled to be 0.7mol / L-1.0mol / L, such as 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, etc. The reaction temperature with the inducing agent is 15°C-35°C, such as 15°C, 20°C, 25°C, 30°C, 35°C, etc.; the reaction time with the inducing agent is 1.5h-2.5h, such as 1.5h, 1.8h, 2.0h, 2.3h, 2.5h, etc.

[0045] In some embodiments, the initiator is selected from at least one of 2,2-azobis(2-methylpropylimidamide) dihydrochloride and azobisisobutylamidine hydrochloride (V-50), and the initiator can be any one or more of the above. The added concentration of the initiator is controlled to be 4g / L-6g / L, such as 4.0g / L, 4.5g / L, 5.0g / L, 5.5g / L, 6.0g / L, etc. The reaction temperature with the initiator is 15°C-35°C, such as 15°C, 20°C, 25°C, 30°C, 35°C, etc.; the reaction time is 1.5h-2.5h, such as 1.5h, 1.8h, 2.0h, 2.3h, 2.5h, etc.

[0046] It should be noted that during the precursor precipitation process, the unsaturated transition metal atoms exposed on the (010) crystal plane of the precursor particles can have a strong coordination effect with the phosphoric acid groups of the directing agent to form an insoluble soap adsorbed on the crystal plane. In addition, the outward double bonds in the directing agent will undergo a polymerization reaction with the outward double bonds in the directing agent on the (010) crystal plane in the free crystal grains under the action of the initiator, guiding the crystal grains to be arranged in an orderly manner and reducing the angle at which the primary particles deviate from the radial direction of the minimum circumscribed circle of the secondary particles in the secondary particles. Due to the addition of the directing agent, the adsorption of the metal amine complex ion on the (010) crystal plane is hindered, the growth trend of the

[010] crystal direction is reduced, and the growth of the grains in the

[001] direction is promoted. At the same time, this process increases the orderly arrangement of the grains.

[0047] In some embodiments, ultrasonic oscillation is performed during the reaction with the inducing agent and the initiating agent, and the frequency of the ultrasonic oscillation is 15kHz-30kHz, such as 15kHz, 20kHz, 25kHz, 30kHz, etc. Ultrasonic oscillation is performed during the reaction with the inducing agent and the initiating agent, which, on the one hand, loosens the crystal grains inside the secondary particles and adjusts the order of the primary particles; on the other hand, increases the exposed area of ​​the (010) crystal plane, and increases the number of primary particles with orderly arrangement and controllable size.

[0048] In some embodiments, the pH value of the precursor intermediate is adjusted to 8-9 by an acid solution, such as 8.0, 8.3, 8.5, 8.7, 9.0, etc. The acid solution is selected from at least one of a sulfuric acid solution, an acetic acid solution and a citric acid solution, and the acid solution can be any one or more of the above.

[0049] In some embodiments, after the reaction with the initiator is completed, the pH value is raised to 11.0-11.5 (such as 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, etc.) using sodium hydroxide solution, and a nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution are introduced for a coprecipitation reaction for 6h-20h (such as 6h, 8h, 10h, 13h, 15h, 18h, 20h, etc.). Afterwards, the precursor is obtained by solid-liquid separation, washing, and drying. The method of solid-liquid separation is not limited, and it can be filtering or the like; washing can be done by water washing, and the number of water washings is not limited.

[0050] S3. Calcination The precursor is mixed with a lithium source and calcined to obtain a ternary positive electrode material.

[0051] In order to improve the electrochemical properties of the ternary positive electrode material, the calcination process was optimized: after the precursor was mixed with the lithium source, it was calcined in two steps to obtain the ternary positive electrode material intermediate; then, the ternary positive electrode material intermediate was mixed with the coating agent and calcined.

[0052] In some embodiments, the two-step calcination includes: first keeping the temperature at 400°C-550°C for 3h-5h, then heating to 750°C-800°C for 12h-15h, and the heating rate of the two-step calcination can be 2°C / min-4°C / min. Specifically, the calcination temperature of the first step calcination can be 400°C, 450°C, 500°C, 550°C, etc., and the holding time can be 3h, 4h, 5h, etc.; the calcination temperature of the second step calcination can be 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, etc., and the holding time can be 12h, 13h, 14h, 15h, etc. The calcination atmosphere can be air or oxygen.

[0053] Furthermore, when adding materials, the molar ratio of lithium to the total amount of nickel, cobalt and manganese is controlled to be (1.03-1.07):1, such as 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, etc. The precursor and the lithium source that meet the ratio requirements are mixed, ground and then calcined in two steps to improve the uniformity of the positive electrode material product. The lithium source is selected from at least one of lithium hydroxide, lithium carbonate and lithium oxalate, and the lithium source can be any one or more of the above.

[0054] In some embodiments, the coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3 and MgF2, and the coating agent can be any one or more of the above. By coating the surface of the positive electrode material and introducing the above doping elements, it is beneficial to improve the cycle stability of the positive electrode material. The mass ratio of the coating agent to the ternary positive electrode material intermediate is (5-10): 100, such as 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, etc.

[0055] Furthermore, the calcination temperature of the ternary positive electrode material intermediate and the coating agent is 550℃-650℃, such as 550℃, 580℃, 600℃, 630℃, 650℃, etc.; the calcination time is 3h-8h, such as 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0056] An embodiment of the present invention also provides a lithium battery, including the ternary positive electrode material provided by the embodiment of the present invention. Since the ternary positive electrode material with an F value within the specified range has better structural stability, it is beneficial to improve the cycle stability of the lithium battery.

[0057] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0058] The embodiment of the present invention provides a ternary positive electrode material as shown in Table 1. The ternary positive electrode materials in the embodiment and comparative example in Table 1 are tested, and the specific items and methods are as follows: (1) Particle size distribution: According to GB / T 19077-2016, the particle size distribution information of the ternary cathode material provided in each embodiment and comparative example was measured using a laser particle size analyzer.

[0059] (2) Morphology characterization: The cross-section of the ternary cathode material provided in each embodiment and comparative example was tested using a scanning electron microscope. Figure 1 This is a SEM image of the cross section of the ternary cathode material provided in Example 1. Figure 2 The SEM image of the cross section of the ternary cathode material provided for Comparative Example 1 is as follows: Figure 1 The primary particles are arranged in a more orderly manner.

[0060] (3) Test method for the angle of deviation of primary particles from the minimum circumscribed circle radius of secondary particles (for details, refer to Figure 3 ): 1) obtain an SEM image of the cross-section of the ternary positive electrode material that can be analyzed; 2) use the tools in ImageJ to find the maximum Feret's diameter of the secondary particle cross-section, and observe the point C on the secondary particle cross-section that is the longest perpendicular to the Feret's diameter. The two ends of the Feret's diameter are point A and point B respectively. Draw a circle with points A, B and C to obtain the minimum circumscribed circle of the corresponding secondary particle cross-section of the ternary positive electrode material, and obtain the center of the corresponding minimum circumscribed circle; 3) use the tools in ImageJ to identify the boundaries of the primary particles in the SEM image, and independently select the area of ​​each primary particle in the SEM image; 4) use ImageJ analysis to obtain the maximum Feret's diameter of each primary particle area and the minimum circumscribed circle diameter of the secondary particles. It is also possible to obtain the angle between the radial radius of the secondary particle minimum circumscribed circle passing through the midpoint of the maximum Feret's diameter of the primary particle cross-section in the cross-section and the maximum Feret's diameter in the direction with a shorter distance from the primary particle to the minimum circumscribed circle. .

[0061] (4) Compacted density test: According to GB / T 24533-2009, the ternary positive electrode materials provided in each embodiment and comparative example were tested using a compacted density meter. The test results of each embodiment and comparative example are shown in Table 1.

[0062] (5) True density test: According to GB / T 24586-2009, the ternary positive electrode materials provided in each embodiment and comparative example were tested using a Bester physical adsorption instrument-TD. The test results of each embodiment and comparative example are shown in Table 1.

[0063] (6) Electrochemical performance test: Battery preparation method: The prepared positive electrode material, acetylene black and PVDF were weighed in a mass ratio of 90:5:5, and the above three substances were added into NMP solvent and stirred and mixed thoroughly. The slurry was made after ultrasonic dispersion, and the slurry was evenly coated on aluminum foil, and then transferred to a 120°C vacuum oven for drying. After 12 h, the dried electrode was taken out and rolled, and then punched to obtain a circular positive electrode with a diameter of 14 mm; a metal lithium sheet was used as the negative electrode, and 1 mol·L -1 LiPF6 organic solution (EC:DEC:DMC=1:1:1, volume ratio) was used as the electrolyte, Celgrd2400 polypropylene microporous membrane was used as the separator, and button cells were assembled in a glove box protected by high-purity argon. After the battery was assembled, it was left to stand for 4 hours, and then the electrical performance was tested using the LAND battery test system.

[0064] Electrochemical performance test: The positive electrode materials provided in the embodiment and the comparative example were made into button batteries, and the discharge specific capacities of 0.1C, 1C, 2C and 5C were tested at 25°C; the capacity retention rates of 100 and 300 cycles were tested at room temperature. The cycle performance test conditions were: using a LAND charge and discharge instrument, the voltage range was 3.0-4.3V (622\523) and 2.8~4.30V (811), and the results are shown in Table 2.

[0065] It should be noted that 50 primary particles are selected, and the selection of 50 primary particles must meet the following conditions: <0.1 and 0.1≤ , and select The number of primary particles <0.1 is 0.1≤ Corresponding to 2.5-3.5 times the number of particles at one time.

[0066] The mean of the parameters is also calculated from 50 particles.

[0067] Table 1 Parameters of ternary positive electrode materials provided in various embodiments and comparative examples

[0068] Table 2 Electrochemical properties of ternary cathode materials provided in various embodiments and comparative examples

[0069] Different particle size ratios of primary particles to corresponding secondary particles and different offset angles of primary particles can be used to obtain different Different true density (ρ) and compacted density (CD) give different void fractions (ε); further, different , size distribution and porosity, and different F are obtained. The ternary positive electrode materials in the range of 0.5°≤F≤40° have good rate performance and cycle performance.

[0070] Among them, the relative size of the primary particle and the corresponding secondary particle, as well as the angle of the primary particle from the minimum circumscribed circle radius of the secondary particle, reflect the arrangement order of the secondary particles formed by the accumulation of the primary particles, corresponding to The value of reflects the quality of its arrangement order. Specifically, The smaller the ratio is, the smaller the influence of θ on the overall arrangement order of secondary particles is. The smaller the value, the better the arrangement order. Therefore, the corresponding relationship between the primary particles and the secondary particles in the ternary positive electrode material is expressed by the formula It means that the smaller the value is, the higher the ranking is.

[0071] True density (ρ) and compacted density (CD) are used to obtain different porosities (ε), which reflect the porosity of the entire positive electrode material. If the porosity is too low, it is not conducive to the stress release of particle shrinkage and expansion during the charge and discharge process of the positive electrode material; while if the porosity is too high, the capacity density of the material will be low. Compared with Example 1, the ternary positive electrode materials provided in Examples 7-8 have different porosities, corresponding to different F values, and corresponding to different rate performance and cycle performance of the positive electrode materials.

[0072] The highest volume distribution in the particle size distribution diagram corresponds to the proportion of particles of different particle sizes on both sides of the particle size distribution, which affects the proportion of particles of different sizes in the positive electrode material. The larger the value, the higher the proportion of large particles, and the lower the cycle performance of the positive electrode material; the smaller the value, the higher the proportion of small particles, and the better the cycle performance of the positive electrode material. Compared with Example 1, Examples 9-10 correspond to different , corresponding to different F values, the rate performance and cycle performance of the positive electrode material are different.

[0073] The preparation methods of the above embodiments and comparative examples are described below.

[0074] Example 1 (1) Preparation of precursor intermediates: Nickel sulfate, cobalt sulfate and manganese sulfate were mixed and dissolved in water at a molar ratio of 8:1:1 to obtain a metal salt solution, which was added to the bottom liquid at a certain rate, and a 10 mol / L NaOH solution was added at a certain rate to maintain the pH value of the solution in the reactor at 11.3. Nitrogen was introduced at the same time, and a 2 mol / L NH3·H2O solution was added at a certain rate. The reaction was stirred for 2.5 hours to obtain a precursor intermediate, and the addition was stopped. Among them, the concentration of the metal salt solution was 2 mol / L, the feed rate was 30 mL / min; the reaction process temperature was 55 ° C, the stirring rate was 500 rpm; the concentration of NH3·H2O solution in the reactor was 0.9 mol / L. The bottom liquid was obtained by mixing sodium hydroxide solution, NH3·H2O solution and water, the pH value of the bottom liquid was 11.3, and the ammonia concentration of the bottom liquid was 0.1 mol / L (i.e., the concentration of ammonia).

[0075] (2) Preparation of precursor: After adding sulfuric acid solution to the reactor to adjust the pH of the solution in the reactor to 8.5, ultrasonic oscillation was used and allyl phosphate monoammonium salt was added, the temperature was lowered to 25°C and the reaction was continued for 2 hours, 2,2-azobis(2-methylpropylimidamide) dihydrochloride was added, the reaction was continued at 25°C for 2 hours, the temperature was raised to the original reaction temperature of step (1), NaOH solution was added and the pH of the solution in the reactor was maintained at 11.3, the metal salt solution and NH3·H2O solution were continued to be added, the reaction was continued for 15 hours, and the precursor was obtained by filtering, washing and drying. The concentration of allyl phosphate monoammonium salt in the solution in the reactor was 0.85 mol / L; the concentration of 2,2-azobis(2-methylpropylimidamide) dihydrochloride in the solution in the reactor was 5 g / L; and the frequency of ultrasonic oscillation was 25 kHz.

[0076] (3) Preparation of ternary cathode materials: The precursor and lithium carbonate are mixed in a molar ratio of Li:(Ni+Co+Mn) of 1.05:1, and then ground and calcined in two steps, wherein the calcination atmosphere is oxygen. The two-step calcination includes a first calcination process in which the temperature is raised to 480°C, kept warm for 4 hours, and then continued to rise to 750°C and kept warm for 15 hours to obtain a ternary positive electrode material intermediate, wherein the heating rate is 3°C / min.

[0077] The coating agent TiO2 and the ternary cathode material intermediate were mixed in a mass ratio of 6:100 and calcined at 600°C for 6h to obtain the ternary cathode material.

[0078] The preparation method settings of each embodiment and comparative example (the conditions not listed in the following table are the same as those of embodiment 1): (1) Preparation of precursor intermediates: Table 3 Parameter settings for preparing precursor intermediates in various embodiments and comparative examples

[0079] (2) Preparation of precursor: Table 4 Parameter settings for preparing precursors in various embodiments and comparative examples

[0080] (3) Preparation of ternary cathode materials: Table 5 Parameter settings for preparing ternary positive electrode materials in various embodiments and comparative examples

[0081] It can be seen that by introducing the initiator and the initiator reaction, and cooperating with the ultrasonic treatment, the value of F can be controlled within the range defined by the present invention, which is beneficial to improving the electrochemical performance of the material. This may be because the above means affect the ordering of the grains, can increase the orderly arrangement, and make the size of the primary particles more controllable.

[0082] It can be seen from Tables 1 to 5 that for materials of the same type with a nickel-cobalt-manganese molar ratio (such as Examples 1 to 10), as the F value increases within the specified range, the cycle performance gradually decreases.

[0083] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A ternary positive electrode material, characterized in that: The ternary cathode material meets the following requirements: F= ； 0.5°≤F≤40°； Wherein, F represents the stability parameter of the ternary cathode material, and the unit is °; It represents the maximum Feret diameter of the primary particle section corresponding to the primary particle section in the secondary particle section of the ternary positive electrode material, in μm; It represents the minimum circumscribed circle diameter of the secondary particle section corresponding to the primary particle, in μm; It represents the angle between the radial radius of the minimum circumscribed circle of the secondary particle section passing through the midpoint of the maximum Feret diameter of the primary particle section and the maximum Feret diameter of the primary particle in the direction with a shorter distance to the minimum circumscribed circle, in degrees; represents the void ratio, , represents the true density, represents the compacted density, and The unit is g / cm 3 ; and They represent the particle sizes corresponding to the cumulative volume of 90% and 10% of the corresponding batches of ternary cathode material particles, respectively. is the particle size corresponding to the maximum y value in the particle size distribution diagram, , , The unit is μm; n represents the number of primary particles selected from the same secondary particle or different secondary particles, n≥40.

2. The ternary positive electrode material according to claim 1, characterized in that: The ternary positive electrode material satisfies at least one of the following characteristics A1-K1: Feature A1: 0.1 ≤ ≤1.0; feature B1：0°≤ ≤70°； Feature C1: 0.5°≤ ≤20°; Feature D1: 0.5 ≤ ≤20; feature E1：0.1≤ ≤6.5； Feature F1: ≤5μm, 2μm≤ ≤25μm, 0.05≤ ≤0.5; Feature G1: 0°≤ ≤110°; Characteristic H1: 0.1 ≤ ≤0.4; Feature I1: 3μm≤ ≤15μm, 6μm≤ ≤25μm, 2μm≤ ≤8μm; Feature J1: 4.4 g / cm 3 ≤ ≤5.1g / cm 3 , and 3.15g / cm 3 ≤ ≤3.85g / cm 3 ; Feature K1: where n The selection of primary particles must meet the following conditions: <0.1 and 0.1≤ , and select The number of primary particles <0.1 is 0.1≤ Corresponding to 2.5-3.5 times the number of particles at one time.

3. A method for preparing the ternary positive electrode material according to any one of claims 1 to 2, characterized in that: include: A coprecipitation reaction is carried out using a cobalt source, a nickel source and a manganese source to obtain a precursor intermediate; The precursor intermediate is adjusted to a pH value of 8-9, then mixed with a directing agent for reaction, and then mixed with an initiator for reaction, and then the pH value is increased to continue coprecipitation reaction using a cobalt source, a nickel source and a manganese source, and solid-liquid separation is performed to obtain a precursor; The precursor is mixed with a lithium source and calcined.

4. The preparation method according to claim 3, characterized in that: The process of preparing the precursor using the precursor intermediate satisfies at least one of the following features A2-E2: Feature A2: The directing agent is selected from at least one of allyl phosphate monoammonium salt, vinyl phosphate, cis-allyl phosphate and allyl phosphate; Feature B2: The concentration of the guiding agent is controlled to be 0.7 mol / L-1.0 mol / L; Characteristic C2: The reaction temperature with the directing agent is 15°C-35°C, and the reaction time is 1.5h-2.5h; Feature D2: During the reaction with the inducing agent and the initiator, ultrasonic oscillation is performed, and the frequency of the ultrasonic oscillation is 15kHz-30kHz; Feature E2: The pH value of the precursor intermediate is adjusted to 8-9 using an acid solution, and the acid solution is selected from at least one of a sulfuric acid solution, an acetic acid solution and a citric acid solution.

5. The preparation method according to claim 3 or 4, characterized in that: The process of preparing the precursor using the precursor intermediate satisfies at least one of the following features A3-D3: Feature A3: The initiator is selected from at least one of 2,2-azobis(2-methylpropylimidamide) dihydrochloride and azobisisobutylamidine hydrochloride; Feature B3: The added concentration of the initiator is controlled to be 4 g / L-6 g / L; feature C3: The reaction temperature with the initiator is 15°C-35°C, and the reaction time is 1.5h-2.5h; Feature D3: After the reaction with the initiator is completed, the pH value is raised to 11.0-11.5, and a nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution are introduced for a coprecipitation reaction for 6h-20h. After solid-liquid separation, washing and drying, a precursor is obtained.

6. The preparation method according to claim 3, characterized in that: The process of preparing the precursor intermediate comprises: introducing a nickel-cobalt-manganese mixed salt solution, a precipitant solution and a complexing agent solution into a reaction kettle with a base liquid, and stirring the reaction for 2h-3h; wherein the nickel-cobalt-manganese mixed salt solution is obtained by mixing the nickel source, the cobalt source and the manganese source, and the molar ratio of the nickel element, the cobalt element and the manganese element is 5:2:3, 1:1:1, 4:2:4, 6:2:2, 8:1:1 or (86-96):(2-9):(2-5); And / or, during the preparation of the precursor intermediate, the reaction temperature is controlled to be 45° C.-60° C. and the stirring rate is controlled to be 400 rpm-700 rpm.

7. The preparation method according to claim 6, characterized in that: The process for preparing the precursor intermediate satisfies at least one of the following features A4-C4: Feature A4: The concentration of the nickel-cobalt-manganese mixed salt solution is 1.5 mol / L-2.2 mol / L, and the feed rate is 25 mL / min-35 mL / min; Feature B4: The precipitant solution is a sodium hydroxide solution with a concentration of 10 mol / L-12 mol / L, and the pH value of the solution in the reactor is maintained at 11.0-11.5 by adjusting the introduction rate of the sodium hydroxide solution; Characteristic C4: The complexing agent solution is an ammonia solution, and the ammonia concentration in the solution in the reactor is adjusted to be 0.7 mol / L-1.1 mol / L by adjusting the introduction rate of the ammonia solution.

8. The preparation method according to claim 3, characterized in that: After mixing the precursor with the lithium source, calcining in two steps to obtain a ternary positive electrode material intermediate; The ternary cathode material intermediate is mixed with a coating agent and calcined.

9. The preparation method according to claim 8, characterized in that: The process of preparing the ternary cathode material using the precursor satisfies at least one of the following features A5-G5: Feature A5: The two-step calcination comprises: firstly keeping the temperature at 400°C-550°C for 3h-5h, then heating to 750°C-800°C and keeping the temperature for 12h-15h; Feature B5: The molar ratio of lithium to the total amount of nickel, cobalt and manganese is controlled to be (1.03-1.07): 1; Characteristic C5: the precursor and the lithium source are mixed, ground and then calcined in two steps; Feature D5: The lithium source is selected from at least one of lithium hydroxide, lithium carbonate and lithium oxalate; Feature E5: The coating agent is selected from at least one of V2O5, Al2O3, ZrO2, TiO2, SnO2, ZnO, MgO, RuO2, La2O3, CeO2, Co3O4, SiO2, FePO4, Li3PO4, Li2MnO3, LiAlO2, Li2TiO3, Li2ZrO3, Li3VO4, Li2SiO3, AlF3, LaF3 and MgF2; Feature F5: The mass ratio of the coating agent to the ternary cathode material intermediate is (5-10): 100; Feature G5: The calcination temperature of the ternary positive electrode material intermediate and the coating agent is 550°C-650°C, and the calcination time is 3h-8h.

10. A lithium battery, characterized in that: It includes the ternary positive electrode material described in any one of claims 1-2 or the ternary positive electrode material prepared by the preparation method described in any one of claims 3-9.

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