A precursor and a method of making the same

Abstract

The application discloses a precursor and a preparation method thereof, to avoid the problem that the electrochemical performance of a positive material prepared by using a large-particle precursor is poor due to the fact that the large-particle precursor is easy to crack. x Co y Mn z (OH)2, the precursor is a secondary particle composed of primary particles, the secondary particle has a median particle size D 50 ≥ 9 μm; wherein 0.40 ≤ x ≤ 0.98, 0 ≤ y ≤ 0.50, 0 ≤ z ≤ 0.50, and x + y + z = 1; in the secondary particle, the number of surface crack-containing particles is less than or equal to 2, and the number of the surface crack-containing particles is obtained by shooting an SEM image with a magnification of 1.0K.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a precursor and a preparation method thereof. BACKGROUND

[0002] As a secondary battery, lithium ion batteries have become the mainstream in new energy batteries. The performance of the positive electrode material in the lithium ion battery has become the main research object for improving the performance of the lithium ion battery, and the performance of the positive electrode material is greatly affected by the precursor.

[0003] Currently, the ternary precursor mainly composed of nickel, cobalt and manganese is the main raw material for the positive electrode material. Due to the influence of the preparation method, when the particle size of the precursor is large, large cracks may appear on the surface of the particles, and even the phenomenon of cracked balls may occur. This further leads to a significant decrease in the electrochemical performance of the positive electrode material prepared by sintering the precursor, such as capacity decay. Therefore, the problem of cracked balls in the ternary precursor needs to be solved. SUMMARY

[0004] The present application provides a precursor and a preparation method thereof to avoid the problem of poor electrochemical performance of the positive electrode material prepared by the large particle precursor due to the cracked balls.

[0005] In a first aspect, the present application provides a precursor, the molecular expression formula of the precursor is: Ni x Co y Mn z (OH)2, the precursor is a secondary particle composed of primary particles, the median particle size D 50 of the secondary particle is greater than or equal to 9 μm; and

[0006] 0 < z < 0.50, and x + y + z = 1; in the secondary particle, the number of surface crack-containing particles is less than or equal to 2, and the number of surface crack-containing particles is obtained by shooting SEM images with a magnification of 1.0K.

[0007] In a possible implementation, in the secondary particle, the number of small particles is less than or equal to 2; wherein the small particles are particles with a particle size less than 60% of D 50 , and the number of small particles is obtained by shooting SEM images with a magnification of 1.0K.

[0008] In a possible implementation, the particle size distribution SPAN of the secondary particle is 0.30-0.65.

[0009] In a possible implementation, the BET of the secondary particle is 7-20 m 2 / g.

[0010] One possible implementation, △D 50 / D 50 <5%; of which, △D 50 The median particle size D of the secondary particles 50 The median particle size D' of the secondary particles after compression 50 The difference between them.

[0011] In one possible implementation, the roundness γ of the secondary particles is greater than 0.980; where γ = 4πS / L 2 S is the area of ​​the cross-section passing through the geometric center of the secondary particle, and L is the perimeter of the cross-section.

[0012] In one possible implementation, the porosity of the secondary particles is 3%-10%; wherein the porosity of the secondary particles is obtained by cross-sectional testing through the geometric center of the secondary particles.

[0013] In one possible implementation, on a cross-section passing through the geometric center of the secondary particle, the porosity of the first target region is less than 5%, and the porosity of the second target region is greater than 5%; wherein,

[0014] The first target region is a circular region on the cross-section with the geometric center as the center and a radius of 30% of the radius of the inscribed circle of the cross-section. The second target region is an annular region on the cross-section with an inner circle of 50% of the radius of the inscribed circle of the cross-section and an outer circle of the inscribed circle of the cross-section.

[0015] Secondly, embodiments of this application provide a method for preparing the precursor described in the first aspect and any possible implementation, comprising:

[0016] In the first reaction apparatus, soluble nickel salt, soluble cobalt salt, and soluble manganese salt undergo a co-precipitation reaction in a solvent to generate seed crystals and grow them, thereby obtaining a first slurry with a first solid content; wherein the first solid content is 300-1000 g / L.

[0017] The first slurry is passed into a second reaction device containing the solvent to obtain a second slurry with a second solid content; wherein the second solid content is less than the first solid content;

[0018] The soluble nickel salt, the soluble cobalt salt, and the soluble manganese salt are co-precipitated in the second slurry, and the particles in the second slurry grow into the precursor to obtain a third slurry with a third solid content; wherein the third solid content is greater than the second solid content and less than or equal to the first solid content.

[0019] The first pH of the first slurry is greater than the second pH of the second slurry, and the second pH is greater than or equal to the third pH of the third slurry; the third pH is 10-12.

[0020] One possible implementation of the coprecipitation reaction includes conditions in which a complexing agent is included in the reaction system.

[0021] In one possible implementation, the median particle size of the particles in the third slurry is 1.5 to 5 times the median particle size of the particles in the first slurry.

[0022] In one possible implementation, the first pH includes a first sub-pH and a second sub-pH; the first sub-pH is 11-14, the second sub-pH is greater than 10, and the first sub-pH is greater than the second sub-pH;

[0023] In the first reaction apparatus, soluble nickel salt, soluble cobalt salt, and soluble manganese salt undergo a co-precipitation reaction in a solvent to generate seed crystals and grow them, yielding a first slurry with a first solid content, comprising:

[0024] Under the conditions of the first pH, the soluble nickel salt, the soluble cobalt salt, and the soluble manganese salt undergo the co-precipitation reaction under the complexing action of the complexing agent to generate the seed crystals; wherein the median particle size of the seed crystals is 0.25-0.5 times the median particle size of the particles in the first slurry;

[0025] Under the conditions of the second pH, the seed crystals are grown into particles in the first slurry to obtain the first slurry.

[0026] In one possible implementation, in either the first or second reaction apparatus, the soluble nickel salt, the soluble cobalt salt, and the soluble manganese salt undergoing the co-precipitation reaction each enter the first reaction apparatus in the form of a first solution and the second reaction apparatus in the form of a second solution; wherein,

[0027] The average flow rate of the first solution is less than the average flow rate of the second solution.

[0028] The embodiments of this application provide one or more possible implementations, which have at least the following beneficial effects:

[0029] First, the precursor provided in this application has the characteristics of large particle size and almost no cracks in the particles, thereby avoiding the problem of capacity decay in the cathode material prepared by sintering when the precursor includes particles with surface cracks or even cracked spherical particles.

[0030] Secondly, the precursor provided in this application has a small number of small particles, which can avoid the problem of decreased electrochemical performance of the cathode material, such as capacity, caused by excessive sintering of small particles when the precursor participates in the sintering preparation of cathode material.

[0031] Furthermore, the precursor particles are characterized by a compact interior and a loose exterior. Consequently, the porosity of the first target region on its cross-section is low, while the porosity of the second target region on the outer circumference is high. This gives the precursor particles the advantages of high BET (Breakpoint Equivalence) and good sphericity.

[0032] Finally, in the precursor preparation method provided in this application embodiment, when a first slurry with high solid content (i.e., first solid content) is generated by the co-precipitation reaction, the seed crystals can grow into particles with good sphericity under relatively high collision intensity and frequency during the growth process. Then, by passing this first slurry into a second reaction device, the particles in the first slurry can continue to grow in a system with low viscosity and low supersaturation, and the collision intensity and frequency between particles are reduced, avoiding the occurrence of surface cracks or even spherical fragmentation as the particle size increases.

[0033] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The purposes and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not intended to limit this disclosure. Attached Figure Description

[0034] Figure 1a An electron microscope image of the precursor in Example 1 at a magnification provided in this application embodiment;

[0035] Figure 1b An electron microscope image of the precursor in Example 1 at a magnification provided in this application embodiment;

[0036] Figure 1c An electron microscope image of the precursor in Example 1 at a magnification provided in this application embodiment;

[0037] Figure 1d An electron microscope image of the precursor in Example 1 at a magnification provided in this application embodiment;

[0038] Figure 1e An electron microscope image of the precursor in Example 1 at a magnification provided in this application embodiment;

[0039] Figure 1fAn electron microscope image of the precursor in Example 1 at a magnification provided in this application embodiment;

[0040] Figure 2a An electron microscope image of the precursor in Example 3 at a magnification provided in this application embodiment;

[0041] Figure 2b An electron microscope image of the precursor in Example 3 at a magnification provided in this application embodiment;

[0042] Figure 2c An electron microscope image of the precursor in Example 3 at a magnification provided in this application embodiment;

[0043] Figure 3a An electron microscope image of the precursor in Example 7 at a magnification provided in this application embodiment;

[0044] Figure 3b An electron microscope image of the precursor in Example 7 at a magnification provided in this application embodiment;

[0045] Figure 3c An electron microscope image of the precursor in Example 7 at a magnification provided in this application embodiment;

[0046] Figure 3d An electron microscope image of the precursor in Example 7 at a magnification provided in this application embodiment;

[0047] Figure 3e An electron microscope image of the precursor in Example 7 at a magnification provided in this application embodiment;

[0048] Figure 3f An electron microscope image of the precursor in Example 7 at a magnification provided in this application embodiment;

[0049] Figure 4a This application provides an electron microscope image of the precursor in Comparative Example 1 at a magnification provided in an embodiment of the present application;

[0050] Figure 4b This application provides an electron microscope image of the precursor in Comparative Example 1 at a magnification provided in an embodiment of the present application;

[0051] Figure 4c This application provides an electron microscope image of the precursor in Comparative Example 1 at a magnification provided in an embodiment of the present application;

[0052] Figure 4d This application provides an electron microscope image of the precursor in Comparative Example 1 at a magnification provided in an embodiment of the present application;

[0053] Figure 4e This application provides an electron microscope image of the precursor in Comparative Example 1 at a magnification provided in an embodiment of the present application;

[0054] Figure 5a An electron microscope image of the precursor in Comparative Example 3 at a magnification provided in this application embodiment;

[0055] Figure 5b An electron microscope image of the precursor in Comparative Example 3 at a magnification provided in this application embodiment;

[0056] Figure 5c An electron microscope image of the precursor in Comparative Example 3 at a magnification provided in this application embodiment;

[0057] Figure 5d An electron microscope image of the precursor in Comparative Example 3 at a magnification provided in this application embodiment;

[0058] Figure 5e An electron microscope image of the precursor in Comparative Example 3 at a magnification provided in this application embodiment;

[0059] Figure 5f An electron microscope image of the precursor in Comparative Example 3 at a magnification provided in this application embodiment;

[0060] Figure 6a An electron microscope image of the precursor in Comparative Example 4 at a magnification provided in this application embodiment;

[0061] Figure 6b An electron microscope image of the precursor in Comparative Example 4 at a magnification provided in this application embodiment;

[0062] Figure 6c An electron microscope image of the precursor in Comparative Example 4 at a magnification provided in this application embodiment;

[0063] Figure 6d An electron microscope image of the precursor in Comparative Example 4 at a magnification provided in this application embodiment;

[0064] Figure 6e An electron microscope image of the precursor in Comparative Example 4 at a magnification provided in this application embodiment;

[0065] Figure 6f An electron microscope image of the precursor in Comparative Example 4 at a magnification provided in this application embodiment;

[0066] Figure 7 Electron micrograph of the cross-section of the precursor in Embodiment 3 provided for the present application;

[0067] Figure 8 Electron micrograph of the cross-section of the precursor in Comparative Example 3 provided for the embodiments of this application;

[0068] Figure 9Electron micrograph of the cross-section of the precursor in Embodiment 1 provided for the present application;

[0069] Figure 10 Electron micrograph of the cross-section of the precursor in Comparative Example 2 provided for the embodiments of this application;

[0070] Figure 11a Electron micrograph of the cross-section of the precursor in Embodiment 7 provided for the present application;

[0071] Figure 11b Electron micrograph of the cross-section of the precursor in Embodiment 7 provided for the present application;

[0072] Figure 12 Electron micrograph of the cross-section of the precursor in Comparative Example 3 provided for the embodiments of this application;

[0073] Figure 13a Electron micrograph of the cross-section of the precursor in Comparative Example 4 provided for the embodiments of this application;

[0074] Figure 13b Electron micrograph of a cross-section of the precursor in Comparative Example 4 provided for embodiments of this application. Detailed Implementation

[0075] To address the issue of insufficient electrochemical performance in cathode materials prepared using precursor fragmentation, this application provides a method with the molecular formula Ni. x Co y Mn z The precursor of (OH)2 is a secondary particle composed of primary particles, with a median particle size D of the secondary particles. 50 ≥9μm. Because the number of particles with surface cracks in the secondary particles is less than or equal to 2, these secondary particles contain almost no or no cracked spheres. This avoids the problem of insufficient electrochemical performance of the cathode material prepared based on the precursor due to cracked spheres in the precursor.

[0076] The following provides a detailed description of a precursor and its preparation method according to embodiments of this application. It should be noted that the embodiments described below are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0077] This invention provides a precursor, the molecular formula of which is: Ni x Co y Mn z (OH)2. The precursor is a secondary particle composed of primary particles, with a median particle size greater than or equal to 9 μm.

[0078] Where 0.40≤x≤0.98, 0≤y≤0.50, 0≤z≤0.50, and x+y+z=1.

[0079] Of the aforementioned secondary particles, the number of particles with surface cracks is less than or equal to 2. Preferably, the number of particles with surface cracks is 0.

[0080] In some embodiments, the median particle size of the secondary particles is less than or equal to 18 μm.

[0081] Since the sintering temperature during the preparation of cathode materials is determined by the particle size of most of the secondary particles in the precursor, in order to further avoid the problem of over-sintering when some of the secondary particles are too small, the number of small particles in the above-mentioned secondary particles is less than or equal to 2.

[0082] Among them, small particles are secondary particles with a particle size smaller than D. 50 60% of the particles.

[0083] The number of small particles and the number of particles with surface cracks were obtained by SEM imaging at 1.0K magnification with dimensions of 126±1.0μm in length and 89±1.0μm in width. The following is a detailed description in two parts:

[0084] First, when counting the number of small particles, N samples can be taken, and M regions of each sample can be photographed at a magnification of 1.0K, resulting in N×M SEM images of the secondary particles. The number of small particles is determined by observation and measurement of each SEM image. During measurement, the two points furthest apart on the particle in the SEM image can be selected as the particle size for measurement. When the measured particle size is smaller than D... 50 When 60% of the particles are small, they are marked as small particles, and the total number of small particles in all SEM images is taken as the number of small particles.

[0085] For sizes significantly larger than D 50 or greater than D 50 60% of the particles are no longer measured. The aforementioned N≥2, M≥4.

[0086] Secondly, when counting the number of particles with cracks on the surface, similarly, take N samples and take M images of each sample at a magnification of 1.0K to obtain N×M SEM images of secondary particles. Observe and count them to obtain the number of particles with cracks on the surface. Figures 1a-1f An SEM image of a secondary particle surface with cracks, provided in an embodiment of this application, is shown below. Figures 1a-1f As shown, the crack is obviously easy to count at a magnification of 1.0K.

[0087] The cracks on the surface of the particles mentioned above are actually caused by the increased inertia resulting from particle growth during the manufacturing process, as the particle size increases and the inertia increases under the action of stirring shear force and axial force. Therefore, the aforementioned particles with surface cracks are mainly large particles. Here, "large particles" refers to particles in the secondary particle category, relative to smaller particles.

[0088] Furthermore, the particle size distribution (SPAN) of the aforementioned secondary particles is 0.30-0.65, indicating that these secondary particles possess relatively uniform size and small particle size differences between each other. The SPAN is calculated using the following formula:

[0089]

[0090] In some embodiments, the tap density (TD) of the aforementioned secondary particles is 1.5-2.5 g / cm³. 3 The ratio of loose density to tapped density is 0.8-0.95.

[0091] Furthermore, the roundness γ of the aforementioned secondary particles is greater than 0.980; where γ = 4πS / L 2 S is the area of ​​the cross-section passing through the geometric center of the secondary particle, and L is the perimeter of the cross-section.

[0092] The aforementioned cross-section passing through the geometric center of the secondary particle is the cross-section with the largest area among the secondary particle cross-sections.

[0093] The porosity of the aforementioned secondary particles is 3%-10%. The porosity of these secondary particles is obtained by cross-sectional testing through the geometric center of the secondary particles.

[0094] Because the secondary particles have a compact internal structure and a loose external structure, the porosity of these secondary particles is the average porosity across the cross-section. Furthermore, in this cross-section, the porosity of the first target region located in the middle is less than 5%, while the porosity of the second target region located on the outer periphery is greater than 5%.

[0095] The first target region is a circular area on the cross-section with its geometric center as the center and a radius equal to 30% of the radius of the inscribed circle of the cross-section. The second target region is an annular area on the cross-section with an inner circle equal to 50% of the radius of the inscribed circle of the cross-section and an outer circle equal to the inscribed circle of the cross-section.

[0096] It should be noted that the roundness and porosity of the secondary particles, as well as the porosity of the first and second target regions, were all obtained by calculating the average value of the maximum profile measurements of at least 20 particles.

[0097] In some embodiments, the specific surface area (BET) of the secondary particles is 7-20 m². 2 / g.

[0098] Furthermore, the D of the secondary particle 50 With the compressed D' 50 The difference △D 50 When the value is close to 0, the aforementioned secondary particles are less prone to deformation, exhibiting strong pressure resistance and thus demonstrating the advantage of high capacity. Specifically, ΔD 50 / D 50 <5%. The compression pressure is less than or equal to 0.5T, and the pressure holding time is no more than 60s. One possible implementation is to compress 2g of dried and sieved secondary particles at 0.5T for 5s using a powder compaction density tester, and then perform particle size testing on the compressed sample to obtain the median particle size D' after compression. 50 .

[0099] It should be noted that in the molecular expressions of this application, the subscripts are atomic indices, used to represent the relative molar content between corresponding atoms in the molecule. For example, Ni x Co y Mn z M k In (OH)₂, x, y, z, and k are atomic indices, representing the relative molar amounts of Ni, Co, Mn, and dopant M in the molecule, respectively. For example, x represents the molar proportion of Ni in the hydroxide.

[0100] Based on the same inventive concept, this application also provides a method for preparing a precursor, which includes the following steps:

[0101] Step 101: In the first reaction apparatus, soluble nickel salt, soluble cobalt salt, and soluble manganese salt undergo a co-precipitation reaction in a solvent to generate seed crystals and grow them, thereby obtaining a first slurry with a first solid content.

[0102] Specifically, the seed crystals are also secondary particles composed of primary particles. The first pH of the co-precipitation used in this step to obtain the first slurry with the first solid content is 10-14.

[0103] The aforementioned first reaction apparatus may be a first reaction vessel. The aforementioned solvent may be water.

[0104] In the initial stages of seed crystal formation and growth, a high solids content enhances the collision intensity and frequency between particles, thereby ensuring good sphericity of the particles in the initial stage and guaranteeing that the target product inherits this sphericity. Therefore, the initial solids content is 300-1000 g / L.

[0105] In some embodiments, the soluble nickel salt includes at least one selected from nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate. The soluble cobalt salt includes at least one selected from cobalt sulfate, cobalt nitrate, cobalt chloride, and nickel acetate. The soluble manganese salt includes at least one selected from manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride. The solvent includes water.

[0106] Furthermore, the conditions for the above coprecipitation reaction may also include: the reaction system containing a complexing agent. This complexing agent may include ammonia and / or sodium citrate.

[0107] Furthermore, the two stages of seed crystal generation and growth described above can be controlled by different pH levels. After generating a certain number of seed crystals at the first pH level, the seed crystals continue to grow in the acidic or alkaline environment of the second pH level, forming a relatively compact internal structure within the precursor particles, i.e., the particulate matter in the first slurry. The faster the seed crystals grow, the more pores are left inside, and the larger the corresponding BET of the target product, thus achieving the control of BET in the target product. A detailed description follows:

[0108] The aforementioned first pH includes a first sub-pH and a second sub-pH. The first sub-pH is 11-14, the second sub-pH is greater than 10, and the first sub-pH is greater than the second sub-pH.

[0109] To obtain the first slurry, soluble nickel salt, soluble cobalt salt, and soluble manganese salt are first subjected to a co-precipitation reaction under the complexation effect of a complexing agent at a first pH condition to generate seed crystals. The ratio of the median particle size of the seed crystals to the median particle size of the particles in the first slurry is 0.25-0.5.

[0110] Then, by reducing the amount of pH adjuster entering the first reaction device, the first sub-pH is reduced to the second sub-pH.

[0111] In this way, while the co-precipitation reaction continues in the first reaction device, the aforementioned seed crystals continue to grow under the second pH condition until they grow into particles in the first slurry, thus obtaining the first slurry. At this point, the particle size of the particles in the first slurry is taken as the reaction endpoint.

[0112] Furthermore, this application provides two embodiments for adding soluble nickel salt, soluble cobalt salt, and soluble manganese salt to a reaction vessel:

[0113] The first method involves adding an appropriate amount of water to the reactor, followed by feeding the metal salts into the reactor at a preset frequency. This preset frequency, and the amount added each time, should be set so that the metal salts entering the reactor each time can react fully.

[0114] The second method involves first adding a small amount of water to the reaction vessel. Then, soluble nickel salt, soluble manganese salt, and soluble cobalt salt are prepared into a mixed salt solution of a preset concentration, allowing the soluble nickel salt, soluble manganese salt, and soluble cobalt salt to enter the reaction vessel in solution form for a co-precipitation reaction.

[0115] The aforementioned reaction vessel can be either a first reaction vessel or a second reaction vessel as described below. The first and second embodiments described above can be used individually or in combination. Furthermore, the soluble nickel salt, soluble cobalt salt, and soluble manganese salt added to the respective reaction vessels should be maintained in a predetermined ratio.

[0116] It should be noted that while the co-precipitation reaction is taking place in the first reactor, the slurry is simultaneously circulating in the transfer vessel and thickener connected to the first reactor. At this time, the first reaction equipment includes the first reactor, the first transfer vessel, and the first thickener. The same applies to the second reactor described below.

[0117] Step 102: Pass the first slurry into a second reaction device containing the solvent to obtain a second slurry with a second solid content.

[0118] The second solid content is less than the first solid content. The second reaction equipment may include a second reaction vessel, and after the first slurry enters the second reaction vessel, it circulates in the second transfer vessel and the second thickener of the second reaction equipment.

[0119] The number of second reaction devices can be one, two, or more. Preferably, the number of second reaction devices is four to ten; then the first slurry will be divided into portions corresponding to the number of second reaction devices and fed into the second reaction vessel respectively.

[0120] Specifically, the second solid content can be 10–300 g / L. Obviously, compared to the first slurry, the second slurry has a higher solvent content (e.g., water), so the solid content of the second slurry is reduced. However, since no reactants are added in this step, the particles in the second slurry are the same as those in the first slurry, and the median particle size is obviously the same.

[0121] When the first slurry is introduced into the second reaction vessel containing the solvent, the vessel may also contain a pH adjuster and a complexing agent solution. The concentration of the complexing agent solution may be 2-10 g / L, and the complexing agent solution may be ammonia water. The pH adjuster may be a sodium hydroxide solution.

[0122] Furthermore, the second pH of the second slurry is lower than the aforementioned first pH. The second pH is 10-12.

[0123] Step 103: The soluble nickel salt, soluble cobalt salt and soluble manganese salt continue to undergo a co-precipitation reaction in the second slurry, so that the particles in the second slurry can grow into precursors, and a third slurry with a third solid content is obtained.

[0124] The content of the third solid is greater than that of the second solid, but less than or equal to that of the first solid.

[0125] The first pH of the first slurry is greater than the second pH of the second slurry, and the second pH is greater than the third pH of the third slurry, with the third pH being 10-12.

[0126] Specifically, similar to the first and second slurries, the pH of the third slurry can also be controlled by a pH adjuster. This pH adjuster can be, for example, NaOH. Furthermore, the concentration of the complexing agent in the third slurry can be equal to or different from the concentration of the complexing agent in the first slurry.

[0127] Due to the increased solvent content in the second slurry, the viscosity of the particles in the second slurry in the second reactor decreases. Therefore, metal ions are more easily dispersed in this step. Especially under the stirring action of the rotor in the reactor, the instantaneous ion concentrations of nickel, cobalt, and manganese ions are low when soluble nickel, cobalt, and manganese salts enter the second reaction equipment. According to the formula for calculating supersaturation:

[0128] H = ([M) 2+ ][OH - ] 2 ) / K sp，M(OH)2 ), where [M 2+ ] is free metal ion M 2+ The concentration of [OH-] is the free OH-. - The concentration of K sp，M(OH)2 It is the solubility product of M(OH)2.

[0129] It can be seen that the instantaneous supersaturation of the solution in the second reaction vessel decreases. This further increases the ion dispersion rate in the second reaction equipment, making the environment in the second reaction equipment conducive to particle growth in the second slurry.

[0130] Under the aforementioned growth environment, the particles in the second slurry continue to grow under the co-precipitation reaction, and the high-intensity collisions between particles with increasing particle size are effectively avoided, so that the final third slurry contains almost no particles with surface cracks.

[0131] In some embodiments, the median particle size of the particles in the third slurry is 1.5-5 times the median particle size of the particles in the first slurry. Because the particle size increase in the third slurry is greater than that in the first slurry, the portion formed in the third slurry is more porous, while the portion formed in the first slurry and the internal structure of the particles are more compact. This is represented in the particle cross-section as two circles with different porosities: the inner circle represents the portion grown in the first slurry, and the outer circle represents the portion formed in the third slurry. Therefore, the ratio of the radii of the outer circle to the inner circle is consistent with the ratio of the median particle size of the particles in the third slurry to the median particle size of the particles in the first slurry.

[0132] Furthermore, the rate at which soluble nickel salt, soluble cobalt salt, and soluble manganese salt are added to the second reactor is greater than the rate at which they are added to the first reactor, so that the precursor secondary particles form a structure with a compact interior and a loose exterior, thereby achieving the purpose of preparing the target BET secondary particles.

[0133] For example, soluble nickel salts, soluble cobalt salts, and soluble manganese salts are introduced into the first and second reactors as soluble nickel salt solutions, soluble manganese salt solutions, and soluble cobalt salt solutions, respectively. On the one hand, the proportions of soluble nickel salts, soluble cobalt salts, and soluble manganese salts in the solutions added to the first and second reactors remain consistent. On the other hand, the average rate at which the soluble nickel salt solutions, soluble manganese salt solutions, and soluble cobalt salt solutions are introduced into the first reactor is lower than the average rate at which the corresponding solutions are introduced into the second reactor. As a result, the particle size of the particles in the second reaction device grows and increases, thereby making the portion of the particles in the second slurry that grows into the particles in the third slurry more porous.

[0134] The following detailed description is provided through examples and comparative examples.

[0135] (I) Preparation

[0136] Example 1

[0137] S1. Prepare a reaction solution containing nickel sulfate, manganese sulfate, and cobalt sulfate according to the molar ratio of Ni:Co:Mn = 92:4:4. Prepare a complexing agent of 5 mol / L ammonia water and a pH adjuster of 15 mol / L sodium hydroxide solution.

[0138] (In the first reaction vessel)

[0139] S2. Add ammonia solution, sodium hydroxide solution, and pure water to the first reaction vessel to form a reaction base liquid with a corresponding pH of 12.2.

[0140] S3. Under pH 1 acidic / alkaline conditions, a nickel-cobalt-manganese mixed metal salt solution, sodium hydroxide solution, ammonia solution, and protective gas nitrogen are introduced concurrently into the first reaction vessel to generate particles with a median particle size of 1.4 μm.

[0141] S4. By controlling the flow rate of sodium hydroxide, the pH1 is lowered to pH2 (11.2), and the pH is maintained at 2 to continue the co-precipitation reaction, resulting in target particles with a median particle size of the second preset value and a first slurry with a solid content S1 of 500 g / L. The second preset value is 5 μm.

[0142] In steps S2-S4, the average flow rate of the metal salt during the reaction process is 500 L / h, and the flow rate of ammonia water is adjusted according to the concentration of ammonia water in the solution. The concentration of ammonia water during the reaction process is maintained at 3-3.3 g / L.

[0143] (In the second reactor)

[0144] S5. Add sodium hydroxide solution to the second reactor to make the pH 3 11. Add the first slurry to the second reactor and circulate it through the second reactor, the second transfer reactor, and the second thickener to obtain a second slurry with a solid content S2 of 50 g / L.

[0145] S6. A reaction solution (i.e., a nickel-cobalt-manganese mixed metal salt solution), sodium hydroxide solution, ammonia solution, and protective nitrogen gas are simultaneously introduced into the second reactor. The pH is maintained at 10.5 until the median particle size of the second slurry reaches the third preset value. The reactor is then shut down and the feed is stopped. At this point, a third slurry with a solid content S3 of 450 g / L is obtained. Here, the third preset value is 13 μm.

[0146] S7. Wash, dry, sieve, and remove iron from the particulate matter in the third slurry to obtain the precursor;

[0147] In steps S5-S7, the average flow rate of the reaction solution is 1000 L / h, and the flow rate of ammonia water is adjusted according to the concentration of ammonia water in the solution. The concentration of ammonia water in the second reaction vessel is 5-5.3 g / L.

[0148] Examples 2-8, Comparative Examples 1-3

[0149] The preparation process can be the same as that in Example 1. The differences are in the reaction conditions, the median particle size of the particles, the solid content S1, S2, and S3 during the reaction, the specific differences in reaction conditions, and the differences in the physicochemical properties of the final product, as shown in Tables 1 and 2.

[0150] Comparative Example 4

[0151] The entire reaction, from start to finish, takes place in the same reactor. The detailed reaction steps are as follows:

[0152] S1. Prepare a reaction solution containing nickel sulfate, manganese sulfate, and cobalt sulfate according to the molar ratio of Ni:Co:Mn = 92:4:4. Prepare the complexing agent: 5 mol / L ammonia solution, pH adjuster, and 15 mol / L sodium hydroxide solution.

[0153] S2. Add ammonia solution, sodium hydroxide solution, and pure water to the first reaction vessel to form a reaction base liquid with a corresponding pH of 11.2.

[0154] S3. Under pH 1 acidic / alkaline conditions, a nickel-cobalt-manganese mixed metal salt solution, sodium hydroxide solution, ammonia solution, and protective gas nitrogen are introduced concurrently into the first reaction vessel to generate particles with a median particle size of a first preset value. This first preset value is 4.5 μm.

[0155] S4. By controlling the flow rate of sodium hydroxide, the pH1 is reduced to pH2 10.5, and the pH2 is maintained to continue the co-precipitation reaction, so as to obtain target particles with a median particle size of the second preset value and a slurry with a solid content S1 of 450 g / L; the third preset value is 17 μm.

[0156] S5. Wash, dry, sieve, and remove iron from the particulate matter in the first slurry to obtain the precursor;

[0157] In steps S2-S4, the average flow rate of the metal salt during the reaction process is 1000 L / h, and the flow rate of ammonia water is adjusted according to the concentration of ammonia water in the solution. The concentration of ammonia water during the reaction process is 5-5.3 g / L.

[0158] Table 1

[0159]

[0160]

[0161] (II) Measurement

[0162] First, a SEM image with a length of 126.7 μm and a width of 89.4 μm was obtained using a Thermo Fisher Apreo 2S microscope. Specifically, SEM images were taken from random samples of the precursor from Example 1. By adjusting the lens magnification and the imaging area, SEM images of the precursor at different magnifications and in different imaging areas were obtained. Figure 1a , Figure 1b , Figure 1c , Figure 1d , Figure 1e , Figure 1f .

[0163] SEM images of the precursor were taken after random sampling in Example 3. The lens magnification and shooting area were adjusted to obtain SEM images of the precursor in different shooting areas at different magnifications.Figure 2a , Figure 2b , Figure 2c .

[0164] SEM images of the precursor were taken after random sampling in Example 7. The lens magnification and shooting area were adjusted to obtain SEM images of the precursor in different shooting areas at different magnifications. Figure 3a , Figure 3b , Figure 3c , Figure 3d , Figure 3e , Figure 3f .

[0165] SEM images of the precursors in Comparative Example 1 were captured after random sampling. Lens magnification and shooting area were adjusted to obtain SEM images of the precursors in different shooting areas at different magnifications. Figure 4a , Figure 4b , Figure 4c , Figure 4d , Figure 4e .

[0166] SEM images of the precursors in Comparative Example 3 were captured after random sampling. Lens magnification and shooting area were adjusted to obtain SEM images of the precursors in different shooting areas at different magnifications. Figure 5a , Figure 5b , Figure 5c , Figure 5d , Figure 5e , Figure 5f .

[0167] SEM images of the precursors in Comparative Example 4 were captured after random sampling. Lens magnification and shooting area were adjusted to obtain SEM images of the precursors in different shooting areas at different magnifications. Figure 6a , Figure 6b , Figure 6c , Figure 6d , Figure 6e , Figure 6f .

[0168] As can be seen, in the SEM images taken at magnifications of 1.0K and below, the particle surfaces of the precursors in the examples do not contain cracks, while the comparative examples include multiple particles containing cracks.

[0169] Furthermore, SEM images of the cross-section of the precursor in Example 3 were taken to obtain... Figure 7 SEM images of the cross-section of the precursor in Comparative Example 3 were obtained. Figure 8 SEM images of the cross-section of the precursor in Example 1 were obtained. Figure 9 SEM images of the cross-section of the precursor in Comparative Example 2 were obtained. Figure 10 SEM images were taken of different cross-sections of the precursor in Example 7, and the results were obtained. Figures 11a-11bSEM images of the cross-section of the precursor in Comparative Example 3 were obtained. Figure 12 SEM images were taken of different cross-sections of the precursor in Comparative Example 4, and the results were obtained. Figures 13a-13b .

[0170] Then, using a laser particle size analyzer, the D of the precursor was tested. 90 D 10 D 50 , to calculate SPAN.

[0171] The specific surface area (BET) of the precursor was measured using an automated nitrogen adsorption surface area analyzer.

[0172] The tapped density (TD) and loose packing density (AD) were tested using a tapped density tester.

[0173] D' was tested using a laser particle size analyzer 50 Then calculate D 50 With D' 50 The difference, and △D 50 / D 50 .

[0174] The roundness of the precursor was obtained by testing the cross-sections of 20 randomly selected secondary particles using an electron scanning microscope and calculating the average roundness of each cross-section.

[0175] The roundness of each precursor is measured using the following formula: γ = 4πS / L 2 S is the area of ​​the maximum cross-section of the precursor (i.e., the cross-section passing through the geometric center of the secondary particle), and L is the perimeter of the maximum cross-section. Test data are shown in Table 2.

[0176] Table 2

[0177]

[0178]

[0179] Furthermore, the precursor secondary particles were sectioned, and 20 sections passing through the geometric center of the precursor were randomly selected. SEM images of the sections were obtained by combining electron microscopy to determine the ratio of the void area to the section area, and the porosity of each section was obtained. The average porosity of the 20 sections was calculated.

[0180] Simultaneously, on the aforementioned 20 randomly selected cross-sections, a first target region is determined with the geometric center as the center and a radius equal to 30% of the inscribed circle of the cross-section. A second target region is defined as the annular region formed by the inner circle (still centered at the geometric center) and the outer circle (also centered at 50% of the inscribed circle of the cross-section), and the outer circle (also an inscribed circle of the cross-section).

[0181] The ratio of the void area to the cross-sectional area in the first target region of each cross-section is determined and the average value is calculated to obtain the porosity A1 of the inner layer structure of the precursor particles.

[0182] The ratio of the void area to the cross-sectional area in the second target region of each cross-section was determined, and the average value was calculated to obtain the porosity A2 of the external structure of the precursor particles. See Table 3 for specific data.

[0183] Table 3

[0184]

[0185]

[0186] As shown in Tables 2 and 3, due to the presence of fine powder, the corresponding SPAN values ​​of Comparative Examples 1 and 3 are greater than 0.65. Compared with Comparative Examples 1 and 3, the SPAN values ​​of the Examples are all less than 0.5, showing good particle size uniformity.

[0187] Because of the high solid content S3 in Comparative Example 2, the system has high viscosity, making it difficult for metal ions to disperse in the system, resulting in high local supersaturation. This leads to a decrease in the specific surface area of ​​Comparative Example 2 and makes it easy to generate small particles.

[0188] Further comparative examples and comparative examples 2-4, and Figure 10 , Figure 12 As shown by -13, cracks exist in the secondary particles of Comparative Example 2-4. Therefore, under a pressure of 0.5T, Comparative Example 2-4 is more prone to splitting, which is reflected in the higher ΔD50 / D50 of Comparative Example 2-4.

[0189] Further integration Figures 13a-13b As can be seen in Comparative Example 4, the current driving particles grow into large particles in the same reaction from beginning to end. Their internal structure is compact and there is no obvious distinction between the internal and external structures. In the end, most of the finished secondary particles crack and there are a large number of small particles.

[0190] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A precursor, characterized in that, The molecular formula of the precursor is: Ni x Co y Mn z (OH)2, the precursor is a secondary particle composed of primary particles, and the median particle size D of the secondary particles is... 50 ≥9μm; Wherein, 0.40≤x≤0.98, 0≤y≤0.50, 0≤z≤0.50, and x+y+z=1; among the secondary particles, the number of particles with surface cracks is less than or equal to 2, and the number of particles with surface cracks is obtained by taking a SEM image at a magnification of 1.0K; On the cross-section passing through the geometric center of the secondary particles, the porosity of the first target region is less than 5%, and the porosity of the second target region is greater than 5%; wherein, the first target region is a circular region on the cross-section with the geometric center as the center and a radius of 30% of the radius of the inscribed circle of the cross-section, and the second target region is an annular region on the cross-section with an inner circle of 50% of the radius of the inscribed circle of the cross-section and an outer circle of the inscribed circle of the cross-section; △D 50 / D 50 <5%; where △D 50 The median particle size D of the secondary particles 50 The median particle size D' of the secondary particles after compression 50 The difference between them.

2. The precursor as described in claim 1, characterized in that, In the secondary particles, the number of small particles is less than or equal to 2; wherein, the small particles are those with a particle size smaller than D. 50 60% of the particles, the number of which was obtained by taking a SEM image at 1.0K magnification.

3. The precursor as described in claim 1 or 2, characterized in that, The particle size distribution (SPAN) of the secondary particles is 0.30-0.

65.

4. The precursor as described in claim 1, characterized in that, The porosity of the secondary particles is 3%-10%; wherein, the porosity of the secondary particles is obtained by cross-sectional testing through the geometric center of the secondary particles.

5. The precursor as described in claim 1, characterized in that, The roundness γ of the secondary particles is greater than 0.980; where γ = 4πS / L 2 S is the area of ​​the cross-section passing through the geometric center of the secondary particle, and L is the perimeter of the cross-section.

6. The precursor as claimed in claim 1, characterized in that, The BET of the secondary particles is 7-20m. 2 / g.

7. A method for preparing the precursor according to any one of claims 1-6, characterized in that, include: In the first reaction apparatus, soluble nickel salt, soluble cobalt salt, and soluble manganese salt undergo a co-precipitation reaction in a solvent to generate seed crystals and grow them, thereby obtaining a first slurry with a first solid content; wherein the first solid content is 300-1000 g / L. The first slurry is passed into a second reaction device containing the solvent to obtain a second slurry with a second solid content; wherein the second solid content is less than the first solid content; The soluble nickel salt, the soluble cobalt salt, and the soluble manganese salt are co-precipitated in the second slurry, and the particles in the second slurry grow into the precursor to obtain a third slurry with a third solid content; wherein the third solid content is greater than the second solid content and less than or equal to the first solid content; the first pH of the first slurry is greater than the second pH of the second slurry, and the second pH is greater than or equal to the third pH of the third slurry; the third pH is 10-12.

8. The method as described in claim 7, characterized in that, The median particle size of the particles in the third slurry is 1.5 to 5 times that of the median particle size of the particles in the first slurry.

9. The method as described in claim 7 or 8, characterized in that, The first pH includes a first sub-pH and a second sub-pH; the first sub-pH is 11-14, the second sub-pH is greater than 10, and the first sub-pH is greater than the second sub-pH; In the first reaction apparatus, soluble nickel salt, soluble cobalt salt, and soluble manganese salt undergo a co-precipitation reaction in a solvent to generate seed crystals and grow them, yielding a first slurry with a first solid content, comprising: Under the conditions of the first pH, the soluble nickel salt, the soluble cobalt salt, and the soluble manganese salt undergo the co-precipitation reaction under the complexing action of the complexing agent to generate the seed crystals; wherein the median particle size of the seed crystals is 0.25-0.5 times the median particle size of the particles in the first slurry; Under the conditions of the second pH, the seed crystals are grown into particles in the first slurry to obtain the first slurry.

Images