A precursor of ternary positive electrode material and preparation method thereof

Abstract

The present invention provides a precursor of a ternary positive electrode material and a preparation method thereof, which is used to provide a precursor of a ternary positive electrode material with uniform size and suitable specific surface area, so as to improve the rate performance of the corresponding positive electrode material. The molecular formula of the ternary precursor is: Ni x Co y Mn z (OH)2; wherein 0.4≤x≤0.8, 0.1≤y≤0.3, 0.2≤z≤0.6, x+y+z=1; the specific surface area of ​​the precursor is 10-30m 2 / g, and the particle size distribution of the precursor is less than 0.68; the particle size distribution is #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of cathode material precursors, and in particular to a precursor of a ternary cathode material and a preparation method thereof. Background Art

[0002] At present, the preparation methods of ternary precursors (i.e., precursors of ternary positive electrode materials) are mainly divided into two categories: continuous method and intermittent method. The continuous method refers to a method in which feeding and discharging are carried out simultaneously during the reaction process, and the reaction slurry overflows to the aging kettle through the overflow pipe and stands to obtain the target product. The continuous method has the advantage of high production capacity, but due to its characteristic of "feeding and discharging simultaneously", the reactor includes reactants entering at different times, which correspondingly include crystals in different growth stages, that is, there is a problem that the residence time distribution of the reactants in the reactor is wide, resulting in a wide distribution of product particle size. This leads to overburning of small particles during sintering to prepare positive electrode materials, or incomplete sintering of large particles, which in turn leads to poor quality of positive electrode materials.

[0003] The intermittent method means that during the reaction process, the slurry in the reactor is concentrated by a thickener, and after removing the clear liquid, the remaining slurry is circulated back to the reactor to allow the crystals to continue to grow and age to obtain the target product. Therefore, when the precursor is prepared by the intermittent method, the particle size distribution of the prepared precursor is narrower than that of the precursor prepared by the continuous method under the same conditions because the residence time of the reactants in the reactor is relatively uniform. Accordingly, the positive electrode material corresponding to the precursor prepared by the intermittent method has better performance than the positive electrode material corresponding to the precursor prepared by the continuous method.

[0004] However, in the intermittent preparation process, due to the concentration effect of the thickener, the solid content of the slurry increases after passing through the thickener, which significantly increases the intensity and frequency of collisions between solid particles. This leads to the problem of low specific surface area of ​​the final precursor particles, which in turn leads to poor performance of the corresponding positive electrode material such as rate performance. Summary of the invention

[0005] The present invention provides a precursor of a ternary positive electrode material and a preparation method thereof, so as to provide a precursor of a ternary positive electrode material with uniform size and suitable specific surface area, so as to improve the rate performance of the corresponding positive electrode material.

[0006] In a first aspect, the present invention provides a precursor of a ternary cathode material, wherein the molecular formula of the ternary precursor is: Ni x Co y Mn z (OH)2; wherein 0.4≤x≤0.8, 0.1≤y≤0.3, 0.2≤z≤0.6, x+y+z=1;

[0007] The specific surface area of ​​the precursor is 10-30m 2 / g, and the particle size distribution of the precursor is less than 0.68; the particle size distribution is

[0008] The precursor of the above-mentioned ternary cathode material has a small specific particle size distribution, that is, the advantage of uniform particle size, and the specific surface area is between 10-30m 2 / g, thus avoiding the problem in the prior art that the positive electrode material has poor lithium ion insertion and extraction performance during the charge-discharge process due to the low specific surface area of ​​the precursor.

[0009] In a possible implementation manner, the sphericity γ of the precursor is greater than 0.96; wherein γ = 4πS / L 2 , S is the area of ​​the largest cross-section of the precursor, and L is the perimeter of the largest cross-section.

[0010] In a possible implementation manner, the porosity of the precursor is 5%-12%, and the cross-sectional area of ​​the pores on any cross section of the precursor is not greater than 2000nm. 2 .

[0011] In a possible implementation manner, on any cross-section of the precursor, the radius of the inner circle is 1.5-2.5 μm, and the ratio of the inner circle to the outer circle is 0.4-0.7; wherein the outer circle is the circumscribed circle of the cross-section, the inner circle is a concentric circle with the outer circle, and the area of ​​the largest pore on the inner circle is not greater than 1.3% of the area of ​​the smallest pore.

[0012] In a possible implementation manner, the ratio between the (001) crystal plane spacing and the (101) crystal plane spacing of the precursor is D(001) / D(101)=3C; wherein C is a preset constant, and C is 0.95-1.10.

[0013] In a possible implementation manner, the precursor is a secondary particle composed of primary particles, the primary particles are strip-shaped, the thickness of the primary particles is 20-200 nm, and the length of the primary particles is 0.17-0.7 μm; the median particle size D of the precursor is 50 3-5μm.

[0014] In a possible implementation manner, the tap density of the precursor is 1.2-2 g / cm 3 .

[0015] In a possible implementation manner, the content of sodium impurities in the precursor is less than 100 ppm, and the content of sulfur impurities is less than 1000 ppm.

[0016] In a second aspect, the present application provides a method for preparing a precursor of a ternary cathode material as described in the first aspect and any one of the above, comprising:

[0017] A mixed salt solution, an alkaline solution and a complexing agent are subjected to a coprecipitation reaction for 3-6 hours under the condition that the reaction atmosphere is nitrogen and the pH of the reaction environment is in a first pH range, to generate a first slurry including target seed crystals; wherein the mixed salt solution includes a nickel salt solution, a cobalt salt solution, and a manganese salt solution, and the alkaline solution includes a sodium hydroxide solution and / or a potassium hydroxide solution; the first pH range is 11.4-11.8, and the median particle size of the seed crystals is 1.5-1.8 μm;

[0018] Discharging the supernatant in the first slurry to obtain a second slurry; wherein the second slurry includes the target seed crystals;

[0019] Lowering the pH of the reaction environment to a second pH range within 12 hours, so that the target seed crystals in the second slurry continue to grow under the action of the coprecipitation reaction under the condition that the reaction atmosphere includes oxygen, to obtain an intermediate precursor; wherein the median particle size of the intermediate precursor is 2-3 μm, and the lower limit of the second pH range is not less than 10.0;

[0020] The intermediate precursor is allowed to continue to grow into a target precursor under the action of the coprecipitation reaction under the condition that the reaction atmosphere includes oxygen and the pH of the reaction environment is in a third pH range; wherein the lower limit of the third pH range is not less than 10.0, and the median particle size of the target precursor is 3-5 μm.

[0021] In a possible implementation manner, the second pH range and the third pH range are both 10.4-11.2.

[0022] In a possible implementation manner, the complexing agent is ammonia water, the alkaline solution is a sodium hydroxide solution, and the mixed salt solution, the alkaline solution and the complexing agent are subjected to a coprecipitation reaction for 3-6 hours under the condition that the reaction atmosphere is nitrogen and the pH value of the reaction environment is in the first pH range to generate a first slurry including target seed crystals, comprising:

[0023] A sodium hydroxide solution with a concentration of 4-15 mol / L and an ammonia solution with a concentration of 1-8 mol / L are introduced into the reaction device, and nitrogen is introduced into the reaction device, so that the ammonia content in the reaction device is 2-6 g / L, the pH value of the reaction environment is 11.0-12.0, and the nitrogen content is not less than 99%; wherein the flow rate of the nitrogen is 100-200 L / min;

[0024] The mixed salt solution is introduced into the reaction device at a flow rate of 160-200 L / h, so that the nickel salt, cobalt salt and manganese salt in the mixed salt solution undergo a coprecipitation reaction for 3-6 hours under the condition that the pH value is in the first pH range, to generate the target seed crystals and obtain the first slurry; wherein the concentration of the mixed salt solution is 1.2-2 mol / L.

[0025] A possible implementation manner is that before lowering the first pH value to the second pH range within 12 hours, the method further includes:

[0026] The flow rate of the mixed salt solution is increased to 300-500 L / h at an increase rate of 50%-90%; and the flow rate of oxygen is increased. The increased oxygen flow rate is determined according to the following formula:

[0027] Wherein, K1 is a preset constant, K1 is 4%-15%; V1 is the flow rate of the increased oxygen, and V2 is the flow rate of the mixed salt solution.

[0028] In a possible implementation manner, the reaction temperature in the reaction device is 50-70° C.; and the stirring speed of the rotor in the reaction device is 250 r / min-400 r / min.

[0029] In a possible implementation manner, before the intermediate precursor is allowed to continue to grow into a target precursor under the action of a coprecipitation reaction under the condition that the reaction atmosphere includes oxygen and the pH of the reaction environment is in a third pH range, the method further includes:

[0030] The flow rate of the mixed salt solution was increased to 500-600 L / h at an increase rate of 25%-70%.

[0031] In a third aspect, the present application also provides a method for predicting the specific surface area of ​​a precursor of a ternary cathode material prepared by the method described in the second aspect and any one of the aspects, comprising:

[0032] Among them, K2 is the preset constant, K2 is 90-110, and the unit of K2 is L×g / m 2 , V is the total amount of oxygen introduced into the oxygen reaction device, B is the specific surface area of ​​the ternary precursor, the unit of the total amount of oxygen is L, and the unit of the specific surface area is m 2 / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1a A scanning electron microscope image of the target precursor in Example 1 provided in the embodiments of the present application (the shooting magnification is 10K);

[0034] Figure 1b A scanning electron microscope image of the target precursor in Example 1 provided in the embodiments of the present application (the shooting magnification is 30K);

[0035] Figure 2 A schematic diagram of the cross-section structure of a precursor of a ternary cathode material provided in an embodiment of the present application;

[0036] Figure 3 A scanning electron microscope image of the target precursor in Example 2 provided in the embodiments of the present application;

[0037] Figure 4 A scanning electron microscope image of the target precursor in Example 3 provided in the embodiments of the present application;

[0038] Figure 5 A scanning electron microscope image of the target precursor in Example 4 provided in the embodiments of the present application;

[0039] Figure 6 Scanning electron microscope images of the cross-section of the target precursor in Examples 1-4 provided in the embodiments of the present application;

[0040] Figure 7 This is a scanning electron microscope image of the target precursor of Comparative Example 1 provided in the embodiments of the present application;

[0041] Figure 8 A scanning electron microscope image of a cross section of a target precursor of Comparative Example 1 provided in the embodiments of the present application;

[0042] Fig. 9 This is a scanning electron microscope image of the target precursor of Comparative Example 2 provided in the embodiments of the present application;

[0043] Fig.10 This is a scanning electron microscope image of the target precursor of Comparative Example 3 provided in the embodiments of the present application;

[0044] Fig.11 This is a scanning electron microscope image of the target precursor of Comparative Example 4 provided in the embodiments of the present application. DETAILED DESCRIPTION

[0045] In view of the lack of a ternary cathode material precursor with uniform size and suitable specific surface area in the prior art, the present invention proposes a ternary cathode material precursor Ni x Co y Mn z (OH)2, 0.4≤x≤0.8, 0.1≤y≤0.3, 0.2≤z≤0.6, x+y+z=1; the specific surface area of ​​the precursor is 10-30m 2 / g, particle size distribution is less than 0.68, particle size distribution is

[0046] The precursor has the advantage of having a consistent particle size because its particle size distribution is less than 0.68. At the same time, the increase in the specific surface area of ​​the precursor is beneficial to the deintercalation of lithium ions in the positive electrode material, thereby increasing the lithium ion transmission channels in the positive electrode material, shortening the diffusion path of lithium ions, and effectively improving the rate performance of the positive electrode material; therefore, the precursor provided in the present embodiment also has the characteristic of suitable specific surface area, that is, the present embodiment, by appropriately increasing the specific surface area of ​​the precursor, not only avoids the problem of the prior art that it is difficult to prepare a high-rate positive electrode material due to the small specific surface area of ​​the precursor, but also avoids the problem of decreased capacity of the positive electrode material due to excessive specific surface area.

[0047] Furthermore, the sphericity γ of the above-mentioned precursor is greater than 0.96. The sphericity of the precursor is obtained by the following formula: γ = 4πS / L 2 , wherein S is the area of ​​the largest cross-section of the precursor, and L is the perimeter of the largest cross-section.

[0048] Furthermore, the secondary particles are secondary particles composed of primary particles, the primary particles are strip-shaped, and the primary particles are loosely stacked, so the morphology of the secondary particles is loose. The porosity of the precursor is 5%-12%.

[0049] In the embodiments of the present application, the length of a primary particle refers to the distance between the two points of any primary particle that are farthest apart in the longitudinal direction, and the thickness refers to the distance between the two points of any primary particle that are farthest apart in the transverse direction. That is, the length is the longest length of the primary particle in the long side direction, and the thickness is the longest length of the primary particle in the narrow side direction. Accordingly, the ratio of the length to the thickness of the primary particle is measured by determining the distance between the two farthest points in the longitudinal direction and the distance between the two farthest points in the transverse direction. Specifically, it can be measured on a SEM with a high magnification, such as an SEM with a magnification of 30K, see Figure 1b .

[0050] Further, on any cross section of the precursor, the ratio of the inner circle to the outer circle is 0.4-0.7; wherein the outer circle is the circumscribed circle of the cross section, the inner circle is a concentric circle with the outer circle, and the area of ​​the largest pore on the inner circle is not greater than 1.3% of the area of ​​the smallest pore; that is, on the cross section of the precursor, the pores of the inner circle are evenly distributed, and because the primary particles of the outer circle are thin strips under oxidation, they are radially distributed. Figure 2 ; The diameter of the outer circle is related to the formation of long strip-shaped primary particles during the precursor preparation process, that is, it is related to the refinement of the primary particles.

[0051] Furthermore, the porosity of the precursor is 5%-12%, and the cross-sectional area of ​​the pores on any cross section of the precursor is not greater than 2000nm. 2 The area of ​​the pores may be, for example, 400-2000 nm. 2 . Continue to refer to Figure 2 It can be obtained that the larger the distance between the primary particles on the outer circle of the precursor cross section, that is, the looser the primary particles are stacked, the higher the degree of growth during the preparation process, and the larger the cross-sectional area obtained by the same cutting method.

[0052] The porosity of the above-mentioned precursor is obtained by averaging the porosities of N sections of M precursors, where M and N are both positive integers. For example, M precursor particles are randomly selected from a batch of precursors for sectioning, and each precursor is sectioned N times. Then, the average value of the ratio of the cross-sectional area of ​​the pores on the N sections of each precursor particle to the area of ​​the section where the pores are located is determined in turn, and the porosity of each corresponding precursor particle is obtained respectively, and then the porosity of the precursor particles is added and divided by M to obtain the porosity of the above-mentioned precursor. That is, the porosity of the above-mentioned precursor is the average value of the ratio of the cross-sectional area of ​​the pores on multiple sections to the area of ​​the section where the pores are located.

[0053] The above cross-sectional area or the void area on the cross-sectional area is obtained by depicting, measuring and calculating the high-magnification SEM image using software.

[0054] Furthermore, since oxygen is introduced into the precursor when the seed crystal grows to a corresponding size (i.e., the median particle size is 1.5-1.8 μm) during the preparation process, and the pH of the reaction environment decreases slowly with the change of the reaction stage, in the precursor provided in the embodiment of the present application, the ratio between the (001) crystal plane spacing and the (101) crystal plane spacing is D(001) / D(101)=3C; wherein C is a preset constant, and C is 0.95-1.10.

[0055] Furthermore, the thickness of the primary particles of the above precursor is 20-200 nm, the length of the primary particles is 0.17-0.7 μm, and the median particle size D 50 3-5μm.

[0056] Furthermore, the tap density of the precursor is 1.2-2 g / cm 3 .

[0057] Furthermore, the content of sodium impurities in the above-mentioned precursor is less than 100 ppm, and the content of sulfur impurities is less than 1000 ppm.

[0058] Among them, the above impurities are mainly ionic Na + , SO4 2-, and can be obtained through ICP (inductively coupled plasma) testing.

[0059] Based on the same inventive concept, a method for preparing a precursor of the above-mentioned ternary positive electrode material is provided below, which is used to prepare a precursor with a concentrated particle size distribution and a large specific surface area. The method comprises the following implementation steps:

[0060] Step 101: a mixed salt solution, an alkaline solution and a complexing agent are subjected to a coprecipitation reaction for 3-6 hours under the condition that the reaction atmosphere is nitrogen and the pH value of the reaction environment is in a first pH range, to generate a first slurry including target seed crystals.

[0061] The mixed salt solution includes a nickel salt solution, a cobalt salt solution and a manganese salt solution, and the first pH range is 11.4-11.8.

[0062] Specifically, under the first pH condition, the growth rate of the target seed crystal is much lower than the generation rate of the target seed crystal, and the median particle size of the target seed crystal is maintained at 1.6-1.7 μm. The mixed salt solution flow rate in this step is relatively low (160-200 L / h), and the reaction time is 3-6 hours to generate a sufficient number of target seed crystals.

[0063] The above-mentioned reaction equipment can be a reactor. The reaction temperature is 50-70°C; and the stirring rate of the rotor in the reaction equipment is 250r / min-400r / min. In one embodiment of the present application, the pH of the reaction environment is controlled by introducing an alkaline solution into the reactor. The alkaline solution can be a sodium hydroxide solution and / or a potassium hydroxide solution.

[0064] The complexing agent may be ammonia water or a soluble ammonium salt, such as ammonium sulfate, ammonium nitrate, or ammonium bicarbonate.

[0065] Specifically, in order to avoid the problem of oxidation due to the action of oxygen in the seed generation stage, which leads to the agglomeration of primary particles, the embodiment of the present application strictly controls the reaction atmosphere in step 101 to make it nitrogen. And in order to ensure that at the beginning of the coprecipitation reaction, the pH of the reaction environment is a pH interval that is easy to generate seed crystals. First, a sodium hydroxide solution (i.e., sodium hydroxide solution) with a concentration of 4-15mol / L and ammonia water of 1-8mol / L are passed into the reaction device to make the pH of the reaction environment 11.0-12.0. At the same time, nitrogen is passed into the reaction device so that the content of ammonia in the reaction device is 2-6g / L. That is, nitrogen is passed so that the nitrogen content in the reaction device is not less than 99%, and the oxygen content is less than 1%, so as to avoid the seed crystals being oxidized in the generation stage.

[0066] Then, a mixed salt solution, ammonia water and alkaline solution are introduced into the reaction device at a flow rate of 160-200 L / min, so that the pH value of the reaction environment in the above-mentioned reaction device is in the first pH range, so that the nickel salt, cobalt salt and manganese salt in the mixed salt solution undergo a coprecipitation reaction with the alkaline solution under the complexing action of the complexing agent ammonia water.

[0067] The molar concentration of metal ions in the nickel salt and the mixed salt solution is 1.2-2 mol / L.

[0068] Furthermore, in order to avoid the problem that the target crystal seeds of the mixed salt solution, alkaline solution and complexing agent are agglomerated and have poor sphericity when entering the reaction equipment when the content of the mixed solution, alkaline solution and the like in the equipment reactor is low at the beginning of the reaction, in one embodiment of the present application, the slurry in the reaction equipment can also be overflowed when the reaction in this step occurs, so as to achieve the purpose of replacing the crystal seeds whose sphericity does not meet the requirements in the early slurry, thereby ensuring that the sphericity γ of the precursor is greater than 0.96; wherein γ=4πS / L 2 , S is the area of ​​the largest cross-section of the precursor, and L is the perimeter of the largest cross-section.

[0069] Step 102: draining the supernatant in the first slurry to obtain a second slurry.

[0070] Wherein, the second slurry includes an intermediate precursor.

[0071] Specifically, the supernatant discharged from the first slurry can be passed through the first slurry in the reaction device into a thickener, and the second slurry is obtained through the thickening effect of the thickener, and the second slurry is refluxed into the aforementioned reaction device.

[0072] Since step 102 follows step 101, discharging the clear water means that the median path or particle size distribution of the target crystal seeds generated in the reaction equipment meets the preset requirements, that is, under the action of overflow, the target crystal seeds with uneven morphology generated at the initial stage of the reaction due to the instability of the system in the reactor and other reasons have been completely eliminated, so the overflow valve opened when executing step 101 can be closed at this time.

[0073] It should be noted that, in the embodiment of the present application, after the supernatant in the first slurry is discharged in step 102, in order to avoid the problem of unstable liquid level in the reaction equipment leading to unstable reaction system, the flow rate of the discharged supernatant can be the sum of the flow rates of the salt solution, alkaline solution and ammonia solution in the reactor. Accordingly, after the thickener is opened, it will no longer be closed, and only the overflow valve (of the transfer kettle) will be closed, so that the slurry circulates between the thickener, the transfer kettle and the reactor to ensure the stability of the liquid level in the reaction equipment and the reaction system.

[0074] Step 103: lowering the pH of the reaction environment to a second pH range within 12 hours, so that the target seed crystals in the second slurry continue to grow under the action of the coprecipitation reaction under the condition that the reaction atmosphere includes oxygen, to obtain an intermediate precursor.

[0075] The median particle size of the intermediate precursor is 2-3 μm, and the lower limit of the second pH range is not less than 10.0.

[0076] Specifically, the method of lowering the pH to the second pH range may be to reduce the pH corresponding to the target seed crystal by a relatively uniform pH reduction of 0.6-1 within 12 hours.

[0077] After a sufficient number of target seed crystals are generated, the pH of the reaction environment is lowered, which can increase the size of the target seed crystals. That is, as the reactants (i.e., the continuous introduction of mixed salt solution, complexing agent, and alkali solution) increase, co-precipitation reaction continues to occur in the reaction equipment, and the newly generated primary particles are evenly coated on the surface of the target seed crystals layer by layer, thereby increasing the size of the target seed crystals.

[0078] Further, in order to make the target seed crystal grow more efficiently as an intermediate precursor, the flow rate of the above-mentioned mixed salt solution, complexing agent and alkaline solution (for example, sodium hydroxide solution) can be increased in this step 102. Specifically, in order to avoid the flow rate increase rate from disturbing the balance of the coprecipitation reaction system too fast, thereby affecting the uniformity of the primary particle size of the product, that is, when the target seed crystal is generated and the pores in the target seed crystal are evenly distributed, the flow rate of the mixed salt solution is appropriately increased so that the size of the target seed crystal continues to grow as the flow rate of the mixed salt solution increases. The increase rate of the flow rate of the mixed salt solution is 50%-90%, so that the flow rate of the mixed salt solution in this step is 300-500L / h. For example, the flow rate in step 101 is 200L / h, and the flow rate of the increased mixed salt solution can be 300L / h. Based on the flow rate increase ratio of this salt solution, the flow rate of the alkaline solution is increased to maintain the reaction environment in the reaction equipment in the second pH interval.

[0079] At the same time, the flow rate of the ammonia solution is increased in proportion to the flow rate increase of the salt solution, so that the ammonia content in the reaction equipment (eg, reactor) is maintained within 2-6 g / L.

[0080] Furthermore, since the sphericity of the seed crystal in the generation stage is decisive for the sphericity of the final product, when the seed crystal grows to the target seed crystal with good sphericity, the oxidation treatment will not only not cause the agglomeration of the primary particles and affect the sphericity of the target seed crystal or the final product, but also can refine the primary particles by oxidizing the divalent manganese ions in the target seed crystal, that is, the target seed crystal increases in size under the action of the atmosphere including oxygen, and the thickness of the primary particles decreases, so that the primary particles are loosely packed and have a large specific surface area (see further). Figure 2 ), and the porosity of the intermediate precursor is better than the porosity of the target seed crystal.

[0081] In the embodiments of the present application, the reaction atmosphere in the reaction device may include oxygen by introducing oxygen into the reaction device; introducing a mixed gas of oxygen and nitrogen into the reaction device; or introducing a mixed gas of oxygen and nitrogen into the reaction device.

[0082] At the same time, this step 103 controls the oxygen introduction stage: when the seed crystal grows to the corresponding size (i.e., the median particle size is 1.5-1.8 μm); and the pH of the reaction environment is slowly lowered corresponding to the change of the reaction stage, so that the ratio between the (001) crystal plane spacing and the (101) crystal plane spacing in the precursor is D(001) / D(101)=3C; wherein C is a preset constant, C is 0.95-1.10.

[0083] It should be noted that although turning on the thickener in step 102 is beneficial for the particles (i.e., target crystal seeds) in the reactor to always be in the same growth stage, i.e., uniform in size, as the solid content increases, the frequency and intensity of collisions between the particles increase, which is not conducive to obtaining a high specific surface area for the target crystal seeds during the growth process. At this time, the introduction of oxygen or a mixed gas containing oxygen can refine the primary particles of the target crystal seeds, thereby effectively alleviating the problem of a decrease in specific surface area caused by the densification of the primary particles of the target crystal seeds due to the increase in solid content.

[0084] Furthermore, in order to make the target crystal seeds oxidized uniformly during their growth, the flow rate of the oxygen introduced can be increased as the flow rate of the mixed salt solution increases. That is, as the number of target crystal seeds increases, the increase in the oxygen flow rate is controlled to be consistent with the increase in the flow rate of the mixed salt solution, ensuring that the primary particles of the target crystal seeds in the reaction environment can continue to grow in a direction away from their center, that is, ensuring that the primary particles of all target crystal seeds continue to grow radially, thereby being refined, and then ensuring that the specific surface area is 10-30m 2 / g of precursor. That is:

[0085]

[0086] Wherein, K1 is a preset constant, K1 is 4%-15%; V1 is the flow rate of the increased oxygen, V2 is the flow rate of the mixed salt solution. The unit of V1 is L / min, and the unit of V2 is L / h.

[0087] It should be noted that when the gas introduced is a mixed gas, in order to avoid waste of nitrogen and the impact of gas flow on the reaction environment, the sum of the flow rates of oxygen and nitrogen or oxygen and nitrogen must be kept unchanged. Therefore, as the oxygen content introduced into the reaction equipment increases, the flow rate of nitrogen introduced should be adaptively reduced.

[0088] Step 104: The intermediate precursor is allowed to continue to grow into a target precursor under the effect of the above coprecipitation reaction under the condition that the reaction atmosphere includes oxygen and the pH value of the reaction environment is within a third pH range.

[0089] Among them, the median particle size of the target precursor is 3-5 μm, and the lower limit of the third pH range is not less than 10.0.

[0090] In one embodiment of the present application, the second pH interval and the third pH interval are both 10.4-11.2.

[0091] When the intermediate precursor in the second slurry continues to increase with the introduction of alkali solution, mixed salt solution and complexing agent, the flow rate of the mixed salt solution can be further increased, and the increase rate of the mixed salt solution flow rate can be 25%-70%. The flow rate of the increased mixed salt solution is not less than 500L / h. The flow rates of the alkaline solution (for example, sodium hydroxide solution and complexing agent) can also be increased with reference to the increase rate of the mixed salt solution, and the pH in the reaction equipment is maintained in the third pH range, and the ammonia content is 2-6g / L.

[0092] Due to the increase in solid content in the second slurry, the collision intensity and collision frequency of the intermediate precursor increase under the stirring action of the reaction equipment. During the crystal growth process, the collision between crystals will make the primary particles located on the surface of the crystal coarse and dense, thereby making it difficult to increase the specific surface area of ​​the target precursor (i.e., the secondary particles composed of the primary particles). In order to suppress this change, in the embodiment of the present application, under the premise that the pH of the reaction environment is in the third pH interval, oxygen is continuously introduced to refine the newly generated primary particles on the surface of the intermediate precursor, thereby increasing the specific surface area of ​​the secondary particles. When the median particle size of the intermediate precursor increases to 3-5 μm, the target precursor is obtained.

[0093] Furthermore, the present embodiment also provides a method for predicting the specific surface area of ​​the precursor of the ternary cathode material prepared by the above method, comprising:

[0094] Among them, K2 is the preset constant, K2 is 90-110, and the unit of K2 is L×g / m 2 , V is the total amount of oxygen introduced into the oxygen reaction device, B is the specific surface area of ​​the ternary precursor, the unit of the total amount of oxygen is L, and the unit of the specific surface area is m 2 / g.

[0095] The following is a specific description through Examples 1-6 and Comparative Examples 1-4.

[0096] Example 1

[0097] S1, reaction base solution preparation stage: NiSO4, CoSO4, MnSO4 are prepared into a mixed salt solution with a total metal concentration of 2 mol / L in a molar ratio of 60.5:10:29.5, a sodium hydroxide solution with a concentration of 10 mol / L, and an ammonia solution with a concentration of 4.5 mol / L; in a volume of 10m 3 80% clean water was added to the reactor, water was added to the transfer kettle and the thickener to the overflow port, alkali solution was added to make the pH in the reactor in the first pH range: 11.5-11.6; ammonia water was added to make the ammonia concentration in the reactor 4.5-5g / L, nitrogen with a flow rate of 150L / min was introduced into the reactor, the reactor temperature was 60°C, and the rotation speed was 350r / min.

[0098] S2, nucleation seed preparation stage: the flow rates of the mixed salt solution, alkali solution, and ammonia water are 160 L / h, 56 L / h, and 22 L / h, respectively, the median particle size of the seed obtained by the reaction is 1.65±0.05 μm, and the first pH range is maintained for 4 hours to generate a suitable number of seed crystals in the reactor;

[0099] S3. Turn on the thickener to discharge the liquid. If the discharge flow of the liquid is the same as the sum of the flow rates of the mixed salt solution, alkali solution and ammonia water, the solid content in the reactor will gradually increase.

[0100] S4, seed formation stage: the pH in the reactor is lowered to 11.0-11.1 within 10 hours. In the first pH lowering process, the flow rate of the mixed salt solution is maintained at 160 L / h for 6 hours, then the flow rate of the mixed salt solution is increased to 300 L / h and maintained for 8 hours, and finally the flow rate of the mixed salt solution is increased to 500 L / h and maintained until the particles grow to the target particle size. The alkali flow rate of the reaction process is adjusted according to the pH value, and the ammonia flow rate is adjusted according to the ammonia value; oxygen is introduced at a mixed salt solution flow rate of 300 L / h during the reaction, and thereafter the ratio of the oxygen flow rate to the material flow rate is a fixed value, that is, the oxygen flow rate changes with the flow rate of the mixed salt solution, and the ratio between the oxygen flow rate and the material flow rate is 4.5%.

[0101] S5. Maintaining the pH and ammonia content in the reactor unchanged, the particles in the reactor continue to grow, and the final solid content range is 480-500 g / L of the reaction slurry. The target precursor D 50 It is 3.3um.

[0102] The SEM image of the precursor is shown in Figure 1a-1b .like Figure 1a-1b As shown, the primary particles of the target precursor are strip-shaped, and the thickness of the primary particles is 156 nm.

[0103] The implementation steps of Examples 2-6 are the same as those of Example 1, except that the oxygen flow rate and the material flow rate are regulated. The following is a detailed description:

[0104] Example 2: The ratio of oxygen flow rate to material flow rate is a fixed value, that is, the oxygen flow rate changes with the material flow, and the ratio is 5.5%.

[0105] The SEM image of the precursor is shown in Figure 3 .like Figure 3 As shown, the primary particles on the particle surface are strip-shaped, and the average thickness of the primary particles is 133 nm.

[0106] Example 3: The ratio of oxygen flow rate to material flow rate is a fixed value, that is, the oxygen flow rate changes with the material flow, and the ratio is 6%.

[0107] The SEM image of the precursor is shown in Figure 4 .like Figure 4 As shown, the primary particles on the particle surface are strip-shaped, and the average thickness of the primary particles is 111 nm.

[0108] Example 4: The ratio of oxygen flow rate to material flow rate is a fixed value, that is, the oxygen flow rate changes with the material flow, and the ratio is 8%.

[0109] The SEM image of the precursor is shown in Figure 5 .like Figure 5 As shown, the primary particles on the particle surface are strip-shaped, and the average thickness of the primary particles is 80 nm.

[0110] Example 5: The ratio of oxygen flow rate to material flow rate is a fixed value, that is, the oxygen flow rate changes with the material flow, and the ratio is 9%. The primary particles on the particle surface are strip-shaped, and the average thickness of the primary particles is 70nm.

[0111] Example 6: The ratio of oxygen flow rate to material flow rate is a fixed value, that is, the oxygen flow rate changes with the material flow, and the ratio is 12.5%.

[0112] The primary particles on the surface of the precursor are strip-shaped, and the average thickness of the primary particles is 65 nm.

[0113] Comparative Example 1

[0114] The implementation steps are the same as those in Example 1, except that the nitrogen flow rate is maintained at 150 L / min and the oxygen flow rate is maintained at 0 L / min during the preparation process.

[0115] The SEM image of the precursor is shown in Figure 7 The SEM image of the precursor cross section is shown in Figure 8 .contrast Figure 6 , Figure 8 It can be seen that in the cross section of this comparative example 1, only the inner center position has a hole structure, and the other parts are dense structures.

[0116] Comparative Example 2

[0117] S1, reaction base solution preparation stage: NiSO4, CoSO4, MnSO4 are prepared in a molar ratio of 60:10:30 to form a mixed salt solution with a total metal concentration of 1.8 mol / L, a sodium hydroxide solution with a concentration of 10 mol / L, and an ammonia solution with a concentration of 4.5 mol / L; in a volume of 10m 3 Add 80% clean water into the reactor, add water to the transfer kettle to the overflow port, add alkali solution to make the pH in the reactor 11.4-11.5, add ammonia water to make the ammonia concentration in the reactor 2.5-3g / L, and pass nitrogen at a flow rate of 150L / min into the reactor. The reactor temperature is 60℃ and the rotation speed is 280r / min.

[0118] S2, stable output stage: the flow rate of the mixed salt solution is 300L / h, the pH in the reactor is 11.15-11.20 (both nucleation and growth occur in this pH range), the ammonia value is controlled at 2.5-3g / L, the median particle size of the precursor precipitate in the slurry is 3.5-3.6um, and the slurry generated in the reactor overflows into the unqualified aging reactor at the beginning of the reaction. When it is detected that the performance of the slurry in the reactor meets the requirements, the slurry overflows into the qualified aging reactor, and when the mass of the dry material of the generated precursor meets the requirements, the feeding of alkaline ammonia into the reactor is stopped.

[0119] The SEM image of the precursor is shown in Fig. 9 .like Fig. 9 As shown, the primary particles on the particle surface are short strips.

[0120] Comparative Example 3

[0121] Difference from Example 1: In the comparative case, oxygen was introduced at the beginning of the reaction, and the ratio of oxygen flow rate to material flow was 5%. The remaining implementation steps were the same as those in Example 1. The SEM image of the precursor is shown in Fig.10 .

[0122] Comparative Example 4

[0123] The difference from Example 1 is that the ratio of oxygen flow rate to material flow rate is a fixed value, that is, the oxygen flow rate changes with the material flow, and the ratio is 2%. The remaining implementation steps are the same as those in Example 1.

[0124] The SEM image of the precursor is shown in Fig.11 As shown, the primary particles on the particle surface are thick stripes. Fig.11 The primary particles are coarser than those in the implementation case, and the primary particles are densely packed and have fewer pores between the primary particles.

[0125] Furthermore, the parameters for introducing oxygen in Examples 1-6 are summarized in Table 1.

[0126] Table 1

[0127]

[0128] Furthermore, Examples 1-4 and Comparative Example 1 were tested using an X-ray diffractometer, and the (001) crystal plane spacing, (101) crystal plane spacing, and (100) crystal plane spacing of each Example and Comparative Example were obtained through the X-ray diffraction patterns, as shown in Table 2 for details.

[0129] Table 2

[0130] Serial number D(001) D(100) D(101) D(001) / D(101) Example 1 15.368 14.435 4.903 3.134 Example 2 16.247 15.987 5.353 3.035 Example 3 20.122 12.715 6.659 3.022 Example 4 23.272 13.334 7.601 3.062 Comparative Example 1 11.231 20.321 10.136 1.108

[0131] It can be seen that as the degree of oxidation increases, the (001) crystal plane spacing and the (101) crystal plane spacing increase synchronously. In Comparative Example 1, since no oxidation is performed, the ratio between the (001) crystal plane spacing and the (101) crystal plane spacing is lower than that of Examples 1-4.

[0132] Furthermore, the porosity of the cross-section of the precursors in Examples 1-6 and Comparative Examples 1-4 was tested using an electron scanning microscope; the specific surface area (BET) of Examples 1-6 and Comparative Examples 1-4 was tested using nitrogen adsorption-desorption. The porosity, specific surface area and other test parameters obtained by the tests are shown in Table 3.

[0133] Table 3

[0134]

[0135] Note: The BET in Table 3 was obtained by nitrogen adsorption-desorption method.

[0136] From Tables 1 to 3, it can be seen that: (1) Under the condition that the flow rate of the mixed salt solution is 160-500 L / h, when the flow rate of the mixed salt solution is increased each time, and the increase rate of the oxygen flow rate is 4%-15%, the specific surface area of ​​the precursor in Examples 1-6 gradually increases, and as the oxygen intake increases, the degree of oxidation of the precursor by oxygen increases, and the thickness of its primary particles is significantly refined. (2) As the specific surface area of ​​the precursor in Examples 1-6 increases, its tap density decreases. (3) Reference Figure 6 From the cross-sectional structure, it can be seen that under the condition of mixed salt solution flow rate of 160-500 L / h, the porosity of the precursor increases with the increase of oxidation degree. This is because the increase of oxidation degree makes the primary particles finer and the primary particles more loosely packed. (4) Comparative Example 3 and Fig.10 It can be seen that in Example 1-6, by controlling the node where oxygen is introduced, the agglomeration of the seeds caused by oxidation during the seed generation stage is avoided, thereby avoiding the problem of poor sphericity of the corresponding precursor particles, resulting in a wide particle size distribution. Therefore, the particle size distribution in Example 1-6 is narrower.

[0137] Further, based on the aforementioned method for predicting specific surface area, that is, according to the formula The specific surface areas of Examples 1-6 and Comparative Examples 1-4 were predicted, and the predicted specific surface areas are shown in Table 4.

[0138] Table 4

[0139] Serial number V(L) <![CDATA[K2]]> Predict BET error Example 1 1053 90-110 9.6-11.7 -4% to 17% Example 2 1287 90-110 11.7-14.3 -10% - to 10% Example 3 1638 90-110 14.8-18.2 -7.5% to 13.8% Example 4 1872 90-110 17.0-20.8 -10.5% to 9.5% Example 5 2340 90-110 21.3-26.0 -11.25% to 8.3% Example 6 2925 90-110 26.6-32.5 -8.3% to 12.1% Comparative Example 1 0 90-110 / / Comparative Example 2 0 90-110 / / Comparative Example 3 1335 90-110 12.1-14.8 -10.4% to 9.6% Comparative Example 4 659 90-110 5.9-7.3 -15.8% to 4.1%

[0140] Note: The error in Table 4 is based on the ratio between the difference between the predicted BET and the tested BET and the tested BET.

[0141] From the predicted specific surface area obtained by the method for predicting specific surface area provided in the embodiments of the present application in Table 4 and the test value of the specific surface area in Table 3, it can be obtained that the absolute value of the error of the predicted value obtained by the method provided in the embodiments of the present application does not exceed 17%.

[0142] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A precursor of a ternary cathode material, characterized in that: The molecular formula of the precursor of the ternary cathode material is: Ni x Co y Mn z (OH)2; where 0.4≤x≤0.8, 0.1≤y≤0.3, 0.2≤z≤0.6, x+y+z=1; The specific surface area of ​​the precursor is 10-30m 2 / g, and the particle size distribution of the precursor is less than 0.68; the particle size distribution is ; The sphericity γ of the precursor is greater than 0.96; wherein γ=4πS / L 2 , S is the area of ​​the largest cross section of the precursor, and L is the perimeter of the largest cross section; The porosity of the precursor is 5%-12%, and the cross-sectional area of ​​the pores on any cross section of the precursor is 400-2000nm 2 ; The ratio between the (001) crystal plane spacing and the (101) crystal plane spacing of the precursor is D(001) / D(101)=3C; wherein C is a preset constant, and C is 0.95-1.10; The precursor is a secondary particle composed of primary particles, the primary particles are strip-shaped, the thickness of the primary particles is 20-200 nm, and the length of the primary particles is 0.17-0.7 μm; the median particle size D of the precursor 50 3-5μm.

2. The precursor according to claim 1, characterized in that On any cross-section of the precursor, the radius of the inner circle is 1.5-2.5 μm, and the ratio of the inner circle to the outer circle is 0.4-0.7; wherein the outer circle is the circumscribed circle of the cross-section, the inner circle and the outer circle are concentric circles, and the area of ​​the largest pore on the inner circle is not greater than 1.3% of the area of ​​the smallest pore.

3. The precursor according to claim 1 or 2, characterized in that The tap density of the precursor is 1.2-2 g / cm 3 .

4. The precursor according to claim 1 or 2, characterized in that The content of sodium impurities in the precursor is less than 100 ppm, and the content of sulfur impurities is less than 1000 ppm.

5. A method for preparing a precursor of the ternary cathode material according to any one of claims 1 to 4, characterized in that: include: A mixed salt solution, an alkaline solution and a complexing agent are subjected to a coprecipitation reaction for 3-6 hours under the condition that the reaction atmosphere is nitrogen and the pH of the reaction environment is in a first pH range, to generate a first slurry including target seed crystals; wherein the mixed salt solution includes a nickel salt solution, a cobalt salt solution and a manganese salt solution; the first pH range is 11.4-11.8, and the median particle size of the seed crystals is 1.5-1.8 μm; Discharging the supernatant in the first slurry to obtain a second slurry; wherein the second slurry includes the target seed crystals; The pH value of the reaction environment is reduced to a second pH range within 12 hours, so that the target seed crystals in the second slurry continue to grow under the action of the coprecipitation reaction under the condition that the reaction atmosphere includes oxygen, to obtain an intermediate precursor; wherein the median particle size of the intermediate precursor is 2-3 μm, and the second pH range is 10.4-11.2; The intermediate precursor is allowed to continue to grow into a target precursor under the action of the coprecipitation reaction under the condition that the reaction atmosphere includes oxygen and the pH of the reaction environment is in a third pH range; wherein the third pH range is 10.4-11.2, and the median particle size of the target precursor is 3-5 μm; Before lowering the first pH range to the second pH range within 12 hours, the method further comprises: The flow rate of the mixed salt solution is increased to 300-500 L / h at an increase rate of 50%-90%; and the flow rate of oxygen is increased. The increased oxygen flow rate is determined according to the following formula: ;in, K 1 is the preset constant, K 1 4%-15%; V 1 is the increased oxygen flow rate, V 2 is the flow rate of the mixed salt solution; Before the intermediate precursor is allowed to continue to grow into a target precursor under the action of a coprecipitation reaction under the condition that the reaction atmosphere includes oxygen and the pH of the reaction environment is in a third pH range, the method further includes: The flow rate of the mixed salt solution was increased to 500-600 L / h at an increase rate of 25%-70%.

6. The method according to claim 5, characterized in that The complexing agent is ammonia water, the alkaline solution is sodium hydroxide solution, and the mixed salt solution, the alkaline solution and the complexing agent are subjected to a coprecipitation reaction for 3-6 hours under the condition that the reaction atmosphere is nitrogen and the pH value of the reaction environment is in the first pH range to generate a first slurry including target seed crystals, including: A sodium hydroxide solution with a concentration of 4-15 mol / L and an ammonia solution with a concentration of 1-8 mol / L are introduced into the reaction device, and nitrogen is introduced into the reaction device so that the ammonia content in the reaction device is 2-6 g / L, and the nitrogen content is not less than 99%; wherein the flow rate of the nitrogen is 100-200 L / min; The mixed salt solution is introduced into the reaction device at a flow rate of 160-200 L / h, so that the nickel salt, cobalt salt and manganese salt in the mixed salt solution undergo a coprecipitation reaction for 3-6 hours under the condition that the pH value is in the first pH range, to generate the target seed crystals and obtain the first slurry; wherein the concentration of the mixed salt solution is 1.2-2 mol / L.

7. The method according to claim 6, characterized in that The reaction temperature in the reaction device is 50-70° C.; the stirring speed of the rotor in the reaction device is 250 r / min-400 r / min.

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