Core-shell structure basic carbonate precursor as well as preparation method and application thereof

Abstract

The invention provides a core-shell structure basic carbonate precursor as well as a preparation method and application thereof. The core-shell structure basic carbonate precursor comprises an inner core and an outer shell, the inner core is formed by relatively loosely stacking flaky primary particles, and the main component is hydroxide, so that the volumetric specific energy of the carbonate material can be improved to a certain extent, and meanwhile, the rate capability of the material is considered; the shell is formed by relatively densely stacking dotted primary particles, the main component is carbonate, CO2 can be generated in the sintering process of the carbonate, so that the material is loose and porous, permeation of an electrolyte is facilitated, and material capacity exertion and rate capability improvement can be obviously promoted. The overall structure in the particle is loose and porous, so that the volume change of the material in the charge-discharge process can be effectively buffered, and the cycle performance of the material is improved. Therefore, the precursor can be used for preparing the positive electrode material with high rate performance, high cycle stability and volume specific capacity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and relates to core-shell structured basic carbonate precursors, their preparation methods, and applications. Background Technology

[0002] As one of the core materials of a battery, the cathode material restricts the overall performance of the battery. Cathode materials can inherit the morphology and structural characteristics of the precursor; therefore, the structure and preparation process of the precursor have a crucial impact on the performance of the cathode material.

[0003] Generally, the sintering process of carbonate precursors and lithium salts generates CO2, making the material porous and loose, which is conducive to the penetration of electrolyte and results in better capacity utilization and rate performance. However, carbonate precursors are relatively loose and have a relatively low tap density, so the prepared cathode materials often have a low volumetric energy density. In addition, the particle size grows rapidly during the synthesis of carbonate precursors, making it difficult to control the particle size of carbonate precursors within a suitable range. Hydroxide precursors are generally denser, and the volumetric energy density of the cathode material can reach a higher level. Moreover, the particle size growth rate is slower during the synthesis stage, and the precursor particle size is easier to control.

[0004] Patent application CN108862406A discloses a carbonate precursor, its preparation method, and its application. The molecular formula of this basic carbonate precursor is (Ni... x Co y M z (CO3) 1-k (OH) 2k M is one of Mn, Al, Ti, Cr, V, Sn, Zr, Fe, B, and rare earth elements. The preparation method includes three steps: 1) mixing nickel-cobalt-manganese salt or nickel-cobalt-aluminum with a growth promoter to obtain solution a; 2) mixing solution a with a precipitant to generate a solid precipitate; 3) washing, filtering, and drying the solid precipitate after the reaction to obtain the precursor. This method is characterized by its simplicity, short process, low cost, and environmental friendliness. The precursor particles obtained using this process are large (20~50 μm) with a narrow particle size distribution range (0.5~0.8 μm), and can be applied to the preparation of positive electrode materials for lithium-ion batteries. The positive electrode material can meet the requirements of high compaction, high voltage, and high cycle performance. However, the precursor material prepared by this method has a large particle size and an excessively long lithium-ion diffusion path, resulting in high material impedance and hindering electrolyte penetration, leading to low discharge capacity and rate performance. Furthermore, the method introduces organic growth promoters, which not only increases the production cost of the precursor but also makes the wastewater generated during the precursor production process difficult to treat, increasing wastewater treatment costs and posing significant environmental risks. In addition, the introduction of ammonia water during the preparation process increases production costs and is not conducive to improving the working environment and protecting the process during synthesis.

[0005] Patent application CN115872459A discloses a double-layer coated ternary precursor, its preparation method, and its application. The double-layer coated ternary precursor includes a core, an inner coating layer covering the outer surface of the core, and an outer coating layer covering the outer surface of the inner coating layer. The core comprises a ternary hydroxide, the inner coating layer comprises a ternary carbonate, and the outer coating layer comprises at least one of aluminum hydroxide, magnesium hydroxide, and titanium hydroxide. Through the synergistic effect of this special structure and material properties, the specific capacity, ion insertion / extraction efficiency, and cycle stability of the ternary cathode material can be improved. However, in the precursor disclosed in this patent application, the mass ratio of the core, inner coating layer, and outer coating layer is 1:(0.1~0.5):(0.05~0.2), with a high mass proportion of hydroxide in the core. Although this can provide a high volumetric energy density, the rate capability and power performance of this type of material are poor. Furthermore, the preparation method involves many steps, low production efficiency, and complex control, which is not conducive to industrial production. Two different types of precipitants are used successively, and parameter adjustments are involved in multiple stages during the reaction. The synthesis process includes two base liquid preparations, two aging processes, and two washing processes, which significantly increases the difficulty of process control and reduces production efficiency. Moreover, ammonium ions are introduced in both the core and inner coating layer preparation stages, which not only increases production costs but is also detrimental to environmental protection. Summary of the Invention

[0006] To address the aforementioned technical issues, this application provides a core-shell structured basic carbonate precursor, its preparation method, and its applications.

[0007] To achieve the above objectives, this application proposes the following technical solution: Firstly, a core-shell structured basic carbonate precursor is provided, wherein the chemical formula of the core-shell structured basic carbonate precursor is (Ni x Co y Mn z M a (CO3) 1-t (OH) 2t M is one or more of Al, Ti, Mg, Zr, Cr, V, Sn, Fe, B and rare earth elements, where x+y+z+a=1, and the minimum values ​​of x, y, z and a can all be 0, and 0≤t<1; the precursor includes a core and a shell, the core is composed of fine plate-like primary particles, and the shell is composed of dense dot-like primary particles.

[0008] Furthermore, the precursor has a particle size D50 of 5~20μm and a Span ≤0.9.

[0009] Furthermore, the kernel diameter is 20-65% of the particle diameter.

[0010] Furthermore, the main component of the core is hydroxide, and the main component of the shell is carbonate.

[0011] Secondly, a method for preparing a core-shell structured basic carbonate precursor is provided, including: Using a carbonate solution as the bottom liquid of the reactor, solutions of metal salts of nickel, cobalt, manganese, and M, along with a precipitant solution, are simultaneously introduced into the bottom liquid of the reactor for co-precipitation reaction to obtain a precursor slurry. The precursor slurry is then separated into solid and liquid phases, washed to obtain a solid, and dried to obtain a core-shell structured basic carbonate precursor. M is one or more of Al, Ti, Mg, Zr, Cr, V, Sn, Fe, B, and rare earth elements; the precipitant solution is a carbonate solution. The pH value of the bottom liquid in the reaction vessel meets the following requirement: pH > 10.0 based on a test temperature of 50°C; The coprecipitation reaction is divided into a nucleation stage and a particle growth stage; the pH value of the reaction system in the nucleation stage is 10.0~11.5; the pH value of the reaction system in the particle growth stage is 7.5~9.4.

[0012] Furthermore, the temperature of the coprecipitation reaction is 40~80℃.

[0013] Furthermore, the stirring speed for the coprecipitation reaction is 3.14~7.33 m / s.

[0014] Furthermore, in the bottom liquid of the reaction vessel, the carbonate is one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate, or a mixture thereof.

[0015] Furthermore, the total concentration of anions in the bottom liquid of the reaction vessel is ≥0.01mol / L.

[0016] Furthermore, the bottom liquid of the reaction vessel is 30-80% of the volume of the reaction vessel.

[0017] Furthermore, the temperature of the liquid at the bottom of the reaction vessel is 40~80℃.

[0018] Furthermore, in the precipitant solution, the carbonate is one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate, or a mixture thereof.

[0019] Furthermore, the total concentration of anions in the precipitant solution is 0.1~6 mol / L.

[0020] Furthermore, the soluble metal salts of nickel, cobalt, and manganese are one or more of sulfates and chlorides.

[0021] Furthermore, the total metal ion concentration of the metal salt solution is 0.1~2.5 mol / L.

[0022] Furthermore, the flow rate of the metal salt solution is 3*10. -4 V~7*10 -4 VL / min, where V is the volume of the reactor.

[0023] Furthermore, during the coprecipitation reaction, the clarified liquid is discharged through a concentration device.

[0024] Furthermore, the washing process uses at least one of pure water, ammonia solution, ammonium carbonate solution, and ammonium bicarbonate solution as the washing water.

[0025] Thirdly, a positive electrode material is provided, which is obtained by calcining a core-shell structured basic carbonate precursor prepared by the method described in the first aspect or the method described in the second aspect with lithium mixed with it.

[0026] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: A precursor is provided, comprising a core-shell structure, consisting of a core and an outer shell. The core is composed of loosely packed, plate-like primary particles, primarily composed of hydroxides, which can improve the volumetric energy density of carbonate materials to a certain extent while maintaining the material's rate performance. The outer shell is composed of densely packed, dot-like primary particles, also primarily composed of carbonates. The CO2 generated during carbonate sintering makes the material porous, facilitating electrolyte penetration and significantly promoting capacity utilization and rate performance. Due to the overall porous structure within the particles, volume changes during charge and discharge are effectively buffered, improving the material's cycle performance. Therefore, this precursor can be used to prepare cathode materials with high rate performance, high cycle stability, and good volumetric energy density.

[0027] The provided precursor material has a moderate particle size, with a D50 of 5–20 μm and a concentrated particle size distribution. This moderate particle size results in a shorter lithium-ion diffusion path and lower impedance in the prepared cathode material, and also facilitates electrolyte penetration, thus improving the material's discharge capacity and rate performance. Furthermore, the concentrated particle size distribution ensures relatively uniform voltage distribution across individual particles, which is beneficial for improving the material's cycle performance.

[0028] The provided preparation method is simple, highly efficient, and suitable for large-scale production. It utilizes only a carbonate precipitant, controlling the initial pH of the reaction vessel bottom solution by adjusting the carbonate concentration, and regulating the pH value by controlling the amount of carbonate precipitant during the reaction process, thus achieving a core-shell structure of "hydroxide core + carbonate shell." The synthesis process employs a one-step batch method, eliminating the need for separate preparation, filtration, washing, and subsequent seeding of the hydroxide core for secondary synthesis and growth. The steps are simple, and the production efficiency is high.

[0029] This preparation method is low-cost and more environmentally friendly; the precipitant used is carbonate, which is cheaper than hydroxide precipitants; no complexing agents or other additives are used in the synthesis system, which not only saves costs but is also more environmentally friendly. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 SEM image of the precursor prepared in Example 1.

[0032] Figure 2 EDS diagram of the precursor prepared in Example 1.

[0033] Figure 3 SEM image of the precursor prepared in Example 2.

[0034] Figure 4 SEM image of the precursor prepared for Comparative Example 1.

[0035] Figure 5 SEM image of the precursor prepared for Comparative Example 2. Detailed Implementation

[0036] Some embodiments of the present invention provide a core-shell structured basic carbonate precursor, wherein the chemical formula of the core-shell structured basic carbonate precursor is (Ni x Co y Mn z M a (CO3) 1-t (OH) 2t M is one or more of Al, Ti, Mg, Zr, Cr, V, Sn, Fe, B and rare earth elements, where x+y+z+a=1, 0≤x,y,z,a<1,0<t<1; the precursor includes a core and a shell, the core is composed of fine plate-like primary particles, and the shell is composed of dense dot-like primary particles.

[0037] In some preferred embodiments, the particle size D50 of the precursor is 5~20μm, such as 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, etc.

[0038] In some preferred embodiments, the particle size distribution width (Span) is ≤0.9, more preferably Span≤0.85, and even more preferably Span≤0.8, Span≤0.75, Span≤0.7, Span≤0.65, Span≤0.6, Span≤0.55, Span≤0.5, etc.

[0039] In some preferred embodiments, the core diameter is 20-65% of the particle diameter, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.

[0040] In some preferred embodiments, the core is mainly composed of hydroxides (more than 50%, more preferably more than 60%, further preferably more than 70%, even more preferably more than 80% or more than 90%), and may also contain a small amount of carbonates. The shell is mainly composed of carbonates (more than 50%, more preferably more than 60%, further preferably more than 70%, even more preferably more than 80% or more than 90%), and may also contain a small amount of hydroxides. In some provided embodiments, the hydroxide content decreases while the carbonate content increases from the core to the shell of the precursor. It is worth noting that the hydroxides and carbonates here specifically refer to hydroxides and carbonates of Ni, Co, Mn, and M.

[0041] Some embodiments of the present invention provide a method for preparing a core-shell structured basic carbonate precursor, comprising: Using a carbonate solution as the bottom liquid of the reactor, soluble metal salt solutions of nickel, cobalt, manganese, and M, along with a precipitant solution, are simultaneously introduced into the bottom liquid of the reactor for co-precipitation reaction to obtain a precursor slurry. The precursor slurry is then separated into solid and liquid phases, washed to obtain a solid, and dried to obtain a core-shell structured basic carbonate precursor. M is one or more of Al, Ti, Mg, Zr, Cr, V, Sn, Fe, B, and rare earth elements; the precipitant solution is a carbonate solution. The pH value of the bottom liquid of the reaction vessel meets the following requirement: pH > 10.0 with 50℃ as the test reference. Specifically, this pH value can be tested offline, for example, by taking out the slurry, placing it in a constant temperature water bath at 50℃, waiting for the temperature to stabilize, and then testing it with a pH electrode.

[0042] The coprecipitation reaction is divided into a nucleation stage and a particle growth stage; the pH value of the reaction system in the nucleation stage is 10.0~11.5; the pH value of the reaction system in the particle growth stage is 7.5~9.4.

[0043] The applicant discovered that by using a carbonate solution as the bottom solution of the reaction vessel, and by feeding a metal salt solution and a carbonate precipitate solution in a parallel stream, and by controlling the pH value of the bottom solution and the pH value of the reaction in stages (nucleation stage and growth stage), a hydroxide core composed of fine, plate-like primary particles and a carbonate shell composed of dense, dot-like primary particles can be obtained. During the nucleation and growth stages, the pH value of the reaction system can be controlled conventionally by controlling the carbonate precipitate solution. This synthesis process employs a single-step batch method, eliminating the need for separate preparation, filtration, washing, and subsequent secondary synthesis and growth of the hydroxide core. The process is simple, highly efficient, short, low-cost, and more environmentally friendly.

[0044] The pH value of the reaction system in the nucleation stage is 10~11.5, for example, 10, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4, 11.5, etc.

[0045] The pH value of the reaction system in the particle growth stage is 7.5~9.4, for example, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.4, etc.

[0046] In some embodiments, the temperature of the coprecipitation reaction is 40~80℃, for example 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc.

[0047] In some embodiments, the carbonate in the bottom liquid of the reaction vessel is one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate.

[0048] It is worth noting that the duration of the nucleation stage and the particle growth stage is conventionally controlled based on the diameter ratio of the precursor core to the shell. That is, the size of the core is determined according to the designed precursor particle size and the diameter ratio of the core to the shell. After the core grows to the designed size, the shell is then grown to the required particle size.

[0049] In some preferred embodiments, the total concentration of anions in the bottom liquid of the reaction vessel is ≥0.01mol / L.

[0050] In some preferred embodiments, the bottom liquid of the reactor is 30-80% of the reactor volume, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0051] In some preferred embodiments, the temperature of the bottom liquid in the reaction vessel is 40~80℃, for example, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc.

[0052] In some embodiments, the carbonate in the precipitant solution is one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate, or a mixture thereof.

[0053] In some embodiments, the total concentration of anions in the precipitant solution is 0.1~6 mol / L, for example 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, etc.

[0054] In some embodiments, the soluble metal salts of nickel, cobalt, and manganese are one or more of sulfates and chlorides.

[0055] In some embodiments, the total metal ion concentration of the metal salt solution is 0.1~2.5 mol / L, for example 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, etc.

[0056] In a preferred embodiment, the flow rate of the metal salt solution is 3*10⁻⁶. -4 V~7*10 -4 VL / min, for example 3*10 -4 VL / min, 3.5*10 -4 VL / min, 4*10 -4 VL / min, 4.5*10 -4 VL / min, 5*10 -4 VL / min, 5.5*10 -4 VL / min, 6*10 -4 VL / min, 6.5*10 -4 VL / min, 7*10 -4 VL / min, where V is the volume of the reactor.

[0057] In some preferred embodiments, during the co-precipitation reaction, the clarified liquid is discharged through a concentration device. Specifically, the slurry discharged through the overflow port is concentrated and then returned to the reactor to continue the reaction.

[0058] In some embodiments, the pH value during the nucleation stage can be controlled to remain constant or gradually decrease, and the pH value during the growth stage can also be controlled to remain constant or gradually decrease.

[0059] In some embodiments, the washing process uses at least one of pure water, ammonia solution, ammonium carbonate solution, and ammonium bicarbonate solution as the washing water. These reagents are effective in removing impurities such as Na and S without damaging the carbonate shell.

[0060] To facilitate understanding of the present invention, the invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0061] Example 1 First, nickel sulfate and manganese sulfate were mixed with pure water at a molar ratio of 35:65 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate was mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. 60 L of pure water and a certain amount of sodium carbonate were added to a 100 L reactor to maintain the pH of the base solution at 10.20 ± 0.10 (test temperature: 50 °C), forming the reaction base solution C. Solutions A and B were then introduced into the reaction base solution C. The reaction temperature was controlled at 60 °C, the metal salt flow rate was 50 mL / min, the stirring speed was 5.2 m / s, and the stirring paddle diameter was 200 mm. In the first stage, the pH was controlled at 10.20 ± 0.10, and the reaction duration was 20 h. In the second stage, the pH was controlled... The reaction temperature was 9.00±0.10, and the reaction duration was 80 hours. During the reaction, the supernatant was discharged in time through a concentration device. The obtained precipitate was filtered, washed with pure water, dried, and sieved to obtain a nickel-manganese binary basic carbonate precursor product. The product had a D50 of 8 μm, a Span of 0.72, an average core size of about 2.1 μm, an average shell thickness of about 2.5 μm, and a core content of about 29.6%.

[0062] SEM image as follows Figure 1 As shown, from Figure 1 It can be seen that the core is formed by the aggregation of fine, plate-like primary particles, while the outer shell is formed by the aggregation of dense, dot-like primary particles; the EDS diagram of the precursor cross-section is shown below. Figure 2 As shown, from Figure 2 It can be seen that the carbon element is scarce in the core, while it is abundant in the shell, indicating that the shell is mainly composed of carbonates, while the core is mainly composed of hydroxides, based on the reaction conditions. Therefore, the resulting precursor core is composed of fine, plate-like primary particles aggregated together, with hydroxides as its main component, while the shell is composed of dense, dot-like primary particles aggregated together, with carbonates as its main component.

[0063] Example 2 First, nickel sulfate, cobalt sulfate, manganese sulfate, and magnesium sulfate are mixed with pure water in a molar ratio of 25:9:65:1 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate is mixed with pure water to prepare a sodium carbonate solution B with a total metal ion concentration of 2 mol / L. 60 L of pure water and a certain amount of sodium carbonate are added to a 100 L reactor to bring the pH of the bottom solution to 11.00 ± 0.10 (test temperature 50 °C), forming the reaction bottom solution C. Solutions A and B are then introduced into the reaction bottom solution C, and the reaction temperature is controlled at 60 °C. The salt flow rate was 50 mL / min, the stirring speed was 5.2 m / s, and the impeller diameter was 200 mm. In the first stage, the pH was gradually decreased from 11.0 to 10.0, and the reaction lasted for 30 h. In the second stage, the pH was gradually decreased from 9.4 to 9.0, and the reaction lasted for 60 h. During the reaction, the supernatant was promptly discharged using a concentration device. The resulting precipitate was filtered, washed successively with ammonium bicarbonate solution and pure water, then dried and sieved to obtain the Mg-doped basic carbonate precursor product. SEM images are shown below. Figure 3 As shown, from Figure 3 It can be seen that the core is formed by the aggregation of small, plate-like primary particles, while the outer shell is formed by the aggregation of dense, dot-like primary particles. The product has a D50 of 7.5 μm, a Span of 0.75, an average core size of approximately 3.2 μm, an average outer shell thickness of approximately 1.7 μm, and a core content of approximately 48.5%.

[0064] Example 3 First, nickel sulfate, cobalt sulfate, and manganese sulfate were mixed with pure water in a molar ratio of 25:9:66 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate was mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. 30 L of pure water and a certain amount of sodium carbonate were added to a 100 L reactor to maintain the pH of the base solution at 10.60–10.70 (test temperature: 50 °C), forming the reaction base solution C. Solutions A and B were then introduced into the reaction base solution C. The reaction temperature was controlled at 60 °C, the metal salt flow rate was 40 mL / min, the stirring speed was 3.14 m / s, and the stirring paddle diameter was 200 mm. In the first stage, the pH was controlled at 10.60–10.70, and the reaction duration was 10 h. In the second stage, the pH was controlled... The reaction was carried out at 8.90~9.00°C for 90 hours. During the reaction, the supernatant was discharged in time through a concentration device. The precipitate was filtered, washed with pure water, dried and sieved to obtain the nickel-cobalt-manganese ternary basic carbonate precursor product. The product had a D50 of 10.3 μm, a Span of 0.69, an average core size of about 1.7 μm, an average shell thickness of about 3.9 μm, and a core content of about 17.9%.

[0065] Example 4 First, nickel sulfate, cobalt sulfate, and manganese sulfate were mixed with pure water in a molar ratio of 25:9:66 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate was mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. 50 L of pure water and a certain amount of sodium carbonate were added to a 100 L reactor to maintain the pH of the base solution at 10.40–10.50 (test temperature: 50 °C), forming the reaction base solution C. Solutions A and B were then introduced into the reaction base solution C. The reaction temperature was controlled at 60 °C, the metal salt flow rate was 60 mL / min, the stirring speed was 6 m / s, and the stirring paddle diameter was 200 mm. In the first stage, the pH was controlled at 10.40–10.50, and the reaction duration was 20 h. In the second stage, the pH was controlled... The reaction temperature was 8.80±0.1, and the reaction duration was 120 h. During the reaction, the supernatant was discharged in time through a concentration device. The obtained precipitate was filtered, washed with pure water, dried, and sieved to obtain the nickel-cobalt-manganese ternary basic carbonate precursor product. The product had a D50 of 13.5 μm, a Span of 0.65, an average core size of about 2.8 μm, an average shell thickness of about 5 μm, and a core content of about 21.9%.

[0066] Example 5 First, nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with pure water in a molar ratio of 25:9:66 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate is mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. 60 L of pure water and a certain amount of sodium carbonate are added to a 100 L reactor to bring the pH of the base solution to 11.3 (test temperature: 50 °C), forming the reaction base solution C. Solutions A and B are then introduced into the reaction base solution C, with the reaction temperature controlled at 60 °C, the metal salt flow rate at 60 mL / min, and the stirring speed at 7.33 m / min. The stirring paddle diameter was 200 mm. In the first stage, the pH of the reaction was gradually decreased from 11.3 to 10.2, and the reaction lasted for 12 hours. In the second stage, the pH was controlled at 9.0 ± 0.1, and the reaction lasted for 40 hours. During the reaction, the supernatant was discharged in time through a concentration device. The obtained precipitate was filtered, washed with pure water, dried, and sieved to obtain a nickel-cobalt-manganese ternary basic carbonate precursor product. The product had a D50 of 6.2 μm, a Span of 0.76, an average core size of about 1.5 μm, an average shell thickness of about 1.9 μm, and a core content of about 28.3%.

[0067] Example 6 First, nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with pure water in a molar ratio of 25:9:66 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate is mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. In a 100L reactor, 40L of pure water and a certain amount of sodium carbonate are added to bring the pH of the base solution to 10.8 (test temperature: 50℃), forming the reaction base solution C. Solutions A and B are then introduced into the reaction base solution C, with the reaction temperature controlled at 60℃, the metal salt flow rate at 50 mL / min, and the stirring speed at 5.2 m / s. The stirring paddle diameter was 200 mm. In the first stage, the pH of the reaction was gradually decreased from 10.8 to 10.2, and the reaction lasted for 28 hours. In the second stage, the pH was controlled at 9.0 ± 0.1, and the reaction lasted for 85 hours. During the reaction, the supernatant was discharged in time through a concentration device. The obtained precipitate was filtered, washed with pure water, dried, and sieved to obtain a nickel-cobalt-manganese ternary basic carbonate precursor product. The product had a D50 of 8.4 μm, a Span of 0.71, an average core size of approximately 2.6 μm, an average shell thickness of approximately 2.5 μm, and a core content of approximately 34.2%.

[0068] Comparative Example 1 First, nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with pure water in a molar ratio of 25:9:66 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate is mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. In a 100L reactor, 60L of pure water and a certain amount of sodium carbonate are added to bring the pH of the bottom solution to 9.30±0.10 (test temperature 50℃), forming the reaction bottom solution C. Solutions A and B are then introduced into the reaction bottom solution C, and the reaction temperature is controlled. The temperature was 60℃, the flow rate of the metal salt was 50 mL / min, the stirring speed was 5.2 m / s, the diameter of the stirring paddle was 200 mm, and the pH of the reaction was controlled at 9.30±0.10 throughout the reaction. The supernatant was promptly discharged during the reaction using a concentration device. The obtained precipitate was filtered, washed successively with ammonium bicarbonate solution and pure water, then dried and sieved to obtain the nickel-cobalt-manganese ternary basic carbonate precursor product. The product's D50 was controlled to 10 μm, and the Span was 0.61. SEM images are shown below. Figure 4 As shown, from Figure 4 It can be seen that the precursor has no core and is a secondary particle formed by the aggregation of dot-like primary particles.

[0069] Comparative Example 2 First, nickel sulfate, cobalt sulfate, and manganese sulfate are mixed with pure water in a molar ratio of 25:9:66 to prepare a metal salt solution A with a total metal ion concentration of 2 mol / L. Then, sodium carbonate is mixed with pure water to prepare a sodium carbonate solution B with a concentration of 2 mol / L. In a 100L reactor, 60L of pure water and a certain amount of sodium carbonate are added to bring the pH of the bottom solution to 9.30±0.10 (test temperature 50℃), forming the reaction bottom solution C. Solutions A and B are then introduced into the reaction bottom solution C, and the reaction temperature is controlled. The temperature was 60℃, the flow rate of the metal salt was 50 mL / min, the stirring speed was 5.2 m / s, the diameter of the stirring paddle was 200 mm, and the pH of the reaction was controlled at 9.00±0.10 throughout the reaction. The supernatant was promptly discharged during the reaction using a concentration device. The obtained precipitate was filtered, washed successively with ammonium bicarbonate solution and pure water, then dried and sieved to obtain the nickel-cobalt-manganese ternary basic carbonate precursor product. The product's D50 was controlled to 10 μm, and the Span was 0.73. SEM images are shown below. Figure 5 As shown, from Figure 5 It can be seen that the precursor has no core and is a secondary particle formed by the aggregation of dot-like primary particles.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A core-shell structured basic carbonate precursor, characterized in that, The chemical formula of the core-shell structured basic carbonate precursor is (Ni x Co y Mn z M a (CO3) 1-t (OH) 2t M is one or more of Al, Ti, Mg, Zr, Cr, V, Sn, Fe, B and rare earth elements, where x+y+z+a=1, 0<x<0.5, 0≤y<0.2, 0.5≤z<1, 0≤a<0.1, 0<t<1; the precursor includes a core and a shell, the core is composed of fine plate-like primary particles, and the shell is composed of dense dot-like primary particles.

2. The core-shell structured basic carbonate precursor as described in claim 1, characterized in that, The precursor has a particle size D50 of 5~20μm and a span ≤0.9; Preferably, the diameter of the kernel is 20-65% of the particle diameter.

3. The core-shell structured basic carbonate precursor as described in claim 1, characterized in that, The core is mainly composed of hydroxides, and the outer shell is mainly composed of carbonates.

4. A method for preparing a core-shell structured basic carbonate precursor, characterized in that, include: Under stirring conditions, using a carbonate solution as the bottom liquid of the reactor, soluble metal salt solutions of nickel, cobalt, manganese, and M, and a precipitant solution are simultaneously introduced into the bottom liquid of the reactor for co-precipitation reaction to obtain a precursor slurry. The precursor slurry is then separated into solid and liquid phases, washed to obtain a solid, and dried to obtain a core-shell structured basic carbonate precursor. M is one or more of Al, Ti, Mg, Zr, Cr, V, Sn, Fe, B, and rare earth elements; the precipitant solution is a carbonate solution. The pH value of the bottom liquid in the reaction vessel meets the following requirement: pH > 10.0 based on a test temperature of 50°C; The coprecipitation reaction is divided into a nucleation stage and a particle growth stage; the pH value of the reaction system in the nucleation stage is 10.0~11.5; the pH value of the reaction system in the particle growth stage is 7.5~9.

4.

5. The method for preparing the core-shell structured basic carbonate precursor as described in claim 4, characterized in that, The temperature of the coprecipitation reaction is 40~80℃; The stirring speed for the coprecipitation reaction is 3.14~7.33 m / s.

6. The method for preparing the core-shell structured basic carbonate precursor as described in claim 4, characterized in that, The carbonate in the bottom liquid of the reaction vessel is one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate; The total concentration of anions in the bottom liquid of the reaction vessel is ≥0.01 mol / L; The bottom liquid of the reactor is 30-80% of the reactor volume; The temperature of the bottom liquid in the reactor is 40~80℃.

7. The method for preparing the core-shell structured basic carbonate precursor as described in claim 4, characterized in that, In the precipitant solution, the carbonate is one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate; The total concentration of anions in the precipitant solution is 0.1~6 mol / L; The soluble metal salts of nickel, cobalt, and manganese are one or more of sulfates and chlorides; The total metal ion concentration of the metal salt solution is 0.1~2.5 mol / L; The flow rate of the metal salt solution is 3*10 -4 V~7*10 -4 VL / min, where V is the volume of the reactor.

8. The method for preparing the core-shell structured basic carbonate precursor as described in claim 4, characterized in that, During the coprecipitation reaction, the clear liquid is discharged through a concentration device.

9. The method for preparing the core-shell structured basic carbonate precursor as described in claim 4, characterized in that, The washing process uses at least one of the following: pure water, ammonia solution, ammonium carbonate solution, and ammonium bicarbonate solution.

10. A positive electrode material, characterized in that, The core-shell basic carbonate precursor prepared by any one of claims 1 to 3 or by any one of claims 4 to 9 is obtained by calcining lithium-containing core-shell basic carbonate precursors.

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