Nickel-cobalt positive electrode precursor material and preparation method thereof, positive electrode material and battery

Abstract

The invention provides a nickel-cobalt positive electrode precursor material and a preparation method thereof, a positive electrode material and a battery. The preparation method comprises the following steps: adding a nickel-cobalt mixed salt solution, a precipitant solution and a complexing agent solution into a base solution in a parallel flow manner, carrying out a first coprecipitation reaction, and carrying out kettle separation treatment after the reaction is carried out for a first target reaction time; and after the kettle separation treatment, continuously carrying out a second coprecipitation reaction to obtain the nickel-cobalt positive electrode precursor material, wherein in the first coprecipitation reaction process, the stirring rotating speed is increased in an echelon manner; in the second coprecipitation reaction process, the stirring speed is gradually reduced. By regulating and controlling the stirring speed in the coprecipitation reaction process before and after kettle separation, the problems of ball cracking and ball twin of the nickel-cobalt positive electrode precursor material are effectively solved, so that a solid foundation is laid for subsequent preparation of the positive electrode material, and the electrochemical performance of the battery is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a nickel-cobalt positive electrode precursor material and a preparation method thereof, a positive electrode material and a battery. Background Art

[0002] The new energy vehicle industry has experienced rapid development over the past decade. The primary power battery materials used are lithium manganese oxide, ternary lithium, and lithium iron phosphate. However, due to the poor conductivity of lithium iron phosphate, the need for doping with other materials, its low tap density, relatively low specific capacity, strict and specialized manufacturing requirements, and the difficulty of manufacturing, as well as the relatively lagging development of supporting electrolytes, the industrialization of lithium iron phosphate power batteries has been relatively slow, giving rise to the more obvious advantages of ternary cathode materials.

[0003] At present, ternary positive electrode materials include nickel-cobalt-manganese positive electrode materials or nickel-cobalt-aluminum positive electrode materials, and the performance of ternary positive electrode materials mainly depends on the ternary precursor. The requirements of high capacity, high voltage, and excellent cycle performance make nickel-cobalt-aluminum ternary precursors more advantageous than nickel-cobalt-manganese ternary precursors. However, the synthesis process of nickel-cobalt-aluminum ternary precursors is difficult. Aluminum salts require a separate feeding system and cannot be mixed with nickel and cobalt. In addition, ammonia and aluminum ion complexation effects are poor, and controlling the precipitation reaction is extremely difficult. The current method is mainly to synthesize nickel-cobalt binary precursors from nickel and cobalt raw materials.

[0004] In addition, compared with traditional positive electrode materials such as lithium manganese oxide, ternary materials, and lithium iron phosphate, nickel-cobalt binary materials have the advantages of high voltage platform, good safety performance, superior cycle performance and rate performance, and easy high-voltage battery assembly. They have broad application prospects in the field of power batteries.

[0005] In summary, the nickel-cobalt binary precursor material can be used as a precursor for both nickel-cobalt-aluminum cathode materials and nickel-cobalt binary cathode materials, and its preparation process is crucial. The current conventional method for preparing precursors by coprecipitation is generally to prepare a soluble salt of nickel-cobalt metal elements into a mixed solution, and then drip a precipitant therein to obtain an amorphous hydroxide precursor or a carbonate precursor. However, the nickel-cobalt binary precursor synthesized by the traditional coprecipitation process has a wide particle size distribution, the primary particles are relatively thick and large, the secondary particles have obvious ball cracking, the control is unstable, the batch consistency is poor, the tap density is relatively large, the reaction time is limited, and when the particle size grows to a certain range, the ball breaking phenomenon will occur. In addition, during the coprecipitation reaction process, the primary particles are also easy to agglomerate to form twin balls. The above problems seriously affect the preparation of subsequent positive electrode materials, and lead to limited performance of the obtained positive electrode materials.

[0006] Therefore, how to solve the problems of cracked balls and twin balls in the preparation process of nickel-cobalt binary precursor materials is a topic that urgently needs to be explored. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention aims to provide a nickel-cobalt cathode precursor material, a preparation method thereof, a cathode material, and a battery. By regulating the stirring speed during the coprecipitation reaction before and after the separation process, the present invention effectively solves the problems of ball splitting and twinning in the nickel-cobalt cathode precursor material, thereby laying a solid foundation for the subsequent preparation of the cathode material and effectively improving the electrochemical performance of the battery.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing a nickel-cobalt positive electrode precursor material, the preparation method comprising the following steps:

[0010] Adding the nickel-cobalt mixed salt solution, the precipitant solution and the complexing agent solution to the bottom liquid in parallel to carry out a first coprecipitation reaction, and after the reaction reaches a first target reaction time, carrying out a separate still treatment;

[0011] After the split-tank treatment, a second coprecipitation reaction is continued to obtain the nickel-cobalt positive electrode precursor material;

[0012] During the first coprecipitation reaction, the stirring speed is increased step by step; during the second coprecipitation reaction, the stirring speed is decreased step by step.

[0013] It should be noted that the stirring speed in the present invention increases gradually from 130r / min to 160r / min at the initial stage of the reaction (for example, 130r / min, 140r / min, 150r / min or 160r / min, etc.); in addition, the split-still operation described in the present invention specifically refers to transferring half of the material to another still after the split-still requirements are met; and the second coprecipitation reaction is carried out in the newly separated reactor, and the addition of raw materials is consistent with the first coprecipitation reaction stage.

[0014] In the preparation method of the present invention, in the first coprecipitation reaction stage, the stirring speed is increased in a gradient manner. During the particle growth process, the probability of collision between particles is increased, the agglomeration of primary particles is reduced, and the problem of twin balls is avoided. As the stirring speed and reaction time increase, the growth rate of the particles will slow down and the solid content in the reaction system will increase. At this time, in coordination with the second coprecipitation reaction stage, the stirring speed of the reaction is reduced, which suppresses the excessive increase in the tap density of the particles and avoids the occurrence of the problem of particle cracking.

[0015] In the present invention, the gradient increase of the stirring speed in the first coprecipitation reaction process and the gradient decrease of the stirring speed in the second coprecipitation reaction process must be coordinated to jointly solve the problems of splitting and twinning of balls.

[0016] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0017] Preferably, the total metal ion concentration in the nickel-cobalt mixed salt solution is 1.0 mol / L to 2.5 mol / L, for example, 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.3 mol / L or 2.5 mol / L, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0018] The present invention does not specifically limit the molar ratio of nickel and cobalt in the nickel-cobalt mixed salt solution. Those skilled in the art can make adaptive modifications and adjustments based on actual needs. Taking the total molar amount of the nickel and cobalt as 100%, the molar amount of nickel accounts for more than 50% and less than 100%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99%, etc.

[0019] In addition, the salt type in the nickel-cobalt mixed salt solution of the present invention is also a conventional technical solution, and conventional salts that can be used for the preparation of positive electrode precursors are applicable to the present invention, for example, it can be at least one of chloride, sulfate, nitrate or acetate.

[0020] Preferably, the concentration of the precipitant solution is 5 mol / L to 10 mol / L, for example, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L or 10 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, the concentration of the complexing agent solution is 6 mol / L to 12 mol / L, for example, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] It is understandable that the precipitant and complexing agent in the present invention are both types of substances used in the conventional positive electrode precursor preparation stage, and the present invention is applicable to all types of substances that can be reasonably known to those skilled in the art.

[0023] For example, the precipitant includes but is not limited to at least one of sodium hydroxide, potassium hydroxide, sodium carbonate or sodium bicarbonate; the complexing agent includes but is not limited to at least one of ammonia water, citric acid or ethylenediaminetetraacetic acid.

[0024] Preferably, the base liquid comprises a solvent, a complexing agent and a precipitant.

[0025] The base liquid in the present invention is the solution system initially located in the reaction kettle, that is, the startup base liquid.

[0026] Preferably, the concentration of the complexing agent in the base solution is 9 g / L to 10 g / L, for example, 9 g / L, 9.1 g / L, 9.2 g / L, 9.3 g / L, 9.4 g / L, 9.5 g / L, 9.6 g / L, 9.7 g / L, 9.8 g / L, 9.9 g / L or 10 g / L, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0027] Preferably, the pH value of the base solution is 11.0-11.2, such as 11.0, 11.1 or 11.2, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0028] Since cracks may occur due to an increase in the stirring speed during the early first coprecipitation reaction, the present invention appropriately increases the amount of the complexing agent in the base liquid and reduces the pH value of the base liquid. It is particularly preferred that the concentration of the complexing agent in the base liquid is 9-10 g / L and / or the pH value of the base liquid is 11.0-11.2, which appropriately reduces the control reaction time and plays a role in solving the problem of particle cracking in the early stage.

[0029] Preferably, during the first coprecipitation reaction, the increase in the stirring speed is 7 r / h to 15 r / h, for example, 7 r / h, 8 r / h, 9 r / h, 10 r / h, 11 r / h, 12 r / h, 13 r / h, 14 r / h or 15 r / h, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0030] In the present invention, the increase range of the stirring speed is 7 to 15 r / h, which is more conducive to reducing agglomeration and reducing the generation of small particles caused by a sudden increase in the speed.

[0031] Preferably, during the second coprecipitation reaction, the stirring speed is reduced by 5 r / h to 10 r / h, for example, 5 r / h, 6 r / h, 7 r / h, 8 / h, 9 r / h, 10 r / h, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0032] In the present invention, the stirring speed is reduced by 5 to 10 r / h, further reducing the risk of ball cracking caused by continuous high speed.

[0033] Preferably, taking the sum of the reaction times of the first coprecipitation reaction and the second coprecipitation reaction as 100%, the proportion of the first target reaction time is ≤40%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 31%, 32%, 33%, 34%, 35%, 38% or 40%, etc., preferably 30% to 35%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0034] For the technical solution of the present invention, the time for increasing the stirring speed gradient should not be too long. An appropriate first target reaction time is conducive to the uniform growth of particles; further preferably, it is 30% to 35%.

[0035] Preferably, the median particle size D50 of the particles obtained by the first coprecipitation reaction is 6 μm to 7 μm, for example, 6 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm or 7 μm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0036] In addition to regulating the first target reaction time, the present invention further uses the median particle size of the grown particles as the condition for separating the particles, which can ensure the uniform growth of the particles during the entire reaction process.

[0037] Preferably, the reaction temperature of the first coprecipitation reaction and the second coprecipitation reaction is independently 30°C to 80°C, for example, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] Preferably, the pH values ​​of the first coprecipitation reaction and the second coprecipitation reaction are each independently 9.5 to 12, for example, 9.5, 9.8, 10, 10.3, 10.5, 10.8, 11, 11.3, 11.5, 11.81 or 2, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0039] Preferably, the median particle size D50 of the nickel-cobalt positive electrode precursor material is 14μm to 17μm, for example, 14μm, 14.3μm, 14.5μm, 14.8μm, 15μm, 15.3μm, 15.5μm, 15.8μm, 16μm, 16.3μm, 16.5μm, 16.8μm or 17μm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0040] It should also be noted that, in the preparation method provided by the present invention, except for the above-mentioned feature limitations, the rest of the preparation process are conventional technical solutions, and those skilled in the art can make adaptive selections and adjustments based on actual needs.

[0041] Optionally, the solvent in the base liquid is selected from water, and the volume proportion of the base liquid in the reactor is 2 / 3 to 4 / 5.

[0042] Optionally, after the second coprecipitation reaction is completed, the slurry after the reaction is directly washed and dried in sequence without aging treatment.

[0043] In a second aspect, the present invention provides a nickel-cobalt positive electrode precursor material, which is prepared by the preparation method described in the first aspect.

[0044] The nickel-cobalt positive electrode precursor material prepared by the present invention has high sphericity, stable structure, uniform particle size, and no cracked ball or twin ball phenomenon.

[0045] In a third aspect, the present invention provides a positive electrode material, wherein the nickel-cobalt positive electrode material is obtained by mixing and sintering the nickel-cobalt positive electrode precursor material as described in the second aspect with raw materials including a lithium source.

[0046] On the one hand, the nickel-cobalt positive electrode precursor material provided by the present invention can be directly mixed with a lithium source and sintered to obtain a nickel-cobalt binary positive electrode material; on the other hand, an aluminum source can be added at the same time as the lithium source and then sintered to obtain a nickel-cobalt-aluminum ternary positive electrode material; and the preparation details such as the lithium source, aluminum source, mixing method, sintering conditions and specific usage ratio used are all conventional technical solutions, and technical personnel in this field can make adaptive selections and adjustments based on actual needs.

[0047] In a fourth aspect, the present invention further provides a lithium-ion battery, comprising the positive electrode material as described in the third aspect.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] In the preparation method of the present invention, in the first coprecipitation reaction stage, the stirring speed is increased in a gradient manner. During the particle growth process, the probability of collision between particles is increased, the agglomeration of primary particles is reduced, and the problem of twin balls is avoided. As the stirring speed and reaction time increase, the growth rate of the particles will slow down and the solid content in the reaction system will increase. At this time, in coordination with the second coprecipitation reaction stage, the stirring speed of the reaction is reduced, which suppresses the excessive increase in the tap density of the particles and avoids the occurrence of the problem of particle cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1.

[0051] Figure 2 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1.

[0052] Figure 3 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1.

[0053] Figure 4 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1.

[0054] Figure 5 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2.

[0055] Figure 6 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2.

[0056] Figure 7 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2.

[0057] Figure 8 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2.

[0058] Figure 9 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4.

[0059] Figure 10 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4.

[0060] Figure 11 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4.

[0061] Figure 12 This is an SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusions.

[0064] In the description of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0065] Example 1

[0066] This embodiment provides a method for preparing a nickel cobalt hydroxide positive electrode precursor material, and the preparation method is as follows:

[0067] S1: preparing a nickel-cobalt mixed sulfate solution with a molar ratio of nickel to cobalt of 1:1 and a concentration of 2 mol / L, a sodium hydroxide precipitant solution with a concentration of 8 mol / L, and an ammonia complexing agent solution with a concentration of 10 mol / L;

[0068] S2: Add water to the reactor at a volume ratio of 2 / 3, then add ammonia and sodium hydroxide to prepare a reaction base solution with an ammonia concentration of 10 g / L and a pH of 11.0;

[0069] A nickel-cobalt mixed sulfate solution, a sodium hydroxide precipitant solution, and an ammonia complexing agent solution were added to the base liquid in parallel, and a first coprecipitation reaction was started at an initial rotation speed of 130 r / min. During the reaction, the stirring speed was continuously increased by 10 r / h, the reaction temperature was 40° C., and the pH value was 10.8. The first coprecipitation reaction was terminated when the first target reaction time was 33% of the total reaction time, thereby obtaining a first coprecipitation reaction slurry with a particle median particle size D50 of 7 μm.

[0070] S3: The first coprecipitation reaction slurry is separated into separate kettles, and then the nickel-cobalt mixed sulfate solution, the sodium hydroxide precipitant solution, and the ammonia complexing agent solution are added concurrently to the newly separated reactor. The addition conditions are consistent with S1, and a second coprecipitation reaction is performed. During the reaction, the stirring speed is continuously reduced by 7 r / h, the reaction temperature is 40° C., the pH value is 10.8, and the reaction time is 68% of the total reaction time. The second coprecipitation reaction is completed to obtain a second coprecipitation reaction slurry;

[0071] S4: The second coprecipitation reaction slurry is sent to a filter press for washing and then drying to obtain a nickel cobalt hydroxide positive electrode precursor material Ni with a median particle size D50 of 16 μm. 0.5 Co 0.5 (OH)2.

[0072] Example 2

[0073] This embodiment provides a method for preparing a nickel cobalt hydroxide positive electrode precursor material, and the preparation method is as follows:

[0074] S1: preparing a nickel-cobalt mixed sulfate solution with a concentration of 2.5 mol / L and a molar ratio of nickel to cobalt of 1:1, a sodium hydroxide precipitant solution with a concentration of 10 mol / L, and an ammonia complexing agent solution with a concentration of 12 mol / L;

[0075] S2: Add water to the reactor at a volume ratio of 2 / 3, then add ammonia water and sodium hydroxide to prepare a reaction base solution with an ammonia concentration of 9.5 g / L and a pH of 11.1;

[0076] A nickel-cobalt mixed sulfate solution, a sodium hydroxide precipitant solution, and an ammonia complexing agent solution were added to the base liquid in parallel, and a first coprecipitation reaction was started at an initial rotation speed of 140 r / min. During the reaction, the stirring speed was continuously increased by 15 r / h, the reaction temperature was 45° C., and the pH value was 11.0. The first coprecipitation reaction was terminated when the first target reaction time was 30% of the total reaction time, thereby obtaining a first coprecipitation reaction slurry with a particle median particle size D50 of 6 μm.

[0077] S3: The first coprecipitation reaction slurry is separated into separate kettles, and then the nickel-cobalt mixed sulfate solution, the sodium hydroxide precipitant solution, and the ammonia complexing agent solution are added concurrently to the newly separated reactor. The addition conditions are consistent with S1, and a second coprecipitation reaction is performed. During the reaction, the stirring speed is continuously reduced by 10 r / h, the reaction temperature is 45° C., the pH value is 11, and the reaction time is 70% of the total reaction time. The second coprecipitation reaction is completed to obtain a second coprecipitation reaction slurry;

[0078] S4: The second coprecipitation reaction slurry is sent to a filter press for washing and then drying to obtain a nickel cobalt hydroxide positive electrode precursor material Ni with a median particle size D50 of 14 μm. 0.5 Co 0.5 (OH)2.

[0079] Example 3

[0080] This embodiment provides a method for preparing a nickel cobalt hydroxide positive electrode precursor material, and the preparation method is as follows:

[0081] S1: preparing a nickel-cobalt mixed sulfate solution with a concentration of 1.5 mol / L and a molar ratio of nickel to cobalt of 1:1, a sodium hydroxide precipitant solution with a concentration of 5 mol / L, and an ammonia complexing agent solution with a concentration of 6 mol / L;

[0082] S2: Add water in a volume ratio of 7 / 10 to the reactor, then add ammonia water and sodium hydroxide to prepare a reaction base solution with an ammonia concentration of 9 g / L and a pH of 11.2;

[0083] A nickel-cobalt mixed sulfate solution, a sodium hydroxide precipitant solution, and an ammonia complexing agent solution were added to the base liquid in parallel, and a first coprecipitation reaction was started at an initial rotation speed of 160 r / min. During the reaction, the stirring speed was continuously increased by 7 r / h, the reaction temperature was 40° C., and the pH value was 10.8. The first coprecipitation reaction was terminated until the first target reaction time reached 35% of the total reaction time, thereby obtaining a first coprecipitation reaction slurry with a particle median particle size D50 of 6.5 μm.

[0084] S3: The first coprecipitation reaction slurry is separated into separate kettles, and then the nickel-cobalt mixed sulfate solution, the sodium hydroxide precipitant solution, and the ammonia complexing agent solution are added concurrently to the newly separated reactor. The addition conditions are consistent with S1, and a second coprecipitation reaction is performed. During the reaction, the stirring speed is continuously reduced by 5 r / h, the reaction temperature is 40° C., the pH value is 10.8, and the reaction time is 65% of the total reaction time. The second coprecipitation reaction is completed to obtain a second coprecipitation reaction slurry;

[0085] S4: The second coprecipitation reaction slurry is sent to a filter press for washing and then drying to obtain a nickel cobalt hydroxide positive electrode precursor material Ni with a median particle size D50 of 15 μm. 0.5 Co 0.5 (OH)2.

[0086] Example 4

[0087] The difference between this embodiment and embodiment 1 is that in step S1 of this embodiment, a nickel-cobalt mixed sulfate solution with a molar ratio of nickel to cobalt of 85:15 is prepared; and finally a nickel-cobalt hydroxide positive electrode precursor material Ni is obtained. 0.85 Co 0.15 (OH)2.

[0088] The rest of the preparation methods and parameters were the same as those in Example 1.

[0089] Example 5

[0090] The difference between this embodiment and embodiment 1 is that the concentration of ammonia water in the base liquid in step S2 of this embodiment is 8 g / L.

[0091] The rest of the preparation methods and parameters were the same as those in Example 1.

[0092] Example 6

[0093] The difference between this embodiment and embodiment 1 is that the pH value of the base liquid in step S2 of this embodiment is 11.4.

[0094] The rest of the preparation methods and parameters were the same as those in Example 1.

[0095] Example 7

[0096] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the stirring speed is increased by 5 r / h.

[0097] The rest of the preparation methods and parameters were the same as those in Example 1.

[0098] Example 8

[0099] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the stirring speed is increased by 18 r / h.

[0100] The rest of the preparation methods and parameters were the same as those in Example 1.

[0101] Example 9

[0102] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the first target reaction time is 40% of the total reaction time, and the feed flow rate of the raw material is adaptively adjusted to ensure that the D50 value remains unchanged.

[0103] The rest of the preparation methods and parameters were the same as in Example 1.

[0104] Example 10

[0105] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the feed flow rate of the raw materials is regulated to obtain the first coprecipitation reaction slurry with a median particle size D50 of 9 μm.

[0106] The rest of the preparation methods and parameters were the same as those in Example 1.

[0107] Example 11

[0108] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the feed flow rate of the raw materials is regulated to obtain the first coprecipitation reaction slurry with a median particle size D50 of 5 μm.

[0109] The rest of the preparation methods and parameters were the same as those in Example 1.

[0110] Example 12

[0111] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the stirring speed is reduced by 3 r / h.

[0112] The rest of the preparation methods and parameters were the same as those in Example 1.

[0113] Example 13

[0114] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the stirring speed is reduced by 15 r / h.

[0115] The rest of the preparation methods and parameters were the same as those in Example 1.

[0116] Comparative Example 1

[0117] The difference between this comparative example and Example 1 is that this comparative example does not perform the split-tank treatment in step S3, and after the first coprecipitation reaction is completed, the second coprecipitation reaction is directly continued in the original reactor.

[0118] The rest of the preparation methods and parameters were the same as those in Example 1.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 1 is that during the first coprecipitation reaction in step S2 of this comparative example, the stirring speed remains unchanged, and the reaction is directly carried out at the highest stirring speed.

[0121] The rest of the preparation method is consistent with that in Example 1.

[0122] Comparative Example 3

[0123] The difference between this comparative example and Example 1 is that during the second coprecipitation reaction in step S3 of this comparative example, the stirring speed remains unchanged, and the reaction is directly carried out at the lowest stirring speed.

[0124] The rest of the preparation methods and parameters were the same as those in Example 1.

[0125] Comparative Example 4

[0126] The difference between this comparative example and Example 1 is that the change pattern of the stirring speed of the first coprecipitation reaction in step S2 of this comparative example and the change pattern of the stirring speed of the second coprecipitation reaction in step S3 are directly swapped, and the initial speed in step S2 is adjusted to the highest speed during the reaction process.

[0127] The rest of the preparation methods and parameters were the same as those in Example 1.

[0128] The nickel-cobalt positive electrode precursor materials prepared in Examples 1-13 and Comparative Examples 1-4 were tested for particle size, tap density, and specific surface area, and the microscopic morphology of the particles was characterized to determine whether they had ball cracking and twinning problems.

[0129] Particle size: Laser particle size analyzer is used for particle size testing.

[0130] Specific surface area: nitrogen adsorption method.

[0131] Tap density: tested using a tap density meter.

[0132] Particle micromorphology: scanning electron microscopy (SEM).

[0133] Figure 1 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1 is shown.

[0134] Figure 2 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1 is shown.

[0135] Figure 3 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1 is shown.

[0136] Figure 4 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Example 1 is shown.

[0137] Figure 5 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2 is shown.

[0138] Figure 6 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2 is shown.

[0139] Figure 7 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2 is shown.

[0140] Figure 8 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 2 is shown.

[0141] Figure 9 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4 is shown.

[0142] Figure 10 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4 is shown.

[0143] Figure 11 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4 is shown.

[0144] Figure 12 The SEM image of the nickel cobalt hydroxide positive electrode precursor material provided in Comparative Example 4 is shown.

[0145] from Figures 1 to 4 It can be seen that the nickel-cobalt hydroxide binary precursor material obtained by the preparation method provided by the present invention has good particle size uniformity and no twinning or splitting phenomena occur.

[0146] from Figures 5 to 8 It can be seen that the nickel-cobalt hydroxide binary precursor material obtained by the preparation method of Comparative Example 2 has obvious twin-sphere phenomenon, and some particles also have split-sphere phenomenon.

[0147] from Figures 9 to 12 It can be seen that the nickel-cobalt hydroxide binary precursor material obtained in Comparative Example 4 not only has obvious ball splitting phenomenon, the particle cracks are very obvious, but also has obvious twin ball phenomenon.

[0148] The test results of the above tests are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152] Note: The standard for slight is that under the same magnification, less than one-fifth of the particles in the SEM image have twinning or splitting phenomenon; while the standard in the table is that more than one-fifth of the particles have twinning or splitting phenomenon.

[0153] In summary, in the preparation method of the present invention, in the first coprecipitation reaction stage, the stirring speed is increased gradually. During the particle growth process, the collision probability between particles is increased, the agglomeration of primary particles is reduced, and the problem of twin balls is avoided. As the stirring speed and reaction time increase, the growth rate of the particles will slow down and the solid content in the reaction system will increase. At this time, in coordination with the second coprecipitation reaction stage, the stirring speed of the reaction is reduced to suppress the transient increase of the particle tap density, thereby avoiding the occurrence of the particle cracking problem.

[0154] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a nickel-cobalt cathode precursor material, characterized in that: The preparation method comprises the following steps: Adding the nickel-cobalt mixed salt solution, the precipitant solution and the complexing agent solution to the bottom liquid in parallel to carry out a first coprecipitation reaction, and after the reaction reaches a first target reaction time, carrying out a separate still treatment; After the split-tank treatment, a second coprecipitation reaction is continued to obtain the nickel-cobalt positive electrode precursor material; During the first coprecipitation reaction, the stirring speed is increased step by step; during the second coprecipitation reaction, the stirring speed is decreased step by step.

2. The preparation method according to claim 1, characterized in that The total metal ion concentration in the nickel-cobalt mixed salt solution is 1.0 mol / L to 2.5 mol / L; Preferably, the concentration of the precipitant solution is 5 mol / L to 10 mol / L; Preferably, the concentration of the complexing agent solution is 6 mol / L to 12 mol / L.

3. The preparation method according to claim 1, characterized in that The base liquid includes a solvent, a complexing agent and a precipitant; Preferably, the concentration of the complexing agent in the base solution is 9 g / L to 10 g / L, and the pH value of the base solution is 11.0 to 11.

2.

4. The preparation method according to claim 1 or 3, characterized in that During the first coprecipitation reaction, the stirring speed is increased by 7 r / h to 15 r / h.

5. The preparation method according to claim 1, characterized in that During the second coprecipitation reaction, the stirring speed is reduced by 5 r / h to 10 r / h.

6. The preparation method according to claim 1, characterized in that Taking the sum of the reaction times of the first coprecipitation reaction and the second coprecipitation reaction as 100%, the proportion of the first target reaction time is ≤40%, preferably 30% to 35%.

7. The preparation method according to claim 1 or 6, characterized in that The median particle size D50 of the particles obtained by the first coprecipitation reaction is 6 μm to 7 μm; Preferably, the reaction temperature of the first coprecipitation reaction and the second coprecipitation reaction are each independently 30°C to 80°C; Preferably, the pH values ​​of the first coprecipitation reaction and the second coprecipitation reaction are each independently 9.5 to 12; Preferably, the median particle size D50 of the nickel-cobalt positive electrode precursor material is 14 μm to 17 μm.

8. A nickel-cobalt cathode precursor material, characterized in that: The nickel-cobalt positive electrode precursor material is prepared by the preparation method according to any one of claims 1 to 7.

9. A positive electrode material, characterized in that The nickel-cobalt positive electrode material is obtained by mixing and sintering the nickel-cobalt positive electrode precursor material as claimed in claim 8 with raw materials including a lithium source.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to claim 9.

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