Ternary precursor and preparation method and application thereof

Abstract

The invention relates to a ternary precursor and a preparation method and application thereof, the chemical general formula of the ternary precursor is [NiaCobMnc] 1-d-e (OH) 2 (SrSO4) d * (Sr (OH) 2) e, 0.8 < = a < 1.0, 0 < b < = 0.2, 0 < c < = 0.2, 0 < = d < = 0.0002, and 0 < = e < = 0.0002; the ternary precursor is sphere-like secondary particles formed by stacking primary particles, the primary particles comprise primary particles A and primary particles B, the thickness of the primary particles A is 50nm-150nm, the length of the primary particles A is 300nm-400nm, the thickness of the primary particles B is 20nm-40nm, the length of the primary particles B is 150nm-250nm, the number ratio of the primary particles A to the primary particles B is 0.2-5, and the number ratio of the primary particles A to the primary particles B is 0.2-5. In any two regions with the same area of the ternary precursor, the standard deviation of the content of the primary particles B is less than 1; the porosity of the ternary precursor is 10-20%, and the sulfur content is less than or equal to 600ppm. The ternary precursor is relatively large in specific surface area, good in morphology uniformity, high in tap density and low in sulfur content, so that the specific discharge capacity and the cycle performance of the lithium ion battery positive electrode material can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a ternary precursor, a preparation method thereof, and an application thereof. Background Art

[0002] The ternary precursors prepared by the existing co-precipitation method usually have low tap density and specific surface area, which will cause Li + to be difficult to enter the interior of the precursor, resulting in a low lithium intercalation amount, affecting the capacity of the cathode material, and at the same time, the content of impurity S is relatively high, especially for the ternary precursors with larger particles, resulting in low capacity and poor cycle performance of the prepared cathode material. Summary of the Invention

[0003] Based on this, it is necessary to provide a ternary precursor, a preparation method thereof, and an application thereof for the above problems. The ternary precursor has a large specific surface area, good morphological uniformity, high tap density, and low sulfur content, so as to improve the discharge specific capacity and cycle performance of the cathode material of the lithium-ion battery.

[0004] A ternary precursor, the chemical general formula of the ternary precursor is [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4) d ·(Sr(OH)2) e , where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0002, 0 ≤ e ≤ 0.0002;

[0005] The ternary precursor is a spherical secondary particle formed by stacking primary particles. Among them, the primary particles include primary particle A and primary particle B. The thickness of the primary particle A is 50 nm - 150 nm, and the length is 300 nm - 400 nm. The thickness of the primary particle B is 20 nm - 40 nm, and the length is 150 nm - 250 nm. The quantity ratio of the primary particle A to the primary particle B is 0.2 - 5, and in any two regions with the same area of the ternary precursor, the standard deviation of the content of the primary particle B is less than 1; the porosity of the ternary precursor is 10% - 20%, and the sulfur content ≤ 600 ppm.

[0006] In one embodiment, the ternary precursor further satisfies at least one of the following conditions:

[0007] (1) The aspect ratio of the primary particle A is 2 - 8;

[0008] (2) The aspect ratio of the primary particle B is 3 - 12; ​

[0009] (3) The specific surface area of the ternary precursor is 10 m 2 / g - 30 m 2 / g;

[0010] (4) The D 50 of the ternary precursor is 8 μm - 12 μm;

[0011] (5) The K 90 of the ternary precursor is 1 - 2, where K 90 = (D 90 - D 10 ) / D 50 ;

[0012] (6) The tap density of the ternary precursor is 2.0 g / cm 3 - 2.5 g / cm 3 .

[0013] In one embodiment, when d and e are not both zero, the Sr content in the primary particle A is M1, and the Sr content in the primary particle B is M2, M1 - M2 ≥ 0; or, d and e are both zero.

[0014] In the ternary precursor of the present invention, the primary particles include primary particle A and primary particle B with specific thickness and length. By controlling the quantity ratio of primary particle A and primary particle B, and in any two identical - area regions of the ternary precursor, the standard deviation of the content of primary particle B is small, so that primary particle B is evenly distributed in the gaps formed among primary particle A, and then the ternary precursor has a high tap density. Moreover, the primary particle A with larger thickness and length is beneficial to supporting the structure of the ternary precursor, which can improve the structural stability of the ternary precursor, while the primary particle B with smaller thickness and length is beneficial to fully exposing the active sites, increasing the specific surface area of the ternary precursor, facilitating the insertion and extraction of lithium ions, thereby improving the cycle performance and capacity of the cathode material; at the same time, by controlling the porosity and sulfur content of the ternary precursor, the specific surface area of the ternary precursor can be further increased, the capacity of the cathode material can be improved, and the problems of capacity decline and poor cycle performance of the cathode material caused by too high sulfur content can be effectively avoided. Therefore, the ternary precursor of the present invention has a large specific surface area, good morphology uniformity, high tap density, and low sulfur content, and can improve the discharge specific capacity and cycle performance of the cathode material of the lithium - ion battery.

[0015] A preparation method of the ternary precursor described above includes the following steps:

[0016] Using [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4)​d ·(Sr(OH)2) e Based on [Sr(OH)2], where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0002, 0 ≤ e ≤ 0.0002, a nickel salt, a cobalt salt, a manganese salt, and water are mixed to prepare a mixed salt solution;

[0017] Under a protective atmosphere, the mixed salt solution, a complexing agent solution, a precipitating agent solution, and a strontium salt solution are added to the reaction bottom liquid for reaction to obtain a ternary precursor slurry. Among them, the strontium salt solution is added to the reaction bottom liquid in an intermittent feeding manner. The intermittent feeding manner includes: continuously adding the strontium salt solution for reaction for T1 hours first, and then stopping adding the strontium salt solution and reacting for T2 hours. This is used as a cycle and repeated until the D of the ternary precursor slurry 50 reaches the target D 50 up to, where 2.5 ≤ T2 / T1 ≤ 20; and during the reaction, the D of the ternary precursor slurry is monitored regularly 50 , when the D of the ternary precursor slurry 50 is greater than the target D 50 , the pH is raised to 10.80 - 11.50. When the D of the ternary precursor slurry 50 is less than the target D 50 , the pH is lowered to 10.50 - 10.80. Such repeated operations are carried out until the D of the ternary precursor slurry 50 reaches the target D 50 up to;

[0018] The ternary precursor slurry is aged, washed, and dried to obtain a ternary precursor.

[0019] In one embodiment, 0.5 hours ≤ T1 ≤ 2 hours, 5 hours ≤ T2 ≤ 10 hours.

[0020] In one embodiment, the reaction time after each increase in pH to 10.80 - 11.50 is T3, and the reaction time after each decrease in pH to 10.50 - 10.80 is T4, where 0.2 ≤ T3 / T4 ≤ 5.

[0021] In one embodiment, in the step of mixing a nickel salt, a cobalt salt, a manganese salt, and water to prepare a mixed salt solution, at least one of the following conditions is satisfied:

[0022] (1) The total concentration of metal ions in the mixed salt solution is 1.0 mol / L - 2.5 mol / L;

[0023] (2) The nickel salt is selected from at least one of nickel sulfate, nickel chloride, and nickel nitrate;

[0024] (3) The cobalt salt is selected from at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate;

[0025] (4) The manganese salt is selected from at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0026] In one embodiment, in the step of adding the mixed salt solution, complexing agent solution, precipitating agent solution, and strontium salt solution to the reaction bottom liquid for reaction under a protective atmosphere, at least one of the following conditions is satisfied:

[0027] (1) The protective atmosphere is selected from an inert atmosphere and / or a nitrogen atmosphere;

[0028] (2) The flow rate of the mixed salt solution is 4 L / h - 8 L / h;

[0029] (3) The concentration of the complexing agent solution is 1 mol / L - 15 mol / L, and the complexing agent solution is selected from at least one of an ammonia water solution and sodium citrate;

[0030] (4) The concentration of the precipitating agent solution is 10 mol / L - 15 mol / L, and the precipitating agent solution is selected from at least one of a sodium hydroxide solution and sodium carbonate;

[0031] (5) The flow rate of the strontium salt solution during feeding is 0.01 L / h - 3 L / h;

[0032] (6) The concentration of the strontium salt solution is 0.01 mol / L - 3.0 mol / L;

[0033] (7) The strontium salt solution is selected from at least one of strontium chloride solution, strontium nitrate, and strontium acetate;

[0034] (8) The target D 50 is 8 μm - 12 μm;

[0035] (9) The temperature of the reaction bottom liquid is 40°C - 70°C, the ammonia value is 1 g / L - 10 g / L, and the pH is 11.0 - 12.0.

[0036] In the preparation method of the present invention, by repeatedly adjusting the pH value during the reaction process, and at the same time adopting an intermittent feeding method for feeding the strontium salt solution, and controlling the ratio of the non-feeding reaction time to the feeding reaction time T2 / T1 of the strontium salt solution in each cycle. During the reaction process, due to the difference in the solubility products of strontium ions, nickel ions, cobalt ions, and manganese ions by several orders of magnitude, the overall reaction is a heterogeneous reaction, inducing the formation of two different types of primary particles with a specific quantitative ratio on the surface of the ternary precursor, making the ternary precursor have a high tap density. Moreover, in this process, by controlling the ratio of T2 / T1, the content of strontium ions in the reaction system can be effectively controlled within a suitable range. During the reaction process, strontium exists in the form of strontium sulfate and / or strontium hydroxide, and compared with nickel cobalt manganese hydroxide, strontium sulfate and strontium hydroxide have a higher surface energy, so that they adsorb on the surface of the larger-crystallized nickel cobalt manganese hydroxide and the combination is not firm. Therefore, during the washing process, strontium sulfate and / or strontium hydroxide are easily washed away, leaving pores at the original position of strontium sulfate / strontium hydroxide, thereby increasing the porosity of the ternary precursor, further increasing the specific surface area of the ternary precursor, and effectively removing the sulfur content in the ternary precursor. In addition, in the preparation method of the present invention, the strontium salt solution serves both as a pore-forming agent and a desulfurizing agent, reducing the cost, and the operation is simple, suitable for large-scale production.

[0037] A positive electrode material prepared by using the above-mentioned ternary precursor.

[0038] A positive electrode sheet prepared by using the above-mentioned positive electrode material.

[0039] A lithium-ion battery prepared by using the above-mentioned positive electrode sheet. Description of the Drawings

[0040] Figure 1 It is the scanning electron microscope image and partial enlarged view of the ternary precursor prepared in Example 1 of the present invention, wherein, A is the scanning electron microscope image and B is the partial enlarged view;

[0041] Figure 2 It is the cross-sectional electron microscope image of the ternary precursor prepared in Example 1 of the present invention;

[0042] Figure 3 It is the scanning electron microscope image and cross-sectional view of the ternary precursor prepared in Comparative Example 1 of the present invention, wherein, A is the scanning electron microscope image and B is the cross-sectional view;

[0043] Figure 4 It is the scanning electron microscope image and partial enlarged view of the ternary precursor prepared in Comparative Example 2 of the present invention, wherein, A is the scanning electron microscope image and B is the partial enlarged view. Detailed Embodiments

[0044] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, these embodiments or examples are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs.

[0046] The ternary precursor provided by the present invention, the chemical general formula of the ternary precursor is [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4) d ·(Sr(OH)2) e , where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0001, 0 ≤ e ≤ 0.0001; the ternary precursor is a spherical secondary particle formed by the accumulation of primary particles, where the primary particles include primary particle A and primary particle B, the thickness of the primary particle A is 50nm - 150nm, the length is 300nm - 400nm, the thickness of the primary particle B is 20nm - 40nm, the length is 150nm - 250nm, the quantity ratio of the primary particle A and the primary particle B is 0.2 - 5, and in any two regions with the same area of the ternary precursor, the standard deviation of the content of the primary particle B is less than 1, preferably less than 0.7; the porosity of the ternary precursor is 10% - 20%, and the sulfur content ≤ 600ppm.

[0047] It can be understood that the surface of the ternary precursor is formed by the interlaced accumulation of primary particle A and primary particle B, and the primary particle B grows uniformly in the gaps formed between the primary particle A.

[0048] Optionally, the aspect ratio of the primary particle A is 2 - 8; the aspect ratio of the primary particle B is 3 - 12; thus set, by regulating the aspect ratios of the primary particle A and the primary particle B, the tap density, sphericity and porosity of the ternary precursor can be better regulated, which is beneficial to improving the tap density and specific surface area of the ternary precursor while having a high sphericity, effectively avoiding the situation of cracked spheres due to excessive local stress on the surface of the ternary precursor.

[0049] Optionally, the specific surface area of the ternary precursor is 10m 2 / g - 30m 2 ​ / g. Such a setting makes the ternary precursor have a large specific surface area, which is beneficial to improving the specific capacity and cycling performance of the cathode material.

[0050] Optionally, the D of the ternary precursor 50 is 8 μm - 12 μm. Such a setting is beneficial to making the ternary precursor have a large specific surface area while having high structural stability, and thus is beneficial to improving the specific capacity and cycling performance of the cathode material.

[0051] Optionally, the K of the ternary precursor 90 is 1 - 2, where K 90 =(D 90 -D 10 ) / D 50 . Such a setting is beneficial to making the ternary precursor have good morphological uniformity.

[0052] It should be noted that in the present invention, a laser particle size analyzer is used to measure the particle sizes D 50 , D 90 and D 10 of the ternary precursor, and at the same time, according to the calculation formula K 90 =(D 90 -D 10 ) / D 50 , the particle size distribution distance K 90 of the ternary precursor is calculated.

[0053] Optionally, the tap density of the ternary precursor is 2.0 g / cm 3 -2.5 g / cm 3 . Such a setting makes the ternary precursor have a high tap density, which is beneficial to improving the overall energy density of the battery.

[0054] At the same time, according to the chemical general formula of the ternary precursor and the values of the parameters a, b, c, d, and e, it can be known that the ternary precursor of the present invention belongs to a high-nickel ternary precursor, and according to the values of d and e, ternary precursors with different chemical general formulas can be obtained, specifically as follows:

[0055] When d and e are not both zero at the same time, the molecular general formula has three forms. The first one: when d = 0, the chemical general formula of the ternary precursor is [Ni a Co b Mn c 1-e (OH)2·(Sr(OH)2) e , where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ e ≤ 0.0002. At this time, the ternary precursor is composed of two phases, nickel-cobalt-manganese hydroxide and strontium hydroxide; the second one: when e = 0, the chemical general formula of the ternary precursor is [Ni​a Co b Mn c 1-d (OH)2·(SrSO4) d , wherein, 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0002. At this time, the ternary precursor consists of two phases, nickel cobalt manganese hydroxide and strontium sulfate; The third: when 0 < d ≤ 0.0002 and 0 < e ≤ 0.0002, the general chemical formula of the ternary precursor is [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4) d ·(Sr(OH)2) e , wherein, 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 < d ≤ 0.0002, 0 < e ≤ 0.0002. At this time, the ternary precursor consists of three phases, nickel cobalt manganese hydroxide, strontium hydroxide and strontium sulfate.

[0056] When both d and e are zero, that is, when d = 0 and e = 0, the general chemical formula of the ternary precursor is Ni a Co b Mn c (OH)2, wherein, 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2. At this time, the ternary precursor consists of a single phase of nickel cobalt manganese hydroxide.

[0057] Optionally, when d and e are not both zero, the Sr content in the primary particle A is M1, and the Sr content in the primary particle B is M2, and M1 - M2 ≥ 0. With such a setting, it is beneficial to improve the stability of the cathode material.

[0058] In the present invention, the primary particles of the ternary precursor include primary particle A and primary particle B with specific thickness and length. At the same time, the number ratio of primary particle A and primary particle B is controlled, and in any two regions with the same area of the ternary precursor, the standard deviation of the content of primary particle B is small, so that primary particle B is evenly distributed in the gaps formed between primary particle A, and then the ternary precursor has a high tap density. Moreover, the primary particle A with larger thickness and length is beneficial to supporting the structure of the ternary precursor, can improve the structural stability of the ternary precursor, and avoid the structural collapse of the ternary precursor during the sintering process. While the primary particle B with smaller thickness and length is beneficial to fully expose the active sites, increase the specific surface area of the ternary precursor, facilitate the insertion and extraction of lithium ions, and thus improve the cycle performance and capacity of the cathode material.

[0059] ​​Meanwhile, by controlling the porosity and sulfur content of the ternary precursor, the specific surface area of the ternary precursor can be further increased, the capacity of the cathode material can be improved, and at the same time, the problems of capacity decline and poor cycling performance of the cathode material caused by excessive sulfur content can be effectively avoided.

[0060] In addition, since the secondary particles of the ternary precursor are spherical-like structures, after detection, not only the morphology has good uniformity, but also the sphericity is good.

[0061] Therefore, the ternary precursor of the present invention has a large specific surface area, good morphological uniformity, high tap density, and low sulfur content, and can improve the discharge specific capacity and cycling performance of the cathode material for lithium-ion batteries.

[0062] Meanwhile, the present invention also provides a preparation method of the ternary precursor, including the following steps:

[0063] Taking [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4) d ·(Sr(OH)2) e as a reference, where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0002, 0 ≤ e ≤ 0.0002, mixing nickel salt, cobalt salt, manganese salt and water to prepare a mixed salt solution;

[0064] Under a protective atmosphere, adding the mixed salt solution, complexing agent solution, precipitating agent solution and strontium salt solution to the reaction bottom liquid for reaction to obtain a ternary precursor slurry, where the strontium salt solution is added to the reaction bottom liquid in an intermittent feeding manner, and the intermittent feeding manner includes: continuously adding the strontium salt solution for reaction for T1 hours first, then stopping adding the strontium salt solution and reacting for T2 hours, and repeating this operation as a cycle until the D 50 of the ternary precursor slurry reaches the target D 50 ; 2.5 ≤ T2 / T1 ≤ 20; and during the reaction, regularly monitor the D 50 of the ternary precursor slurry, when the D 50 of the ternary precursor slurry is greater than the target D 50 , raise the pH to 10.80 - 11.50, when the D 50 of the ternary precursor slurry is less than the target D 50 , lower the pH to 10.50 - 10.80, and repeat the operation until the D 50 of the ternary precursor slurry reaches the target D 50 ;

[0065] ​The ternary precursor slurry is aged, washed, and dried to obtain a ternary precursor.

[0066] In the preparation method of the present invention, during the reaction, the D of the ternary precursor slurry is regularly monitored 50 , and based on the D of the ternary precursor slurry 50 and the target D 50 relationship, the pH value of the reaction system is repeatedly adjusted. At the same time, a strontium salt solution is added to the reaction system in an intermittent manner to control the content of strontium during the reaction. During the reaction, due to the solubility product of strontium ions differing from those of nickel ions, cobalt ions, and manganese ions by 6 - 11 orders of magnitude, the overall reaction is a heterogeneous reaction, that is, strontium sulfate / strontium hydroxide and nickel cobalt manganese hydroxide do not exist in the form of coprecipitation, inducing the growth of two types of primary particles on the surface of the ternary precursor, specifically as follows: when the pH is low, the hydroxide concentration in the reaction system is low, and Sr in the reaction system 2+ mainly precipitates in the form of SrSO4. Due to the high surface energy of SrSO4, it can induce the formation of primary particles with smaller thickness and length, that is, primary particle B, and the thickness is 20nm - 40nm, the length is 150nm - 250nm, and the aspect ratio is 3 - 12. The primary particles of this size are conducive to fully exposing the active sites, increasing the specific surface area of the ternary precursor, promoting the insertion and extraction of lithium ions, and then being beneficial to increasing the specific capacity of the cathode material; when the pH is high, the hydroxide concentration in the reaction system is high, and Sr in the reaction system 2+ mainly precipitates in the form of Sr(OH)2. Compared with SrSO4, Sr(OH)2 has a lower surface energy, which is conducive to the formation of primary particles with larger thickness and length, that is, primary particle A, and the thickness is 50nm - 150nm, the length is 300nm - 400nm, and the aspect ratio is 2 - 8. The primary particles of this size can effectively support the structure of the ternary precursor, improve the structural stability of the ternary precursor, avoid structural collapse during the sintering process, and then improve the structural stability and cycling performance of the cathode material.

[0067] At the same time, by controlling the ratio of the non - feeding reaction time to the feeding reaction time T2 / T1 of the strontium salt solution in each cycle, the feeding timing of the strontium salt solution is precisely controlled, which can better control the content of strontium in the reaction system, and then regulate the number of primary particle A and primary particle B, control the number ratio of primary particle A to the primary particle B to be 0.2 - 5, so that primary particle B is distributed in the gaps formed between the primary particle A, and in any two regions with the same area of the ternary precursor, the standard deviation of the content of primary particle B is less than 1, forming spherical secondary particles with primary particle B uniformly distributed on the surface, thereby enabling the ternary precursor to have a high tap density.

[0068] Moreover, by controlling the ratio of T2 / T1, the content of strontium ions in the reaction system can be effectively controlled within a suitable range and is lower than the contents of nickel ions, cobalt ions, and manganese ions in the reaction system, ensuring the formation of a ternary precursor mainly composed of nickel-cobalt-manganese hydroxide. Meanwhile, during the reaction process, since strontium exists in the form of strontium sulfate and / or strontium hydroxide, compared with nickel-cobalt-manganese hydroxide, strontium sulfate and strontium hydroxide have higher surface energies. Therefore, strontium sulfate and strontium hydroxide are easily adsorbed on the surface of the relatively large-crystallized nickel-cobalt-manganese hydroxide, and the combination is not firm. Thus, during the washing process, strontium sulfate and / or strontium hydroxide are easily washed away, leaving pores at the original positions of strontium sulfate / strontium hydroxide, and the pores are evenly distributed, thereby increasing the porosity of the ternary precursor, further increasing the specific surface area of the ternary precursor, and effectively removing the sulfur content in the ternary precursor.

[0069] In addition, it should be noted that by repeatedly adjusting the pH of the reaction system, during the reaction process, at a higher pH, the ternary precursor slurry tends to nucleate alone, and at a lower pH, it tends to grow on the surface of the ternary precursor. Therefore, when the D 50 of the ternary precursor slurry is greater than the target D 50 , the pH is increased to generate new nuclei, and the D 50 of the ternary precursor slurry will decrease accordingly; when the D 50 of the ternary precursor slurry is less than the target D 50 , the pH is decreased. At this time, the D 50 of the ternary precursor slurry will increase accordingly, so that a stable D 50 output can be achieved by regulating the pH, thereby obtaining a ternary material precursor with good morphological uniformity and high tap density, which is beneficial to increasing the energy density of the cathode material per unit volume.

[0070] Therefore, in the preparation method of the present invention, by repeatedly adjusting the pH value during the reaction process, and simultaneously adopting an intermittent feeding method for feeding the strontium salt solution, and controlling the ratio of the non-feeding reaction time to the feeding reaction time T2 / T1 of the strontium salt solution in each cycle, under the synergistic effect, the morphologies, quantity ratios, and distributions of the two types of primary particles on the surface of the ternary precursor can be effectively regulated, thereby optimizing the structural properties of the ternary precursor, enhancing the specific surface area and tap density of the ternary precursor, reducing the sulfur impurity content, and having good morphological uniformity and high sphericity.

[0071] It should be noted that in the preparation method of the present invention, during the reaction process, by controlling the ratio of T2 / T1, the content of strontium ions in the reaction process is relatively low. After washing, the content of strontium in the obtained ternary precursor is very low, even zero. Moreover, if the ternary precursor contains strontium element, then the content of strontium in the primary particle A in the ternary precursor is greater than that in the primary particle B. This is because during the reaction process, by repeatedly adjusting the pH value of the reaction system, primary particle A is formed at high pH, and Sr mainly precipitates in the form of Sr(OH)2, while primary particle B is formed at low pH, and Sr mainly precipitates in the form of SrSO4. Compared with SrSO4, Sr(OH)2 is more stable in the reaction system. Therefore, after washing, the content of strontium in primary particle A is greater than that in primary particle B; if the ternary precursor does not contain strontium element, then the content of strontium in primary particle A is equal to that in primary particle B. That is, in the ternary precursor of the present invention, when d and e are not both zero at the same time, the content of Sr in the primary particle A is M1, and the content of Sr in the primary particle B is M2, and M1 - M2 ≥ 0.

[0072] It can be seen from this that in the present invention, the role of adding the strontium salt solution is not to dope strontium element in the ternary precursor to improve the comprehensive performance of the cathode material, but to use the strontium salt solution as both a pore-forming agent and a desulfurizing agent, so as to improve the porosity of the ternary precursor, increase the specific surface area of the ternary precursor, and at the same time reduce the content of sulfur impurities, thereby improving the discharge specific capacity and cycle performance of the cathode material. Therefore, the addition of the strontium salt solution in the present invention not only reduces the cost, but also has simple operation and is suitable for large-scale production.

[0073] Moreover, since strontium sulfate and nickel cobalt manganese hydroxide are in two phases, only a small amount of detergent is needed to remove them during washing, and the desulfurization effect is good. Usually, S ≤ 600 ppm, further reducing the production cost.

[0074] Considering the influence of the feeding reaction time T1 and the non-feeding reaction time T2 of the strontium salt solution in each cycle on the number and distribution uniformity of the primary particles A and B, in step S2, 0.5 h ≤ T1 ≤ 2 h, 5 h ≤ T2 ≤ 10 h. It can be understood that after continuously adding the strontium salt solution and reacting for 0.5 h - 2 h, then stop adding the strontium salt solution and react for 5 h - 10 h, and use this as a cycle to operate repeatedly until the D of the ternary precursor slurry 50 reaches the target D 50Up to this point. With such a setting, it is possible to better control the content of Sr during the reaction, and it is possible to better coordinate with the change of the pH value in the reaction system to form spherical secondary particles formed by the interlaced stacking of primary particle A and primary particle B. The ratio of the number of primary particle A to primary particle B is controlled to be 0.2 - 5, and in any two regions with the same area of the ternary precursor, the standard deviation of the content of primary particle B is small, so as to form secondary particles with primary particle B evenly distributed on the surface. After washing, a ternary precursor with uniform internal pore distribution and high porosity is formed, thereby increasing the specific surface area of the ternary precursor, and further improving the capacity and cycle performance of the cathode material.

[0075] Optionally, the reaction time after each pH increase to 10.80 - 11.50 is T3, and the reaction time after each pH decrease to 10.50 - 10.80 is T4, and 0.2 ≤ T3 / T4 ≤ 5. With such a setting, by regulating the ratio of T3 / T4, it is possible to coordinate the ratio of the non-feeding reaction time to the feeding reaction time T2 / T1 of the strontium salt solution in each cycle to better control the number of primary particle A and primary particle B, and better improve the tap density of the ternary precursor.

[0076] Optionally, the total concentration of metal ions in the mixed salt solution is 1.0 mol / L - 2.5 mol / L; the concentration of the strontium salt solution is 0.01 mol / L - 1.0 mol / L; the concentration of the complexing agent solution is 1 mol / L - 15 mol / L; the concentration of the precipitant solution is 10 mol / L - 15 mol / L. With such a setting, it is beneficial for sufficient reaction between each component.

[0077] Optionally, the flow rate of the mixed salt solution is 4 L / h - 8 L / h. With such a setting, it is beneficial to regulate the content of the mixed salt in the reaction system to enable sufficient coprecipitation reaction.

[0078] Optionally, the flow rate of the strontium salt solution during feeding is 0.01 L / h - 3 L / h. With such a setting, it is beneficial to regulate the content of the strontium salt solution in the reaction system to enable sufficient reaction.

[0079] Optionally, the nickel salt is selected from at least one of nickel sulfate, nickel chloride, and nickel nitrate.

[0080] Optionally, the cobalt salt is selected from at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate.

[0081] Optionally, the manganese salt is selected from at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0082] Optionally, the strontium salt solution is selected from at least one of strontium chloride solution, strontium nitrate, and strontium acetate.

[0083] Optionally, the complexing agent solution is selected from at least one of ammonia water solution and sodium citrate, preferably ammonia water solution.

[0084] Optionally, the precipitating agent solution is selected from at least one of sodium hydroxide solution and sodium carbonate, preferably sodium hydroxide solution.

[0085] Optionally, the target D 50 is 8 μm - 12 μm; with such a setting, a ternary precursor with D 50 being 8 μm - 12 μm can be obtained.

[0086] Optionally, the protective atmosphere is selected from an inert atmosphere and / or a nitrogen atmosphere, preferably a nitrogen atmosphere. Under the protective atmosphere, it is beneficial for the reactants to react without introducing impurities and without generating impurity molecules, ensuring a relatively high-purity ternary precursor is obtained.

[0087] In one embodiment, the flow rate of the protective gas forming the protective atmosphere is 0.1 m 3 / h - 1.0 m 3 / h. With such a setting, it can ensure that the entire reaction process proceeds in an environment of the protective atmosphere.

[0088] In the present invention, the reaction bottom liquid is obtained by mixing a complexing agent, a precipitating agent, and water. Specifically, deionized water is filled into the reactor, and at the same time, a protective gas is introduced, and then the complexing agent and the precipitating agent are added to form the reaction bottom liquid. Among them, the protective gas is preferably nitrogen. When the complexing agent is ammonia water, the temperature of the reaction bottom liquid is 40°C - 70°C, the ammonia value is 1 g / L - 10 g / L, and the pH is 11.0 - 12.0.

[0089] In one embodiment, in the step of adding the complexing agent and the precipitating agent to form the reaction bottom liquid, the stirring speed is 300 rpm - 900 rpm. With such a setting, the complexing agent, the precipitating agent, and water can be mixed evenly.

[0090] In one embodiment, in the step of adding the mixed salt solution, the complexing agent solution, the precipitating agent solution, and the strontium salt solution to the reaction bottom liquid for reaction, the ammonia value in the reaction system can be controlled to be 1 g / L - 10 g / L by adjusting the flow rate of the complexing agent solution, such as the flow rate of ammonia water.

[0091] In the present invention, in the washing step, the washing liquid is obtained by mixing a detergent and a solvent. Among them, the detergent is selected from at least one of water, inorganic base, and sodium citrate, preferably inorganic base and sodium citrate. Among them, the inorganic base is preferably sodium hydroxide or sodium carbonate.

[0092] Specifically, when the detergent is selected from inorganic bases and sodium citrate, the washing solution is obtained by mixing an inorganic base and sodium citrate. At this time, the washing solution includes the inorganic base and sodium citrate, wherein the molar ratio of the inorganic base to the sodium citrate is 1:1 - 15:1. With such a setting, sodium citrate can undergo a complexation reaction with Sr in strontium sulfate or strontium hydroxide, dissolving the precipitate of strontium sulfate or strontium hydroxide and leaving pores in its original position. Therefore, when washing, using sodium citrate as the detergent can cooperate with the inorganic base to better remove strontium sulfate or strontium hydroxide inside the ternary precursor, so as to obtain a higher porosity and specific surface area.

[0093] In one embodiment, after drying, it also includes processes such as sieving and iron removal, and finally a ternary precursor product is obtained. The specific steps can be carried out by conventional processes, so they will not be elaborated here.

[0094] In addition, the present invention also provides a cathode material prepared by using the above-mentioned ternary precursor. This cathode material has excellent discharge specific capacity and cycling performance.

[0095] A cathode sheet prepared by using the above-mentioned cathode material.

[0096] And a lithium-ion battery prepared by using the above-mentioned cathode sheet. This lithium-ion battery has excellent discharge specific capacity and cycling performance.

[0097] Hereinafter, the ternary precursor, its preparation method and application will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0098] Example 1

[0099] Mix nickel sulfate, cobalt sulfate, manganese sulfate and deionized water evenly to prepare a mixed salt solution. Among them, the total concentration of metal ions in the mixed salt solution is 1.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 94:4.5:1.5; prepare a strontium chloride solution with a concentration of 1.2 mol / L from strontium chloride hexahydrate; prepare an ammonia water solution with a concentration of 9.8 mol / L from ammonia water and deionized water; prepare a sodium hydroxide solution with a concentration of 11 mol / L from sodium hydroxide and water.

[0100] Fill a 100 L clean reaction kettle with deionized water, control the temperature at 65 °C, control the stirring speed at 650 rpm, and at the same time continuously introduce a flow rate of 0.3 m 3Nitrogen at / h, and then ammonia water solution and sodium hydroxide solution are introduced into the reaction kettle to form a reaction bottom liquid. Among them, the ammonia value of the reaction bottom liquid is 3 g / L and the pH is 11.60.

[0101] The above-mentioned mixed salt solution, ammonia water solution, sodium hydroxide solution and strontium chloride solution are added into the reaction kettle through a precision constant flow pump for reaction to obtain a ternary precursor slurry. Among them, the flow rate of the mixed salt solution is 6 L / h. The intermittent feeding method of the strontium chloride solution includes: continuously adding the strontium chloride solution for reaction for 2 h first, then stopping adding the strontium chloride solution and reacting for 10 h, and repeating this operation as a cycle. Among them, the flow rate of the strontium chloride solution is 1.5 L / h. At the same time, the flow rate of the ammonia water solution is adjusted so that the ammonia value in the reaction kettle is about 3 g / L, and samples are taken every 2 h during the reaction to measure the D of the ternary precursor 50 , and the D of the initially prepared ternary precursor slurry 50 is very small. Starting from D 50 close to 0 μm and growing. When maintaining the pH at 10.5 in the early stage, the D of the ternary precursor slurry 50 grows to 7 μm. Open the overflow valve and continuously discharge the material in a continuous overflow manner, and slowly increase the pH. When the D of the ternary precursor slurry 50 grows to 11 μm, increase the pH to 10.90 and maintain it for 5 h. When the D of the ternary precursor slurry 50 drops to 9 μm, lower the pH to 10.70 and maintain it for 5 h. By repeatedly adjusting the pH until the D of the ternary precursor slurry 50 is stable at 10 μm.

[0102] The ternary precursor slurry is pumped into the aging kettle, then introduced into a centrifuge, and 10 mol / L sodium hydroxide and 1 mol / L sodium citrate are used as washing liquids for centrifugal washing for 20 min and hot water centrifugal washing for 40 min. Then it is placed in a blast drying oven at 130 °C for drying for 20 h. Finally, it is sieved through a 325-mesh sieve, and after iron removal, a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.9998 (OH)2·(SrSO4) 0.00008 ·(Sr(OH)2) 0.00012 is obtained.

[0103] It can be seen from Figure 1 that the ternary precursor of Example 1 is a spherical secondary particle formed by the interlaced stacking of two types of primary particles, that is, a spherical secondary particle formed by the interlaced stacking of primary particle A and primary particle B. Among them, primary particle A and primary particle B are evenly distributed and have good sphericity. At the same time, from Figure 2 ​It can be seen that the internal pore distribution of the ternary precursor in Example 1 is uniform and the porosity is high, indicating that strontium chloride can act as a pore-forming agent to increase the specific surface area by increasing the internal pores of the ternary precursor.

[0104] Example 2

[0105] Mix nickel sulfate, cobalt sulfate, manganese sulfate and deionized water evenly to prepare a mixed salt solution. Among them, the total concentration of metal ions in the mixed salt solution is 2.5 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 94:4.5:1.5; prepare a strontium chloride solution with a concentration of 3.0 mol / L from strontium chloride hexahydrate; prepare an ammonia water solution with a concentration of 15 mol / L from ammonia water and deionized water; prepare a sodium hydroxide solution with a concentration of 15 mol / L from sodium hydroxide and water.

[0106] Fill a 100 L clean reactor with deionized water, control the temperature at 65 °C, control the stirring speed at 650 rpm, and continuously introduce nitrogen with a flow rate of 0.3 m 3 / h into the reactor, and then introduce the ammonia water solution and the sodium hydroxide solution into the reactor to form a reaction bottom liquid. Among them, the ammonia value of the reaction bottom liquid is 10 g / L and the pH is 12.0.

[0107] Add the above-mentioned mixed salt solution, ammonia water solution, sodium hydroxide solution and strontium chloride solution into the reactor through a precision constant flow pump for reaction to obtain a ternary precursor slurry. Among them, the flow rate of the mixed salt solution is 8 L / h. The intermittent feeding method of the strontium chloride solution includes: continuously adding the strontium chloride solution for reaction for 2 h first, then stopping adding the strontium chloride solution and reacting for 10 h, and repeating this operation as a cycle. Among them, the flow rate of the strontium chloride solution is 3 L / h. At the same time, adjust the flow rate of the ammonia water solution so that the ammonia value in the reactor is about 10 g / L, and sample and measure the D of the ternary precursor every 2 h during the reaction 50 The D of the initially prepared ternary precursor slurry 50 is very small, starting to grow from D 50 close to 0 μm. When maintaining a pH of 10.60 in the early stage, the D of the ternary precursor slurry 50 grows to 6.0 μm. Open the overflow valve and continuously discharge the material in a continuous overflow manner, and slowly increase the pH. When the D of the ternary precursor slurry 50 grows to 12 μm, increase the pH to 11.50 and maintain it for 5 h. When the D of the ternary precursor slurry 50 drops to 8 μm, lower the pH to 10.50 and maintain it for 1 h. By repeatedly adjusting the pH until the D of the ternary precursor slurry 50 is stable at 10 μm.

[0108] The ternary precursor slurry is pumped into an aging kettle and then introduced into a centrifuge. Using 15 mol / L sodium hydroxide and 1 mol / L sodium citrate as washing solutions, it is centrifugally washed for 20 min and then centrifugally washed with hot water for 40 min. Then it is placed in a blast drying oven at 130 °C and dried for 20 h. Finally, it is sieved through a 325-mesh sieve. After removing iron, a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.9998 (OH)2·(SrSO4) 0.00016 ·(Sr(OH)2) 0.00004 is obtained.

[0109] Example 3

[0110] Nickel sulfate, cobalt sulfate, manganese sulfate and deionized water are mixed evenly to prepare a mixed salt solution. Among them, the total concentration of metal ions in the mixed salt solution is 1.0 mol / L, and the molar ratio of nickel ions, cobalt ions and manganese ions is 94:4.5:1.5. Strontium chloride hexahydrate is prepared into a strontium chloride solution with a concentration of 0.01 mol / L. Ammonia water and deionized water are prepared into an ammonia water solution with a concentration of 1.0 mol / L. Sodium hydroxide and water are prepared into a sodium hydroxide solution with a concentration of 10 mol / L.

[0111] 100 L of clean reactor is filled with deionized water, the temperature is controlled at 65 °C, and the stirring speed is controlled at 650 rpm. At the same time, nitrogen with a flow rate of 0.3 m 3 / h is continuously introduced into the reactor. Then the ammonia water solution and the sodium hydroxide solution are introduced into the reactor to form a reaction bottom liquid. Among them, the ammonia value of the reaction bottom liquid is 1 g / L and the pH is 11.0.

[0112] The above-mentioned mixed salt solution, ammonia water solution, sodium hydroxide solution and strontium chloride solution are added into the reactor through a precision constant flow pump for reaction to obtain a ternary precursor slurry. Among them, the flow rate of the mixed salt solution is 4 L / h. The intermittent feeding method of the strontium chloride solution includes: continuously adding the strontium chloride solution for reaction for 0.5 h first, then stopping adding the strontium chloride solution and reacting for 5 h. This is used as a cycle and repeated. Among them, the flow rate of the strontium chloride solution is 0.01 L / h. At the same time, the flow rate of the ammonia water solution is adjusted so that the ammonia value in the reactor is about 10 g / L. And during the reaction, samples are taken every 2 h to measure the D 50 of the ternary precursor. The D 50 of the initially prepared ternary precursor slurry is very small. Starting from D 50 close to 0 μm, it begins to grow. When maintaining the pH at 10.60 in the early stage, the D 50 ​Grow to 6.0 μm, open the overflow valve, continuously discharge the material in a continuous overflow manner, and slowly increase the pH. When the D of the ternary precursor slurry 50 grows to 12 μm, increase the pH to 11.50 and maintain it for 1 h. When the D of the ternary precursor slurry 50 drops to 10 μm, lower the pH to 10.5 and maintain it for 5 h. By repeatedly adjusting the pH until the D of the ternary precursor slurry 50 is stable at 11 μm.

[0113] Pump the ternary precursor slurry into the aging kettle, then introduce it into the centrifuge. Use 1 mol / L sodium hydroxide and 1 mol / L sodium citrate as the washing liquid, centrifugally wash for 20 min, centrifugally wash with hot water for 40 min, then place it in a blast drying oven at 130 °C and dry for 20 h. Finally, sieve it through a 325-mesh sieve. After removing iron, obtain a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.99977 (OH)2·(SrSO4) 0.00009 ·(Sr(OH)2) 0.00014 .

[0114] Example 4

[0115] Compared with Example 1, Example 4 is only different in that the intermittent feeding method of the strontium chloride solution includes: continuously adding the strontium chloride solution and reacting for 2 h first, then stopping adding the strontium chloride solution and reacting for 20 h, and repeating this operation as a cycle; the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.99994 (OH)2·(SrSO4) 0.000024 ·(Sr(OH)2) 0.000036 is obtained.

[0116] Example 5

[0117] Compared with Example 1, Example 5 is only different in that the intermittent feeding method of the strontium chloride solution includes: continuously adding the strontium chloride solution and reacting for 3 h first, then stopping adding the strontium chloride solution and reacting for 9 h, and repeating this operation as a cycle; the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.9999 (OH)2·(SrSO4) 0.00005 ·(Sr(OH)2) 0.00005 is obtained.

[0118] Example 6​​​

[0119] Example 6 is different from Example 1 only in that when the D of the ternary precursor slurry 50 grows to 11.0 μm, the pH is raised to 10.90 and maintained for 1 h. When the D of the ternary precursor slurry 50 drops to 9.0 μm, the pH is lowered to 10.70 and maintained for 10 h; the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.9999 (OH)2·(SrSO4) 0.00009 ·(Sr(OH)2) 0.00001 is obtained.

[0120] Example 7

[0121] Example 7 is different from Example 1 only in that when the D of the ternary precursor slurry 50 grows to 11 μm, the pH is raised to 10.90 and maintained for 6 h. When the D of the ternary precursor slurry 50 drops to 9.0 μm, the pH is lowered to 10.70 and maintained for 1 h; the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.9999 (OH)2·(SrSO4) 0.00003 ·(Sr(OH)2) 0.00007 is obtained.

[0122] Example 8

[0123] Example 8 is different from Example 1 only in that the concentration of the strontium chloride solution is 0.005 mol / L, and the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.999952 (OH)2·(SrSO4) 0.00002304 ·(Sr(OH)2) 0.00002496 is obtained.

[0124] Example 9

[0125] Example 9 is different from Example 1 only in that the concentration of the strontium chloride solution is 4 mol / L, and the other conditions are the same, and [Ni 0.94 Co 0.045 Mn 0.015 0.9997 (OH)2·(SrSO4) 0.0001 ·(Sr(OH)2)​​​​0.0002 ternary precursor

[0126] Example 10

[0127] Compared with Example 1, Example 10 is only different in that 4 mol / L sodium hydroxide and 5 mol / L sodium citrate are used as the washing solution, and the rest of the conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.999795 (OH)2·(SrSO4) 0.000035 ·(Sr(OH)2) 0.00017 is obtained

[0128] Example 11

[0129] Compared with Example 1, Example 11 is only different in that 10 mol / L sodium hydroxide and 0.5 mol / L sodium citrate are used as the washing solution, and the rest of the conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.999765 (OH)2·(SrSO4) 0.000045 ·(Sr(OH)2) 0.00019 is obtained

[0130] Example 12

[0131] Compared with Example 1, Example 12 is only different in that 10 mol / L sodium hydroxide is used as the washing solution, and the rest of the conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.99962 (OH)2·(SrSO4) 0.0002 ·(Sr(OH)2) 0.00018 is obtained

[0132] Comparative Example 1

[0133] Compared with Example 1, Comparative Example 1 is only different in that it does not contain strontium chloride solution, that is, a mixed salt solution, an ammonia water solution, a sodium hydroxide solution and a reaction bottom solution are prepared according to the method of Example 1, wherein the molar ratio of nickel ions, cobalt ions and manganese ions is 94:4.5:1.5; the above-mentioned mixed salt solution, ammonia water solution and sodium hydroxide solution are added into the reaction kettle through a precision constant current pump for reaction; the rest of the conditions are the same, and a ternary precursor with the molecular formula Ni 0.94 Co 0.045 Mn 0.015 (OH)2 is obtained ​​​

[0134] From Figure 3 Figure 3 It can be seen that for the ternary precursor prepared in this comparative example, since strontium chloride solution was not added during the reaction process, the interior of its cross-section was relatively dense and the porosity was low, which was not conducive to the diffusion of lithium ions during the sintering process.

[0135] Comparative Example 2

[0136] Comparative Example 2 is different from Example 1 only in that strontium chloride solution was added into the reaction kettle in a continuous feeding manner, and the other conditions were the same, obtaining a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.99 (OH)2·(SrSO4) 0.005 ·(Sr(OH)2) 0.005 .

[0137] From Figure 4 Figure 4 It can be seen that for the ternary precursor prepared in Comparative Example 4, since strontium chloride solution was added into the reaction kettle in a continuous feeding manner during the reaction process, the sphericity of its secondary spherical particles was poor and there were cracked spheres. Moreover, since strontium chloride solution was continuously introduced into the reaction system, conical spikes would be formed on the surface of the secondary particles, resulting in excessive local stress and cracked spheres, thus affecting the capacity and cycle performance of the cathode material.

[0138] Comparative Example 3

[0139] Comparative Example 3 is different from Example 1 only in that the intermittent feeding method of strontium chloride solution includes: continuously adding strontium chloride solution to react for 5 h first, then stopping adding strontium chloride solution and reacting for 10 h, and repeating this as a cycle; the other conditions were the same, obtaining a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.999 (OH)2·(SrSO4) 0.0004 ·(Sr(OH)2) 0.0006 .

[0140] Comparative Example 4

[0141] Comparative Example 4 is different from Example 1 only in that the intermittent feeding method of strontium chloride solution includes: continuously adding strontium chloride solution to react for 1 h first, then stopping adding strontium chloride solution and reacting for 21 h, and repeating this as a cycle; the other conditions were the same, obtaining a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.99962 (OH)2·(SrSO4) 0.00014 ​·(Sr(OH)2) 0.00024 ternary precursor

[0142] Comparative Example 5

[0143] Comparative Example 5 is different from Example 1 only in that ferrous sulfate is used to replace the strontium chloride solution, and the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.98 Fe 0.02 (OH)2 is obtained

[0144] Comparative Example 6

[0145] Comparative Example 6 is different from Example 1 only in that there is no step of repeatedly adjusting the pH, that is, the pH value in the whole reaction system is always controlled at about 10.70, and the other conditions are the same, and a ternary precursor with the molecular formula [Ni 0.94 Co 0.045 Mn 0.015 0.99975 (OH)2·(SrSO4) 0.00025 is obtained

[0146] The ternary precursors prepared in Examples 1 to 12 and Comparative Examples 1 to 6 were subjected to characterization tests, and the results are shown in Tables 1 to 2. Among them, in Table 1, n represents the number ratio of primary particle A and primary particle B, S represents the standard deviation of the content of primary particle B in any two regions with the same area in the ternary precursor, and M1 - M2 represents the difference relationship between the content M1 of Sr in primary particle A and the content M2 of Sr in primary particle B. The specific method is as follows:

[0147] Measurement of the length and thickness of primary particle A and primary particle B and the measurement of the number ratio n of primary particle A and primary particle B: According to the scanning electron microscope image, the above indexes are measured using the measurement software Nano Measurer 1.2

[0148] Measurement of the content M1 of Sr in primary particle A and the content M2 of Sr in primary particle B and the measurement of sulfur content: Test by inductively coupled plasma atomic emission spectrometer (ICP). Measurement of secondary particle D 50 is carried out by Malvern 3000 particle size analyzer

[0149] Measurement of porosity: Take a cross-sectional view of the prepared precursor sample by scanning electron microscope and process it with Metis software

[0150] Measurement of specific surface area: Test by Micromeritics specific surface area analyzer

[0151] ​​Determination of tap density: Tested by a tap density tester.

[0152] Method for determining the standard deviation S of the content of primary particles B in any two regions with the same area of the ternary precursor: Test the content of primary particles B in any four regions of the ternary precursor by an inductively coupled plasma atomic emission spectrometer (ICP). The areas of the four regions are the same, calculate the standard deviation of primary particles B in any two regions, and take the average value.

[0153] Table 1

[0154]

[0155]

[0156] Table 2

[0157]

[0158]

[0159] From the data in Table 1 to Table 2, compared with Example 1 and Examples 4 - 5, it can be seen that controlling the intermittent feeding mode of strontium chloride solution with 0.5 h ≤ T1 ≤ 2 h and 5 h ≤ T2 ≤ 10 h is beneficial to improving the morphology, porosity, specific surface area and tap density of the ternary precursor. Compared with Example 1 and Examples 6 - 7, during the reaction process, controlling the ratio of the reaction maintenance time at high pH and the reaction maintenance time at low pH within a suitable range is beneficial to synergistically adding strontium chloride solution intermittently and better regulating the morphology, porosity, specific surface area and tap density of the ternary precursor; compared with Example 1 and Examples 8 - 9, using a strontium chloride solution with a suitable concentration is beneficial to optimizing the porosity and increasing the specific surface area and tap density of the ternary precursor; compared with Example 1 and Examples 10 - 12, during the washing process, using a combination of sodium citrate and alkali solution with a specific molar ratio can better remove sulfur impurities and strontium content in the ternary precursor, resulting in a low sulfur content in the ternary precursor and an extremely low doping amount of strontium element, even zero; compared with Example 1 and Comparative Examples 1 - 6, only by repeatedly adjusting the pH value during the reaction process, simultaneously using an intermittent feeding mode for feeding the strontium salt solution, and controlling the ratio of the non-feeding reaction time to the feeding reaction time T2 / T1 of the strontium salt solution in each cycle, can the ternary precursor prepared have a large specific surface area, good morphological uniformity, high tap density and low sulfur content under the synergistic effect.

[0160] Meanwhile, the cathode materials prepared from the ternary precursors obtained in Examples 1 to 12 and Comparative Examples 1 to 6 were assembled into coin-type lithium-ion batteries, and then their electrical properties were tested. The test results are shown in Table 3.

[0161] Among them, the method for assembling the coin-type lithium-ion battery is as follows: The cathode material, conductive agent SuperP, and binder PVDF are used to prepare the cathode material slurry according to a mass ratio of 90:5:5 using a degassing machine. After adjusting the solid content of the slurry to 39% with N-methylpyrrolidone (NMP), the adjusted slurry is coated on aluminum foil using an automatic coater, dried in a vacuum drying oven at 120 °C, rolled by a rolling press, punched by a slicing machine, and then assembled into a coin-type 2032 battery in a glove box. The electrolyte is 1.2 mol / L NaPF6, where the solvent is EC:PC:EMC = 1:1:1 (volume ratio), and an additional 2 wt% FEC is added. The separator is a glass fiber separator, and a sodium metal sheet is used as the counter electrode.

[0162] Subsequently, each coin-type half-cell was subjected to charge-discharge tests on a Blue-Energy tester in the voltage range between 1.5 V and 4.2 V. Each charge-discharge was performed 3 times at 0.1 C and 1 C, and the initial charge-discharge specific capacity and the capacity retention rate after 30 cycles at 1 C were tested. The test results are shown in Table 3 below.

[0163] Table 3

[0164]

[0165]

[0166] As can be seen from the data in Table 3, in the preparation method of the present invention, by adopting the method of repeatedly adjusting the pH value during the reaction process, and at the same time adopting an intermittent feeding method for feeding the strontium salt solution, and controlling the ratio of the non-feeding reaction time to the feeding reaction time T2 / T1 of the strontium salt solution in each cycle, under this synergistic effect, the specific surface area of the prepared ternary precursor can be made larger, the morphology uniformity is good, the tap density is high, and the sulfur content is low, thereby improving the discharge specific capacity and cycle performance of the cathode material of the lithium-ion battery.

[0167] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0168] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A ternary precursor, characterized in that, The chemical general formula of the ternary precursor is [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4) d ·(Sr(OH)2) e , where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0002, 0 ≤ e ≤ 0.0002;​ The ternary precursor is a spherical secondary particle formed by the accumulation of primary particles. Among them, the primary particles include primary particle A and primary particle B. The thickness of the primary particle A is 50nm - 150nm, and the length is 300nm - 400nm. The thickness of the primary particle B is 20nm - 40nm, and the length is 150nm - 250nm. The quantity ratio of the primary particle A to the primary particle B is 0.2 - 5. And in any two regions with the same area of the ternary precursor, the standard deviation of the content of the primary particle B is less than 1; the porosity of the ternary precursor is 10% - 20%, and the sulfur content is ≤600ppm.

2. The ternary precursor according to claim 1, wherein The ternary precursor also satisfies at least one of the following conditions: (1) The aspect ratio of the primary particle A is 2 - 8; (2) The aspect ratio of the primary particle B is 3 - 12; (3) The specific surface area of the ternary precursor is 10 m 2 / g - 30 m 2 / g; (4) The D of the ternary precursor 50 is 8 μm - 12 μm; (5) The K of the ternary precursor 90 is 1 - 2, where K 90 =(D 90 - D 10 ) / D 50 ; (6) The tap density of the ternary precursor is 2.0 g / cm 3 - 2.5 g / cm 3 .

3. The ternary precursor according to claim 1, wherein When d and e are not both zero, the Sr content in the primary particle A is M1, and the Sr content in the primary particle B is M2, M1 - M2 ≥ 0; or, d and e are both zero.

4. A method for preparing a ternary precursor as described in claims 1 to 3, characterized in that, It includes the following steps: Based on [Ni a Co b Mn c 1-d-e (OH)2·(SrSO4) d ·(Sr(OH)2) e where 0.8 ≤ a < 1.0, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 ≤ d ≤ 0.0002, 0 ≤ e ≤ 0.0002, mix nickel salt, cobalt salt, manganese salt and water to prepare a mixed salt solution;​ Under a protective atmosphere, the mixed salt solution, complexing agent solution, precipitating agent solution, and strontium salt solution are added to the reaction bottom liquid for reaction to obtain a ternary precursor slurry. Among them, the strontium salt solution is added to the reaction bottom liquid in an intermittent feeding manner, and the intermittent feeding manner includes: continuously adding the strontium salt solution for reaction for T1 hours first, and then stopping adding the strontium salt solution and reacting for T2 hours, and this is used as a cycle for repeated operation until the D of the ternary precursor slurry 50 reaches the target D 50 up to, 2.5 ≤ T2 / T1 ≤ 20; and the D of the ternary precursor slurry is regularly monitored during the reaction 50 , when the D of the ternary precursor slurry 50 is greater than the target D 50 , raise the pH to 10.80 - 11.50, and when the D of the ternary precursor slurry 50 is less than the target D 50 , lower the pH to 10.50 - 10.80, and repeat the operation like this until the D of the ternary precursor slurry 50 reaches the target D 50 up to; Age, wash, and dry the ternary precursor slurry to obtain the ternary precursor.

5. The preparation method of the ternary precursor according to claim 4, wherein 0.5 hours ≤ T1 ≤ 2 hours, 5 hours ≤ T2 ≤ 10 hours.

6. The preparation method of the ternary precursor according to claim 4, wherein The reaction time after each pH increase to 10.80 - 11.50 is T3, and the reaction time after each pH decrease to 10.50 - 10.80 is T4, 0.2 ≤ T3 / T4 ≤ 5.

7. The preparation method of the ternary precursor according to claim 4, characterized in that, In the step of mixing nickel salt, cobalt salt, manganese salt, and water to prepare a mixed salt solution, it satisfies at least one of the following conditions: (1) The total concentration of metal ions in the mixed salt solution is 1.0mol / L - 2.5mol / L; (2) The nickel salt is selected from at least one of nickel sulfate, nickel chloride, and nickel nitrate; (3) The cobalt salt is selected from at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate; (4) The manganese salt is selected from at least one of manganese sulfate, manganese chloride, and manganese nitrate.

8. The preparation method of the ternary precursor according to claim 4, wherein, In the step of adding the mixed salt solution, complexing agent solution, precipitating agent solution, and strontium salt solution to the reaction bottom liquid for reaction under a protective atmosphere, it satisfies at least one of the following conditions: (1) The protective atmosphere is selected from an inert atmosphere and / or a nitrogen atmosphere; (2) The flow rate of the mixed salt solution is 4L / h - 8L / h; (3) The concentration of the complexing agent solution is 1mol / L - 15mol / L, and the complexing agent solution is selected from at least one of ammonia water solution and sodium citrate; (4) The concentration of the precipitating agent solution is 10mol / L - 15mol / L, and the precipitating agent solution is selected from at least one of sodium hydroxide solution and sodium carbonate; (5) The flow rate of the strontium salt solution during feeding is 0.01L / h - 3L / h; (6) The concentration of the strontium salt solution is 0.01mol / L - 3.0mol / L; (7) The strontium salt solution is selected from at least one of strontium chloride solution, strontium nitrate, and strontium acetate; (8) The target D 50 is 8μm - 12μm; (9) The temperature of the reaction bottom liquid is 40°C - 70°C, the ammonia value is 1g / L - 10g / L, and the pH is 11.0 - 12.

0.

9. The preparation method of the ternary precursor according to claim 4, wherein In the washing step, the washing liquid includes an inorganic base and sodium citrate, wherein the molar ratio of the inorganic base to the sodium citrate is 1:1 - 15:

1.

10. A positive electrode material prepared by using the ternary precursor as described in claims 1 to 3.

11. A positive electrode sheet prepared by using the positive electrode material as described in claim 10.

12. A lithium-ion battery prepared by using the positive electrode sheet as described in claim 11.

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