Spherical nickel hydroxide and preparation method and application thereof

Abstract

The invention provides spherical nickel hydroxide as well as a preparation method and application thereof, and relates to the technical field of lithium ion battery precursors. The spherical nickel hydroxide comprises secondary particles; the secondary particles are formed by stacking primary particles on the surface of the crystal nucleus, the primary particles are spindle-shaped, the average length of the primary particles is 600-900 nm, and the average width of the primary particles is 150-250 nm. By limiting the morphology and size of the primary particles, both the energy density and the lithium ion transmission efficiency can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery precursors, and in particular relates to spherical nickel hydroxide and a preparation method and application thereof. Background Art

[0002] With the development of modern energy technology, lithium-ion batteries are widely used in digital, transportation, communications and other fields. Among them, positive electrode materials are an important component of lithium-ion batteries, and the electrochemical properties of positive electrode materials and their precursors are the decisive factors affecting battery performance. As the requirements for battery performance become higher and higher, higher requirements are also placed on the energy density and rate performance of positive electrode materials and their precursors.

[0003] At present, the precursors of positive electrode materials for ternary lithium-ion batteries, nickel-based batteries and other batteries are mostly nickel hydroxide. Nickel hydroxide can be divided into ordinary nickel hydroxide and spherical nickel hydroxide according to its morphology. Among them, spherical nickel hydroxide has a higher packing density than ordinary nickel hydroxide. The positive electrode material made of spherical nickel hydroxide can improve the packing density and mechanical stability. At present, spherical nickel hydroxide is mostly prepared by intermittent or continuous processes. Although the internal stacking of the nickel hydroxide currently prepared is denser and more compact, which can improve the energy density, the lithium ion transmission path is not smooth, resulting in poor lithium ion transmission efficiency, which is not conducive to improving the rate performance.

[0004] Therefore, how to provide a spherical nickel hydroxide that improves both energy density and lithium ion transmission efficiency is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] The main purpose of the present invention is to provide a spherical nickel hydroxide and a preparation method and application thereof, so as to solve the technical problem in the prior art that it is difficult to improve both energy density and lithium ion transmission efficiency, so that the positive electrode material prepared therefrom has excellent energy density and rate performance.

[0006] In order to achieve the above-mentioned purpose, according to the first aspect of the present invention, a spherical nickel hydroxide is provided, which includes secondary particles; the secondary particles are formed by stacking primary particles on the surface of the crystal nucleus, wherein the primary particles are spindle-shaped, and the average length of the primary particles is 600-900nm, and the average width is 150-250nm.

[0007] Further, the particle size distribution width SPAN of the spherical nickel hydroxide is 0.5 to 0.6; and / or the median particle size D50 of the spherical nickel hydroxide is 3.0 to 5.0 μm; and / or the tap density of the spherical nickel hydroxide is 1.9 to 2.2 g / cm 3 ; and / or, the specific surface area of ​​the spherical nickel hydroxide is 6 to 13 m 2 / g; and / or, the length direction of the primary particles deviates from the direction perpendicular to the radial direction of the secondary particles by 0 to 30°.

[0008] According to a second aspect of the present invention, there is provided a method for preparing the spherical nickel hydroxide provided in the first aspect, comprising the following steps: pumping a nickel salt solution, an alkali solution and an ammonia solution into a reaction kettle and mixing them to form a reaction slurry, causing the reaction slurry to undergo a coprecipitation reaction to obtain spherical nickel hydroxide; wherein the coprecipitation reaction comprises a first stage and a second stage; in the first stage, the pH value of the reaction slurry is A1, and the ammonia value is B1; in the second stage, the pH value of the reaction slurry is A2, and the ammonia value is B2, satisfying: A1>A2, B1<B2.

[0009] Furthermore, at 45°C, A1 is 11.50-12.30; and / or, B1 is 0-5 g / L; and / or, at 45°C, A2 is 10.80-11.90; and / or, B2 is 2-8 g / L; and / or, the temperature of the coprecipitation reaction is 45-55°C, and the time of the first stage does not exceed 6 hours.

[0010] Furthermore, in the first stage, the stirring speed in the reactor is controlled to be C1; in the second stage, when the product particle size D50 in the reactor reaches 50% to 80% of the target particle size, the stirring speed in the reactor is controlled to be C2; ​​when the product particle size D50 in the reactor reaches more than 80% of the target particle size, the stirring speed in the reactor is controlled to be C3, satisfying C1>C2>C3; preferably, C1 is 400 to 500 rpm; and / or, C2 is 350 to 450 rpm; and / or, C3 is 250 to 350 rpm.

[0011] Furthermore, in the first stage, the feed flow rate of the nickel salt solution pumped into the reactor is D1; ​​in the second stage, the feed flow rate of the nickel salt solution pumped into the reactor is D2, satisfying D1≤D2; preferably, D1 is 6-20 L / h; and / or, D2 is 30-60 L / h.

[0012] Furthermore, before the nickel salt solution, alkali solution and ammonia water are pumped into the reactor, the following steps are also included: adding water as the base liquid into the reactor, controlling the stirring speed in the reactor to C1 and the temperature to 45-55°C, and then adding alkali solution and ammonia water to adjust the pH value of the base liquid to A1 and the ammonia value to B1; preferably, at 45°C, A1 is 11.50-12.30; and / or B1 is 0-5g / L; and / or C1 is 400-500rpm.

[0013] Furthermore, the reaction device used includes a reactor and a concentrator; wherein the reactor is used to accommodate the reaction slurry and provide the reaction slurry for co-precipitation reaction therein; the concentrator is used to receive part of the reaction slurry overflowing from the reactor and provide the reaction slurry for suction filtration and concentration treatment therein; in the second stage, the following steps are also included: when the liquid level of the reactor reaches the overflow liquid level, the reaction slurry overflows into the concentrator; when the liquid level of the concentrator reaches the preset liquid level, the reaction slurry overflowing into the concentrator is subjected to suction filtration and concentration treatment, and then returned to the reactor; preferably, the overflow liquid level refers to the liquid level in the reactor reaching 60-70% of the height of the inner cavity of the reactor, and the preset liquid level refers to the liquid level in the concentrator reaching 40-80% of the height of the inner cavity of the concentrator, and the stirring speed of the concentrator during the suction filtration and concentration treatment is 250-350rpm.

[0014] Furthermore, after the coprecipitation reaction, washing treatment and drying treatment are also included; wherein the washing treatment includes alkali washing treatment and water washing treatment; preferably, the washing liquid used for the alkali washing treatment is a sodium hydroxide solution with a temperature of 50 to 80°C and a concentration of 1 to 4 mol / L; preferably, the temperature of the water used for the water washing treatment is 40 to 80°C; preferably, the temperature of the drying treatment is 80 to 160°C, and the water is dried to ≤0.2wt%.

[0015] Furthermore, the molar concentration of nickel ions in the nickel salt solution is 1.5 to 3.0 mol / L; and / or, the nickel salt in the nickel salt solution includes nickel sulfate; and / or, the alkaline substance in the alkali solution includes sodium hydroxide; and / or, the molar concentration of the alkaline substance in the alkali solution is 5.0 to 10.0 mol / L; and / or, the concentration of NH3 in the ammonia water is 3.0 to 6.0 mol / L.

[0016] According to a third aspect of the present invention, there is provided a positive electrode material, which is prepared by sintering raw materials including nickel hydroxide, wherein the nickel hydroxide includes the spherical nickel hydroxide provided by the first aspect or the spherical nickel hydroxide prepared by the preparation method provided by the second aspect.

[0017] The implementation of the present invention has at least the following beneficial effects:

[0018] The spherical nickel hydroxide provided by the present invention, by limiting the morphology and size of the primary particles, has spindle-shaped primary particles tightly stacked, without losing a high tap density, the specific surface area of ​​the spherical nickel hydroxide is increased, and when the positive electrode material is prepared by subsequent lithium sintering, the lithium uniformity is better, and it is also helpful to increase the specific surface area of ​​the positive electrode material, so that the active sites involved in the electrochemical reaction are increased, thereby taking into account the improvement of energy density and lithium ion transmission efficiency; in addition, the primary particles with this specific structure and size have a short lithium ion diffusion path, and can be quickly deintercalated during charging and discharging, which helps to further improve the lithium ion transmission efficiency. Therefore, the spherical nickel hydroxide provided by the present invention can take into account the improvement of energy density and lithium ion transmission efficiency, so that the positive electrode material formed by the spherical nickel hydroxide has excellent specific capacity and rate performance when applied to batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0020] Figure 1 A schematic diagram of the structure of a reaction device according to one embodiment of the present invention;

[0021] Figure 2 This is a 3000x SEM image of the spherical nickel hydroxide prepared in Example 1 of the present invention;

[0022] Figure 3 This is a 10,000-fold SEM image of the spherical nickel hydroxide prepared in Example 1 of the present invention;

[0023] Figure 4 This is a 20,000-fold SEM image of a cross section of the spherical nickel hydroxide prepared in Example 1 of the present invention;

[0024] Figure 5 This is a 3000-fold SEM image of the spherical nickel hydroxide prepared in Comparative Example 1 of the present invention;

[0025] Figure 6 This is a 10,000-fold SEM image of the spherical nickel hydroxide prepared in Comparative Example 1 of the present invention;

[0026] Figure 7 This is a 20,000-fold SEM image of a cross section of the spherical nickel hydroxide prepared in Comparative Example 1 of the present invention.

[0027] Description of reference numerals:

[0028] 1-reactor; 2-concentrator; 3-circulation reflux pump; 101-input unit; 102-first stirring unit; 103-second stirring unit; 104-overflow pipe; 105-reflux pipe; 106-concentrator feed valve; 201-filter rod assembly. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0030] As described in the background technology, it is difficult to improve both the energy density and lithium ion transmission efficiency of the positive electrode material in the prior art. In order to solve the above technical problems, the first aspect of the present invention provides a spherical nickel hydroxide, which includes secondary particles; the secondary particles are formed by stacking primary particles on the surface of the crystal core, wherein the primary particles are spindle-shaped, and the average length of the primary particles is 600-900nm, and the average width is 150-250nm.

[0031] Spherical nickel hydroxide is composed of a plurality of secondary particles, and the secondary particles have a spherical or quasi-spherical structure. Specifically, it can be a porous secondary particle formed by the growth of primary particles on the surface of the crystal nucleus, wherein the primary particles can be stacked continuously from the surface of the crystal nucleus to the outer surface of the secondary particles, and it can also be understood that the interior of the secondary particle is the crystal nucleus, and the primary particles are stacked around the crystal nucleus. By limiting the morphology and size of the primary particles, a channel for rapid migration of lithium ions can be provided, the lithium ion diffusion path is short, and rapid deintercalation can be achieved during charge and discharge, which helps to improve the lithium ion transmission efficiency. In addition, it also helps to form a structure in which the primary particles are stacked radially.

[0032] Among them, the primary particles have a spindle-shaped structure and are tightly stacked. Without losing the higher tap density, the specific surface area of ​​the spherical nickel hydroxide can be increased. In the subsequent lithiation sintering to prepare the positive electrode material, the lithiation uniformity is better, and it is also helpful to increase the specific surface area of ​​the positive electrode material, so that the active sites involved in the electrochemical reaction are increased, which helps to improve the energy density and lithium ion transmission efficiency, thereby helping to improve the specific capacity and rate performance of the battery formed by the positive electrode material.

[0033] The spherical nickel hydroxide of the present invention may be β-Ni(OH)2, and the present invention does not make too many limitations here.

[0034] In some embodiments, the particle size distribution width SPAN of the spherical nickel hydroxide is 0.5 to 0.6, for example, 0.5, 0.51, 0.52, 0.53, 0.55, 0.58, 0.6 or a range composed of any two thereof. By limiting the particle size distribution width SPAN of the spherical nickel hydroxide to a suitable range, the particle size distribution width is more concentrated, which is conducive to improving the tap density of the spherical nickel hydroxide, and can provide a certain mechanical strength and a higher energy density for the subsequently prepared positive electrode material.

[0035] Specifically, the particle size distribution width of spherical nickel hydroxide substantially refers to the particle size distribution width of all secondary particles in spherical nickel hydroxide. The particle size distribution width of spherical nickel hydroxide is calculated according to the formula (D90-D10) / D50, where D10 is the particle size corresponding to 10% of the volume cumulative distribution percentage of the sample, D50 is the particle size corresponding to 50% of the volume cumulative distribution percentage of the sample, and D90 is the particle size corresponding to 90% of the volume cumulative distribution percentage of the sample.

[0036] The present invention does not limit the test method of D10, D50 and D90 of the spherical nickel hydroxide, and for example, a laser particle size analyzer may be used for measurement.

[0037] The present invention does not limit the specific values ​​of D10, D50, and D90. For example, in some embodiments, the median particle size D50 of spherical nickel hydroxide is 3.0-5.0 μm, D10 is 2-4 μm, D90 is 5-6 μm, and the maximum particle size Dmax is 7-8 μm, wherein Dmax refers to the largest particle size in the particle distribution. By limiting the particle size to meet the above requirements, the particle size distribution width SPAN of spherical nickel hydroxide can be 0.5-0.6, the mechanical strength and compaction density can be improved, and the particles can be prevented from cracking during stress and circulation.

[0038] In some embodiments, the tap density of the spherical nickel hydroxide is 1.9 to 2.2 g / cm 3 , for example 1.9 g / cm 3 , 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 Or a range consisting of any two of them. The tap density refers to the mass per unit volume of the powder in the container after being tapped under specified conditions. By limiting the tap density of the spherical nickel hydroxide to the above range, the compaction density when it is subsequently formed into a positive electrode material can be further ensured, thereby helping to improve the energy density of the positive electrode material.

[0039] In some embodiments, the specific surface area of ​​the spherical nickel hydroxide is 6 to 13 m 2 / g, for example 6m2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g or any two thereof. By limiting the specific surface area of ​​the spherical nickel hydroxide within the above range, it is ensured that when the positive electrode material is prepared by subsequent lithium sintering, the lithium uniformity is better, the specific surface area of ​​the positive electrode material is increased, and the active sites participating in the electrochemical reaction are increased, which helps to improve the energy density and lithium ion transmission efficiency, thereby helping to improve the specific capacity and rate performance of the battery formed by the positive electrode material.

[0040] In some embodiments, the length direction of the primary particle deviates from the direction perpendicular to the radial direction of the secondary particle by 0 to 30 degrees. It can also be understood that the primary particles are arranged along the radial direction of the secondary particles. By limiting the morphology and stacking structure of the primary particles, when spherical nickel hydroxide is used for lithium sintering to prepare the positive electrode material, the positive electrode material can inherit the stacking structure of its primary particles. This structure can significantly reduce the inter-granular stress of the positive electrode material and inhibit the pulverization of the secondary particles. In addition, this structure provides a channel for rapid migration of lithium ions, the lithium ion diffusion path is short, and it can be quickly deintercalated during charging and discharging, which helps to improve the lithium ion transmission efficiency.

[0041] The second aspect of the present invention provides a method for preparing the spherical nickel hydroxide provided in the first aspect, comprising the following steps: pumping a nickel salt solution, an alkali solution and an ammonia solution into a reaction kettle and mixing them to form a reaction slurry, causing the reaction slurry to undergo a coprecipitation reaction to obtain spherical nickel hydroxide; wherein the coprecipitation reaction includes a first stage and a second stage; in the first stage, the pH value of the reaction slurry is A1, and the ammonia value is B1; in the second stage, the pH value of the reaction slurry is A2, and the ammonia value is B2, satisfying: A1>A2, B1<B2.

[0042] The crystallization process of crystalline materials is divided into two stages: nucleation and nuclear growth. Specifically, a crystal nucleus is first formed in the reaction solution, and then spherical nickel hydroxide with a specific size grows on the basis of the crystal nucleus. The process of forming the crystal nucleus is the nucleation stage, and the process of forming spherical nickel hydroxide with a specific size is the nuclear growth stage.

[0043] In the present invention, a nickel salt solution, an alkali solution and an ammonia solution undergo a coprecipitation reaction in a reactor, wherein the alkali solution serves as a precipitant and the ammonia solution serves as a complexing agent, and the coprecipitation reaction includes a first stage and a second stage. The first stage can be understood as a nucleation stage, and the second stage can be understood as a growth stage.

[0044] The present invention defines A1>A2, B1<B2, that is, nucleation is performed under relatively high pH, ​​low ammonia or no ammonia conditions, and growth is performed under relatively low pH, medium ammonia conditions. Such nucleation conditions can effectively ensure the dispersion of the crystal nuclei, avoid large-scale agglomeration, and reduce particle adhesion. In addition, such growth conditions can promote the growth of primary particles along the surface of the crystal nucleus to the surface of the secondary particles, and present a trend of a specific stacking structure. At the same time, a moderate ammonia value can promote the formation of primary particles with a spindle morphology and a specific size. Too low or too high ammonia values ​​will cause the primary particles to transform into other morphologies.

[0045] The intermittent preparation process of the spherical nickel hydroxide provided by the present invention adopts a complex precipitation method for preparation. By controlling the pH, ammonia value, reaction temperature and other conditions at different stages of the reaction system, the prepared spherical nickel hydroxide exhibits a spindle-shaped primary particle morphology and a specific size, and has good particle uniformity, a narrow particle size distribution, and a high tap density, which can provide a certain mechanical strength and a high energy density for the subsequently prepared positive electrode material.

[0046] In addition, the above preparation method also helps to achieve the orderly arrangement of primary particles along the radial direction of secondary particles, thereby forming spherical or quasi-spherical nickel hydroxide with good particle uniformity, narrow particle size distribution, and high tap density, which can provide certain mechanical strength and higher energy density for the subsequently prepared positive electrode materials, and the radially orderly growth structure can inhibit the pulverization of secondary particles and provide a channel for rapid migration of lithium ions, thereby improving its rate performance.

[0047] In the specific implementation process of the present invention, the pH of the reaction slurry can be regulated by controlling the feed flow rate of the alkali solution, and the ammonia value of the reaction slurry can be regulated by controlling the feed flow rate of the ammonia water.

[0048] In some preferred embodiments, at 45°C, A1 is 11.50-12.30, and A2 is 10.80-11.90, that is, at 45°C, the pH of the reaction slurry in the first stage is 1.50-12.30, and the pH of the reaction slurry in the second stage is 10.80-11.90. In some preferred embodiments, B1 is 0-5 g / L, such as 0, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, or any two thereof; B2 is 2-8 g / L, such as 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, or any two thereof.

[0049] In the present invention, the coprecipitation reaction temperature is 45-55°C, for example, 45°C, 50°C, 55°C or any two thereof, and the first stage time does not exceed 6 hours. By limiting the temperature and time, it is helpful to form primary particles with spindle morphology.

[0050] In the first stage, the stirring speed in the reactor is controlled to be C1; in the second stage, when the product particle size D50 in the reactor reaches 50% to 80% of the target particle size, the stirring speed in the reactor is controlled to be C2; ​​when the product particle size D50 in the reactor reaches more than 80% of the target particle size, the stirring speed in the reactor is controlled to be C3, satisfying C1>C2>C3. In this way, by limiting the nucleation stage to a relatively high speed condition, the dispersion of the crystal nucleus can be improved, agglomeration can be reduced, and the formation of uniform spherical particles can be promoted, while the speed is reduced in the growth stage to avoid the growth of spherical particles due to friction, collision, cracking or even fragmentation.

[0051] The present invention does not limit the specific value range of C1, C2, and C3, as long as C1>C2>C3 is satisfied. In some preferred embodiments, C1 is 400-500 rpm, such as 400 rpm, 420 rpm, 450 rpm, 500 rpm, or a range consisting of any two thereof; and / or, C2 is 350-450 rpm, such as 350 rpm, 400 rpm, 450 rpm, or a range consisting of any two thereof; and / or, C3 is 250-350 rpm, such as 250 rpm, 300 rpm, 350 rpm, or a range consisting of any two thereof.

[0052] In the first stage, the feed rate of the nickel salt solution pumped into the reactor is D1; ​​in the second stage, the feed rate of the nickel salt solution pumped into the reactor is D2, satisfying D1≤D2. By limiting the feed rate of the nickel salt solution in the nucleation stage to be relatively low, the dispersion of the crystal nuclei can be synergistically improved, agglomeration can be reduced, and the width of the particle size distribution can be narrowed. In addition, the feed rate can be increased in the growth stage to promote the growth of the crystal nuclei and improve the output of the synthesis.

[0053] The present invention does not limit the specific value of the feed flow rate, as long as D1≤D2 is satisfied. In some preferred embodiments, D1 is 6 to 20 L / h, for example, 6 L / h, 10 L / h, 15 L / h, 20 L / h or a range consisting of any two thereof; and / or, D2 is 30 to 60 L / h, for example, 30 L / h, 40 L / h, 50 L / h, 60 L / h or a range consisting of any two thereof.

[0054] In some embodiments, before the nickel salt solution, alkali solution and ammonia water are pumped into the reactor, the following steps are also included: adding water as the bottom liquid into the reactor, controlling the stirring speed in the reactor to C1 and the temperature to 45-55°C, and then adding alkali solution and ammonia water to adjust the pH value of the bottom liquid to A1 and the ammonia value to B1. In other words, it is necessary to add water, alkali solution and ammonia water into the reactor in advance as the reaction bottom liquid, and the pH value and ammonia value thereof meet the requirements of the nucleation stage, which can effectively ensure the high repeatability of the preparation method and avoid the influence of fluctuations in the synthesis conditions in the nucleation stage.

[0055] In the specific implementation process of the present invention, pure water is added to the reactor until the stirring blade is covered, the starting speed is set to C1, the temperature is controlled at 45-55°C, and then alkali solution and ammonia water are added to adjust the pH value of the reaction bottom liquid to A1 and the ammonia value to B1; then the nickel salt solution, alkali solution and ammonia water are pumped into the reactor from different pipelines through metering pumps, respectively, to enter the nucleation stage, the initial flow rate of the nickel salt solution is D1, and the feed flow rate of the alkali solution is adjusted by the pH self-feedback adjustment system to maintain the pH value of the reaction slurry in the reactor at 45°C at A1, and the ammonia value of the reaction slurry is maintained at B1 by controlling the feed flow rate of the ammonia solution, and the nucleation stage is maintained at 0.1 ~3h, then the pH is reduced to A2 in 30min and the growth stage is entered. The ammonia value is slowly increased to B2 in about 15h by adjusting the feed flow rate of ammonia water, and then this value is maintained throughout the whole process to promote the orderly growth of the crystal nucleus; from 15h to 25h of synthesis, the feed flow rate of the nickel salt solution is linearly increased from D1 to D2, and this flow rate is maintained until shutdown; when the product particle size D50 in the reactor reaches 50% to 80% of the target particle size, the stirring speed is gradually reduced to C2; when the product particle size D50 in the reactor reaches more than 80% of the target particle size, the stirring speed is gradually reduced to C3, and when D50 grows to the target particle size, the feeding is stopped and the synthesis is completed.

[0056] The present invention can use the following device to implement the above preparation method to obtain spherical nickel hydroxide. Specifically, the reaction device used includes a reactor and a concentrator; wherein the reactor is used to accommodate the reaction slurry and provide the reaction slurry for coprecipitation reaction; the concentrator is used to receive the reaction slurry overflowing from the reactor and provide the reaction slurry for suction filtration and concentration treatment therein; in the second stage, it also includes the following steps: when the liquid level of the reactor reaches the overflow level, the reaction slurry overflows into the concentrator; when the liquid level of the concentrator reaches the preset level, the reaction slurry overflowing into the concentrator is subjected to suction filtration and concentration treatment, and then returned to the reactor. In this way, the liquid levels of the reactor and the concentrator are controlled at the set value, the solid content of the reaction slurry is increased, and on the premise of avoiding the generation of cracked fragments, the generated small particles are promoted to undergo long-term friction, collision, surface dissolution and recrystallization in the reaction system, which helps to improve the sphericity of nickel hydroxide, narrow the particle size distribution of the particles, and reduce the SPAN value.

[0057] In the above embodiment, the overflow liquid level refers to the liquid level in the reactor reaching 60% to 70% of the height of the inner cavity of the reactor, the preset liquid level refers to the liquid level in the concentrator reaching 40% to 80% of the height of the inner cavity of the concentrator, and the stirring speed of the concentrator in the suction filtration concentration process is 250 to 350 rpm.

[0058] In the specific implementation process of the present invention, the above-mentioned reaction device also includes: an input unit, which is used to pump the nickel salt solution, alkali solution and ammonia water into the reactor; a first stirring unit, which is arranged in the reactor and is used to control the stirring speed in the reactor; a second stirring unit, which is used to control the stirring speed in the concentrator, wherein the overflow port of the reactor is connected to the liquid inlet of the concentrator, and the liquid outlet of the concentrator is connected to the reflux port of the reactor.

[0059] The input unit includes a first input unit, a second input unit and a third input unit, the first input unit is used to control the feed flow rate of the nickel sulfate solution, the second input unit is used to control the feed flow rate of the alkali solution, and the third input unit is used to control the feed flow rate of the ammonia solution. Specifically, the first input unit, the second input unit and the third input unit each independently include a metering pump and a pipeline.

[0060] The overflow port of the reactor can be connected to the liquid inlet of the concentrator through an overflow pipe, and the liquid outlet of the concentrator can be connected to the reflux port of the reactor through a reflux pipe. At this time, the overflow pipe can be provided with a concentrator feed valve to control the overflow of the reaction slurry in the reactor to overflow into the concentrator, one end of which is connected to the overflow port of the reactor and the other end is connected to the liquid inlet of the concentrator; a circulating reflux pump can be provided on the reflux pipe to control the reflux of the reaction slurry from the concentrator to the reactor, one end of which is connected to the liquid outlet of the concentrator and the other end is connected to the reflux port of the reactor.

[0061] When the liquid level in the reactor reaches the overflow level, the feed valve of the concentrator and the circulating reflux pump are opened to allow the reaction slurry to overflow into the concentrator; when the liquid level in the concentrator reaches the preset level, the reaction slurry overflowing into the concentrator is filtered and concentrated.

[0062] Among them, a filter rod assembly for implementing suction filtration and concentration can be arranged in the concentrator.

[0063] The reactor is also provided with a pH self-feedback regulating system for controlling the feed flow of the alkali solution according to the set pH value.

[0064] In order to obtain spherical nickel hydroxide, a post-treatment step is further included after the coprecipitation reaction, and the post-treatment includes washing treatment and drying treatment. Specifically, when the material particle size D50 of the reaction slurry in the reactor reaches the target particle size, the feeding is stopped and the synthesis is completed; the reaction slurry in the reactor and the concentrator is collected, and post-treatment processes such as washing treatment and drying treatment are performed to obtain spherical nickel hydroxide.

[0065] The washing treatment includes alkali washing treatment and water washing treatment. Specifically, the reaction slurry in the reactor and the concentrator is collected, centrifuged, alkali washed and water washed in sequence; preferably, the washing liquid used in the alkali washing treatment is a sodium hydroxide solution with a temperature of 50 to 80°C and a concentration of 1 to 4 mol / L; the temperature of the water used in the water washing treatment is 40 to 80°C. The temperature of the drying treatment is 80 to 160°C, and the water is dried to ≤0.2wt%.

[0066] In addition, the post-treatment also includes screening and demagnetization, that is, after the drying, the dried material is sequentially screened and demagnetized to finally obtain spherical nickel hydroxide.

[0067] The present invention does not limit the physical parameters of the nickel salt solution, alkali solution and ammonia water, and can be adjusted according to actual production needs. For example, in some embodiments, the molar concentration of nickel ions in the nickel salt solution is 1.5-3.0 mol / L; the nickel salt in the nickel salt solution includes nickel sulfate; the alkaline substance in the alkali solution includes sodium hydroxide; the molar concentration of the alkaline substance in the alkali solution is 5.0-10.0 mol / L; and the concentration of NH3 in the ammonia water is 3.0-6.0 mol / L.

[0068] The present invention finely controls the parameters of the reaction system, such as pH value, ammonia value, temperature, flow rate, etc., which is not only beneficial to the generation and growth of crystal nuclei, but also beneficial to improving the reproducibility of the preparation method.

[0069] The third aspect of the present invention provides a positive electrode material, which is prepared by sintering raw materials including nickel hydroxide, wherein the nickel hydroxide includes the spherical nickel hydroxide provided by the first aspect or the spherical nickel hydroxide prepared by the preparation method provided by the second aspect.

[0070] Specifically, the spherical nickel hydroxide can be directly subjected to a lithiation sintering treatment to obtain a positive electrode material, or the nickel hydroxide can be mixed with other doping elements and / or coating elements and then subjected to a lithiation sintering treatment to obtain a positive electrode material.

[0071] By sintering the spherical nickel hydroxide with specific morphology and structure, a positive electrode material having both excellent energy density and lithium ion transmission efficiency can be obtained, so that the battery assembled from the positive electrode material has excellent specific capacity and rate performance.

[0072] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0073] like Figure 1 As shown, the reaction device used in the following embodiments and comparative examples includes: a reactor 1, which is used to accommodate the reaction slurry and provide the reaction slurry for coprecipitation reaction therein; a concentrator 2, which is used to receive part of the reaction slurry overflowing from the reactor and provide the reaction slurry for suction filtration and concentration treatment therein, and the concentrator 2 is provided with a filter rod assembly 201 for performing suction filtration and concentration; an input unit 101, which is used to pump the nickel salt solution, alkali solution and ammonia water into the reactor 1, and the input unit 101 includes a first input unit, a second input unit and a third input unit, the first input unit is used to control the feed flow rate of the nickel sulfate solution, the second input unit is used to control the feed flow rate of the alkali solution, and the third input unit is used to control the feed flow rate of the ammonia water, and the first input unit, the second input unit and the third input unit each independently include a metering unit. pump and pipeline; a first stirring unit 102 is arranged in the reactor 1 and is used to control the stirring speed in the reactor 1; a second stirring unit 103 is used to control the stirring speed in the concentrator 2; the overflow port of the reactor 1 is connected to the liquid inlet of the concentrator through an overflow pipeline 104, and the liquid outlet of the concentrator 2 is connected to the reflux port of the reactor 1 through a reflux pipeline 106; the overflow pipeline 104 is provided with a concentrator feed valve 106, which is used to control the overflow of the reaction slurry in the reactor 1 to overflow into the concentrator 2, one end of which is connected to the overflow port of the reactor 1, and the other end is connected to the liquid inlet of the concentrator 2; a circulating reflux pump 3 is arranged on the reflux pipeline 106, which is used to control the reaction slurry to reflux from the concentrator 2 to the reactor 1, one end of which is connected to the liquid outlet of the concentrator 2, and the other end is connected to the reflux port of the reactor 1.

[0074] Example 1

[0075] The preparation method of spherical nickel hydroxide in this embodiment comprises the following steps:

[0076] (1) Preparation of reaction raw materials

[0077] Prepare a nickel sulfate solution with a nickel ion molar concentration of 2.3 mol / L, a sodium hydroxide solution with a sodium hydroxide molar concentration of 8.0 mol / L as an alkali solution, and an ammonia solution with a NH3 molar concentration of 5.0 mol / L;

[0078] (2) Nucleation stage

[0079] Pure water was added to a 500L reactor until the bottom stirring paddle of the first stirring unit was covered. The first stirring unit was turned on, the speed was set to 430rpm, the temperature was controlled at 50±0.5°C, and alkali solution and ammonia water were added to adjust the pH value of the reaction bottom liquid to 12.00±0.05 / 45°C, and the ammonia value was 2.7±0.3g / L; then the nickel sulfate solution, alkali solution and ammonia water were pumped into the reactor from different pipelines through metering pumps, and the initial flow rate of the nickel sulfate solution was 20L / h. The feed flow rate of the alkali solution was adjusted by the pH self-feedback adjustment system so that the pH value of the reaction slurry in the reactor was 12.00±0.05 at 45°C, and the ammonia value of the reaction slurry was 2.7±0.3g / L by controlling the feed flow rate of the ammonia solution. The nucleation stage was maintained for 10min, and then the pH was reduced to 11.80±0.05 (at 45°C) in 30min to enter the growth stage.

[0080] (3) Growth stage

[0081] By adjusting the feed flow rate of ammonia water, the ammonia value slowly climbed to 7.0 g / L in about 15 hours, and then maintained at this value throughout the whole process to promote the orderly growth of crystal nuclei. During the synthesis of 15 to 25 hours, the feed flow rate of nickel sulfate solution linearly climbed from 20 L / h to 50 L / h, and maintained this flow rate until shutdown;

[0082] In the growth stage, when the liquid level in the reactor reaches the overflow level, the feed valve of the concentrator and the circulating reflux pump are opened to allow the reaction slurry to overflow into the concentrator through the overflow pipe, and the reaction slurry of the concentrator is refluxed to the reactor through the reflux pipe and the circulating reflux pump, and the liquid level of the reactor is maintained above or below the overflow level; when the liquid level of the concentrator reaches the preset level, the precision filtration equipment is turned on to filter and concentrate the reaction slurry overflowing into the concentrator, remove excess clear liquid, and increase the solid content of the slurry. The concentrated slurry is returned to the reactor through the circulating reflux pump;

[0083] When the particle size D50 of the material in the reactor grows to 2.5 μm, the stirring speed of the reactor is gradually reduced to 380 rpm within 1 hour and maintained at this speed; when the particle size D50 grows to 3.5 μm, the stirring speed of the reactor is gradually reduced to 320 rpm within 1 hour, and when D50 grows to 4.2 μm (target particle size), the feeding is stopped and the synthesis is completed.

[0084] (4) Post-processing

[0085] After the synthesis is completed, the slurry in the reactor and the concentrator is pumped into a centrifuge through a pipeline for washing. First, it is washed with 2 mol / L alkali solution at 75°C for 40 minutes, and then washed with pure water at 60°C until the pH value is less than 9.5, and then dehydrated and dried; the washed and centrifugally dehydrated material is placed in an oven at a temperature of 100-120°C for drying until the moisture content is less than 0.15%; after drying, the material is collected, sieved with a 300-mesh vibrating screen, and then the magnetic foreign matter in the granular powder is removed by a demagnetization device to obtain a spherical nickel hydroxide product.

[0086] Example 2

[0087] The difference from Example 1 is that in the nucleation stage, the pH value of the base liquid is adjusted to 11.80±0.05 / 45°C, and the ammonia value is 2.7±0.3g / L; the initial flow rate of the nickel sulfate solution is 20L / h; thereafter, the pH value is gradually reduced to 11.50±0.05 (at 45°C) over 30min, and the growth stage is entered; in the growth stage, the pH continues to decrease at the end of the nucleation stage, and gradually decreases to 11.20±0.05 (at 45°C) over 5h, and at the same time, the flow rate of ammonia water is regulated so that the ammonia value slowly climbs to 3.3g / L in about 15h; from 15h to 25h of synthesis, the flow rate of the nickel sulfate solution slowly climbs from 20L / h to 35L / h, and maintains a flow rate of 35L / h until shutdown.

[0088] Comparative Example 1

[0089] The difference from Example 1 is that during the nucleation stage and the growth stage, the pH value of the reaction slurry is maintained at 11.80±0.05 (at 45°C), the ammonia value is 9.0 g / L, and the feed flow rate of the nickel sulfate solution is 50 L / h.

[0090] Comparative Example 2

[0091] The difference from Example 1 is that in the nucleation stage, the pH value and ammonia value of the reaction base liquid and the reaction slurry are 12.30±0.05 (at 45°C) and 8.0 g / L, respectively, and maintained for 3 hours; thereafter, the pH slowly decreases to 11.70±0.05 (at 45°C) over 25 hours, and enters the growth stage; in the growth stage, the feed flow rate of ammonia water is slowly increased over 10 hours during the synthesis for 14 hours to increase the ammonia value from 8.0 g / L to 9.3 g / L, and the flow rate of nickel sulfate solution is directly increased to 15 L / h, 20 L / h, and 30 L / h at 5 hours, 25 hours, and 35 hours of synthesis, respectively, and the reaction temperature is maintained at 65°C throughout the synthesis process.

[0092] Example 3

[0093] The difference from Example 1 is that during the nucleation stage and the growth stage, the feed flow rate of the nickel sulfate solution is 60 L / h throughout the whole process.

[0094] Test example

[0095] 1. Particle size test: Use Malvern laser particle size analyzer (MS-3000) to test D10, D50, D90 and Dmax, and calculate the particle size distribution width SPAN according to the formula (D90-D10) / D50.

[0096] 2. Specific surface area (SSA) test: Use a fully automatic nitrogen adsorption specific surface area tester for testing.

[0097] 3. Tap density (TD) test: Use BT-303 tap density meter for testing.

[0098] The test results of the embodiments and comparative examples are shown in Table 1.

[0099] Table 1

[0100]

[0101] After testing, the spherical nickel hydroxide products of the embodiment and the comparative example are both light green powders. Among them, the secondary particles of the spherical nickel hydroxide product of the embodiment have better sphericity, the particle sizes are basically similar, there are basically no sticking balls, and the primary particles are spindle-shaped; while the spherical nickel hydroxide product of the comparative example is basically spherical, but the sticking balls account for a large proportion, there are obvious fragments, and the primary particles are lath-shaped. Taking the spherical nickel hydroxide product of Example 1 as an example, its SEM image is as follows Figure 2 , Figure 3 , Figure 4 As shown in the figure, it can be seen that the spherical nickel hydroxide of Example 1 includes a plurality of secondary particles, which are formed by stacking primary particles on the surface of the crystal nucleus. The secondary particles are basically single spheres with relatively good sphericity, and the particle sizes are basically close. The primary particles have a spindle-shaped morphology, and the average length of the primary particles is 600-900nm, the average width is 150-250nm, and the length direction deviates from the direction perpendicular to the radial direction of the secondary particles by 0-30°. Taking the spherical nickel hydroxide product of Comparative Example 1 as an example, its SEM picture is as follows Figure 5 , Figure 6 , Figure 7 As shown in the figure, it can be seen that the spherical nickel hydroxide secondary particles of Comparative Example 1 are basically spherical, with a large proportion of sticky balls and obvious fragmentation, and the primary particles are in lath morphology.

[0102] According to Table 1, the present invention uses an intermittent complex precipitation method, and controls the reaction system to undergo a nucleation stage under conditions of higher pH and low ammonia or no ammonia, and undergoes a growth stage under conditions of low pH and medium ammonia. In the nucleation stage, a sufficient amount of crystal nuclei with good dispersion can be obtained, while avoiding large-scale agglomeration. In the growth stage, the average length of the primary particles can be 600-900nm, and the average width can be 150-250nm, which promotes the radial growth of the primary particles and the length direction thereof deviates from the radial direction by 0-30°. At the same time, the medium ammonia environment can promote the growth of the primary particles into a spindle morphology. Too low or too high ammonia value may cause the morphology of the primary particles to change. Under the above-mentioned pH and ammonia value control conditions, precise control of the reaction temperature can promote the growth of the primary particles into a spindle morphology. If the reaction temperature is too high or too low, it is difficult to obtain spindle-shaped primary particles by controlling parameters such as pH and ammonia value.

[0103] At the same time, the present invention adopts a control scheme of high stirring speed in the early stage and gradually reducing the stirring speed in the growth stage. The high speed nucleation and growth in the early stage can effectively improve the dispersion of the crystal nucleus, reduce agglomeration, and promote the formation of uniform spherical secondary particles. At the same time, the reaction time can be extended. The nickel hydroxide prepared by a longer reaction time has a higher tap density. The stirring speed of the reactor is gradually reduced at different time points in the growth stage, which can avoid the cracking and even fragmentation of the grown spherical particles due to friction and collision.

[0104] In summary, the spherical nickel hydroxide provided by the present invention has the characteristics of spindle-shaped primary particles and a specific stacking structure. The primary particles with spindle morphology are tightly stacked together, which increases the surface area of ​​the spherical nickel hydroxide, improves the uniformity during subsequent lithiation sintering, and can also provide a higher specific surface area, thereby increasing the active sites participating in the electrochemical reaction and improving the transmission efficiency of lithium ions; the spherical nickel hydroxide has the characteristics of compact internal stacking, good particle uniformity, and a high tap density, which can provide a higher energy density for the prepared positive electrode material; after lithiation sintering, the prepared positive electrode material will inherit its specific stacking structure, which can significantly reduce the intergranular stress of the positive electrode material and inhibit the pulverization of secondary particles. Under this structure, the diffusion path of lithium ions is shorter, and they can be quickly deintercalated during charging and discharging, with good rate performance.

[0105] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0106] The above description is only a preferred embodiment of the present invention and is 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 spherical nickel hydroxide, characterized in that: The spherical nickel hydroxide includes secondary particles; the secondary particles are formed by stacking primary particles on the surface of the crystal core, wherein the primary particles are spindle-shaped, and the average length of the primary particles is 600-900nm, and the average width is 150-250nm.

2. The spherical nickel hydroxide according to claim 1, characterized in that The particle size distribution width SPAN of the spherical nickel hydroxide is 0.5 to 0.6; and / or the median particle size D50 of the spherical nickel hydroxide is 3.0 to 5.0 μm; and / or the tap density of the spherical nickel hydroxide is 1.9 to 2.2 g / cm 3 ; and / or, the specific surface area of ​​the spherical nickel hydroxide is 6 to 13 m 2 / g; and / or, the length direction of the primary particles deviates from the direction perpendicular to the radial direction of the secondary particles by 0 to 30°.

3. A method for preparing spherical nickel hydroxide according to claim 1 or 2, characterized in that: The method comprises the following steps: pumping a nickel salt solution, an alkali solution and an ammonia solution into a reaction kettle to mix them to form a reaction slurry, and causing the reaction slurry to undergo a coprecipitation reaction to obtain the spherical nickel hydroxide; wherein the coprecipitation reaction comprises a first stage and a second stage; in the first stage, the pH value of the reaction slurry is A1, and the ammonia value is B1; in the second stage, the pH value of the reaction slurry is A2, and the ammonia value is B2, satisfying: A1>A2, B1<B2.

4. The preparation method according to claim 3, characterized in that: At 45°C, A1 is 11.50-12.30; and / or, B1 is 0-5g / L; and / or, at 45°C, A2 is 10.80-11.90; and / or, B2 is 2-8g / L; and / or, the temperature of the coprecipitation reaction is 45-55°C, and the time of the first stage does not exceed 6h; and / or, in the first stage, the stirring speed in the reactor is controlled to be C1; in the second stage, when the product particle size D50 in the reactor reaches 50%-80% of the target particle size, the stirring speed in the reactor is controlled to be C2; ​​when the product particle size D50 in the reactor reaches more than 80% of the target particle size, the stirring speed in the reactor is controlled to be C3, satisfying C1>C2>C3; preferably, C1 is 400-500rpm; and / or, C2 is 350-450rpm; and / or, C3 is 250-350rpm.

5. The preparation method according to claim 3, characterized in that: In the first stage, the feed flow rate of the nickel salt solution pumped into the reactor is D1; ​​in the second stage, the feed flow rate of the nickel salt solution pumped into the reactor is D2, satisfying D1≤D2; preferably, D1 is 6-20 L / h; and / or, D2 is 30~60L / h.

6. The preparation method according to claim 4, characterized in that: Before the nickel salt solution, alkali solution and ammonia water are pumped into the reactor, the following steps are also included: adding water as a bottom liquid into the reactor, controlling the stirring speed in the reactor to C1 and the temperature to 45-55° C., and then adding alkali solution and ammonia water to adjust the pH value of the bottom liquid to A1, The ammonia value is B1; preferably, at 45°C, A1 is 11.50-12.30; and / or, B1 is 0 to 5 g / L; and / or, C1 is 400 to 500 rpm.

7. The preparation method according to claim 3, characterized in that: The reaction device used includes a reactor and a concentrator; wherein the reactor is used to contain the reaction slurry and provide the reaction slurry for coprecipitation reaction therein; the concentrator is used to receive part of the reaction slurry overflowing from the reactor and provide the reaction slurry for suction filtration and concentration treatment therein; In the second stage, the following steps are also included: when the liquid level of the reactor reaches the overflow level, the reaction slurry overflows into the concentrator; when the liquid level of the concentrator reaches the preset level, the reaction slurry overflowing into the concentrator is filtered and concentrated, and then returned to the reactor; preferably, the overflow level refers to the liquid level in the reactor reaching 60% to 70% of the height of the reactor cavity, and the preset level refers to the liquid level in the concentrator reaching 40% to 80% of the height of the concentrator cavity, and the stirring speed of the concentrator in the filtration and concentration process is 250 to 350 rpm.

8. The preparation method according to claim 3, characterized in that: After the coprecipitation reaction, washing treatment and drying treatment are also included; wherein the washing treatment includes alkali washing treatment and water washing treatment; preferably, the washing liquid used in the alkali washing treatment is a sodium hydroxide solution with a temperature of 50-80°C and a concentration of 1-4 mol / L; preferably, the temperature of the water used in the water washing treatment is 40-80°C; preferably, the temperature of the drying treatment is 80-160°C, and the water is dried to ≤0.2wt%.

9. The preparation method according to claim 3, characterized in that: The molar concentration of nickel ions in the nickel salt solution is 1.5 to 3.0 mol / L; and / or, the nickel salt in the nickel salt solution includes nickel sulfate; and / or, the alkaline substance in the alkali solution includes sodium hydroxide; and / or, the molar concentration of the alkaline substance in the alkali solution is 5.0 to 10.0 mol / L; and / or, the concentration of NH3 in the ammonia water is 3.0 to 6.0 mol / L.

10. A positive electrode material, characterized in that: The nickel hydroxide is prepared by sintering raw materials including nickel hydroxide, wherein the nickel hydroxide includes the spherical nickel hydroxide according to claim 1 or 2 or the spherical nickel hydroxide prepared by the preparation method according to any one of claims 3 to 9.

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