Alpha-type aluminum-doped cobaltous hydroxide, and preparation method and application thereof

Abstract

The disclosure provides a type alpha aluminum-doped cobalt hydroxide and a preparation method and application thereof, and relates to the technical field of positive electrode material coating materials. The method comprises the following steps: introducing an alkali liquor and a cobalt-aluminum mixed salt solution in a storage tank into a bottom liquor to perform a coprecipitation nucleus reaction under the condition that the pH value of a reaction system is controlled to be 10-12; during the coprecipitation nucleus reaction, an acidic organic additive is added to the cobalt-aluminum mixed salt solution in the storage tank which is not introduced into the bottom liquor at a fixed flow rate; when the color of the mixture of the reaction system has a change sign, the feeding of the alkali liquor is stopped, and the stirring frequency is reduced to perform a growth reaction, and the pH value of the reaction system is reduced to 9-10.5; the obtained cobalt hydroxide slurry is washed, dried and crushed, and thus the type alpha aluminum-doped cobalt hydroxide with a main phase of alpha-Co(OH)2 and a small D50 can be obtained, the type alpha aluminum-doped cobalt hydroxide has good coating effect, powder resistivity, low impedance, good doping uniformity, high first effect and excellent electrochemical performance.

Description

Technical Field

[0001] This disclosure relates to the field of cathode material coating technology, and more specifically, to an α-type aluminum-doped cobalt hydroxide, its preparation method, and its application. Background Technology

[0002] Lithium cobalt oxide cathode materials, due to their high energy density, are mainly used in the 3C (computer, communication, and consumer electronics) field. With the widespread adoption of 5G smartphones, the demand for lithium cobalt oxide is constantly increasing, which in turn drives the demand for coating materials for lithium cobalt oxide cathode materials. To improve the electrochemical performance of lithium cobalt oxide cathode materials, various active and inactive chemical substances are often coated on their surface to reduce direct contact between the cathode material surface and the electrolyte. This reduces cobalt dissolution and gas production, improving electrochemical performance such as storage gas generation. Coating a layer of nano-sized cobalt hydroxide onto lithium cobalt oxide after its first calcination in the second calcination stage, and then sintering it to form a nano-sized lithium cobalt oxide coating layer, can improve its physicochemical properties such as residual lithium, thereby improving the interfacial performance of the lithium cobalt oxide cathode material. Generally speaking, the smaller the primary cobalt hydroxide particles, the smaller the particle size, and the better the dispersibility, the better the coating effect.

[0003] With the development of 3C electronic products, people have higher and higher requirements for lithium cobalt oxide materials. Researchers have improved the voltage platform of lithium cobalt oxide cathode materials by doping them with various elements, especially aluminum, to obtain higher discharge capacity and better cycle performance. At the same time, higher requirements have been put forward for the coating material on the surface of the material. Nanoscale aluminum-doped cobalt hydroxide is used to coat and sinter lithium cobalt oxide after one firing, and finally a nanoscale aluminum-doped lithium cobalt oxide coating layer is formed on the surface of lithium cobalt oxide, which is in line with the direction of mainstream technology development.

[0004] Currently, the cobalt hydroxide prepared in the industry is mainly β-Co(OH)2, which has a brucite-like structure. β-Co(OH)2 has a small interlayer spacing (d = 0.46 nm), resulting in low activity and high impedance of the LCO obtained after sintering. Furthermore, β-Co(OH)2 requires a high pH system for precipitation, and the precipitation rates of dopants, especially aluminum and cobalt, differ significantly, making it difficult to achieve co-precipitation and uniform element distribution. The aluminum hydroxide produced by heterogeneous nucleation growth is a gel-like substance, which increases the tendency for cobalt hydroxide to agglomerate, leading to poor dispersibility and easy particle aggregation, which is detrimental to surface coating. In contrast, α-Co(OH)2 has a hydrotalcite structure with a larger interlayer spacing (d > 0.7 nm), exposing more active sites and exhibiting better sintering performance. After sintering, it yields LCO with lower impedance, promoting Li transport rates in the material and achieving better electrochemical performance. The larger interlayer spacing also facilitates Al diffusion, improving Al distribution uniformity and indirectly improving its dispersibility. However, β-Co(OH)2 is a thermally stable phase, while α-Co(OH)2 is a metastable phase. Under high temperature or high pH preparation systems, its structure is very unstable and it is easy to rapidly transform into β-Co(OH)2. Even under normal temperature or general alkaline preparation conditions, it will gradually transform into β-Co(OH)2 in the later stages of synthesis, making it difficult to form stable and high-purity α-Co(OH)2, and the preparation process is quite difficult.

[0005] CN114906878 discloses a method for preparing battery-grade cobalt hydroxide nanosheets. It uses high-concentration liquid, high stirring, and high temperature to control the nucleation burst rate to be greater than the nucleation growth rate, thereby reducing particle agglomeration and improving particle dispersion. However, the actual prepared D50 is all above 0.5 μm, and the coating effect is generally poor.

[0006] CN113816436A discloses a method for preparing amorphous highly aluminum-doped cobalt hydroxide and its application. The prepared D50 is below 0.5 μm, but the product is a β-Co(OH)2 phase. However, the performance of β-Co(OH)2 after sintering is weaker than that of α-Co(OH)2.

[0007] Therefore, how to form small-particle-size, stable and high-purity α-Co(OH)2 is a problem that needs to be solved in this field.

[0008] In view of this, this disclosure is hereby made. Summary of the Invention

[0009] The purpose of this disclosure is to provide an α-type aluminum-doped cobalt hydroxide, its preparation method, and its application.

[0010] This disclosure is implemented as follows:

[0011] In a first aspect, this disclosure provides a method for preparing α-type aluminum-doped cobalt hydroxide, comprising:

[0012] The alkaline solution and the cobalt-aluminum mixed salt solution in the storage tank are introduced into the bottom liquid. Under stirring, the pH value of the reaction system is controlled at 10-12 to carry out the co-precipitation crystal nucleation reaction. During the co-precipitation crystal nucleation reaction, an acidic organic additive is added to the cobalt-aluminum mixed salt solution in the storage tank that has not been introduced into the bottom liquid at a fixed flow rate so that the concentration of the acidic organic additive in the cobalt-aluminum mixed salt solution gradually increases.

[0013] When the color of the mixture in the reaction system shows signs of change, stop feeding the alkaline solution and continue to pass the cobalt-aluminum mixed salt solution through it. At the same time, reduce the stirring frequency and continue the growth reaction. The pH of the reaction system is reduced to 9-10.5 to obtain cobalt hydroxide slurry.

[0014] The cobalt hydroxide slurry was washed, dried and pulverized to obtain α-type aluminum-doped cobalt hydroxide.

[0015] In an optional embodiment, the acidic organic additive includes at least one of citric acid, ammonium citrate, and sodium citrate;

[0016] Preferably, the concentration of the acidic organic additive is 0.1 g / L to 3 g / L;

[0017] Preferably, the amount of acidic organic additive added is such that the pH of the cobalt-aluminum mixed salt solution is controlled to be 0.5-4.

[0018] In an optional embodiment, the flow rate of the cobalt-aluminum mixed salt solution into the bottom liquid is 25 L / h-35 L / h; the flow rate of the alkali solution into the bottom liquid is 8 L / h-12 L / h.

[0019] In an optional embodiment, the stirring frequency during the co-precipitation nucleation reaction is 45-55 Hz; and the stirring frequency during the growth reaction is 25-35 Hz.

[0020] In an optional embodiment, the reaction temperature of the co-precipitation nucleation reaction is room temperature, and the reaction time is 0.5-1 h;

[0021] Preferably, the growth reaction is carried out at room temperature for 0.2-0.5 hours.

[0022] In an optional embodiment, the cobalt-aluminum mixed salt solution is prepared by adding aluminum sulfate octadeca crystals to a cobalt salt solution and mixing.

[0023] Preferably, the cobalt salt includes at least one of cobalt chloride and cobalt sulfate;

[0024] Preferably, the cobalt concentration in the cobalt chloride is 110 g / L-130 g / L;

[0025] Preferably, the cobalt concentration in the cobalt sulfate is 100 g / L-120 g / L;

[0026] Preferably, the aluminum concentration in the cobalt-aluminum mixed salt solution is 1 g / L to 2 g / L.

[0027] In an optional embodiment, the washing includes washing at room temperature with wash water, wherein an acidic antioxidant is added to the wash water to prevent the material from oxidizing and transforming, and after washing, dehydration is performed to obtain a cobalt hydroxide filter cake with a moisture content of 40% to 60%.

[0028] Preferably, the acidic antioxidant includes at least one of ascorbic acid and citric acid.

[0029] In an optional embodiment, the drying includes drying and dehydration in an inert atmosphere or vacuum drying apparatus;

[0030] Preferably, the drying temperature is 60℃-110℃.

[0031] Secondly, this disclosure provides an α-type aluminum-doped cobalt hydroxide, which is prepared by the preparation method of α-type aluminum-doped cobalt hydroxide as described in any of the foregoing embodiments;

[0032] Preferably, the α-type aluminum-doped cobalt hydroxide has a D50 of <0.5 μm and an Al (wt%) of 0.1% to 1%.

[0033] Thirdly, this disclosure provides the application of α-type aluminum-doped cobalt hydroxide as described in the foregoing embodiments as a coating layer in the preparation of lithium-ion battery cathode materials.

[0034] This disclosure has the following beneficial effects:

[0035] The method for preparing α-type aluminum-doped cobalt hydroxide disclosed herein involves adding an acidic organic additive to a cobalt-aluminum mixed salt solution at a fixed flow rate, thereby gradually increasing the concentration of the acidic organic additive in the substrate. Simultaneously, during the co-precipitation nucleation reaction, by controlling the reaction at a high stirring frequency, a high reaction pH, a low concentration of the acidic organic additive, and a short reaction time, a large number of finely dispersed amorphous α-Co(OH)₂ nuclei can be rapidly prepared. Furthermore, due to the short synthesis time and the effect of trace amounts of acidic organic additive, although the pH is relatively high, the α-Co(OH)₂ nuclei cannot rapidly transform into β-Co(OH)₂ in a short time. This ensures that the nuclei are fine and dispersed during the co-precipitation nucleation reaction, and that the main phase is α-Co(OH)₂ nuclei. In the subsequent growth reaction stage, by stopping the feeding of the alkali solution while continuously introducing the cobalt-aluminum mixed salt solution, the pH of the reaction system gradually decreases. Since the solid content increases and the crystal nuclei have stabilized during the growth reaction, it is necessary to reduce the stirring frequency to avoid damaging the formed crystal nuclei and to make the overall growth reaction conditions more moderate. Low stirring frequency, low pH value, and high concentration of acidic organic additives synergistically reduce the risk of α-Co(OH)₂ transforming into β-Co(OH)₂, allowing the α-Co(OH)₂ structure to remain stable in the later stages of growth. Through the control of the above operations, it is possible to prepare α-type aluminum-doped cobalt hydroxide with α-Co(OH)₂ as the main phase, D50 < 0.5 μm, and Al (wt%) = 0.1%–1%. Compared with conventional β-Co(OH)₂, it has better coating effect, lower powder resistivity and impedance, better doping uniformity, higher initial efficiency, and superior electrochemical performance. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 XRD pattern of aluminum-doped cobalt hydroxide prepared by the method for preparing α-type aluminum-doped cobalt hydroxide provided in Example 1 of this disclosure;

[0038] Figure 2 SEM image of aluminum-doped cobalt hydroxide prepared by the method for preparing α-type aluminum-doped cobalt hydroxide provided in Example 1 of this disclosure;

[0039] Figure 3XRD pattern of aluminum-doped cobalt hydroxide prepared by the method for preparing α-type aluminum-doped cobalt hydroxide provided in Example 2 of this disclosure;

[0040] Figure 4 SEM image of aluminum-doped cobalt hydroxide prepared by the method for preparing α-type aluminum-doped cobalt hydroxide provided in Example 2 of this disclosure;

[0041] Figure 5 XRD pattern of aluminum-doped cobalt hydroxide prepared by the method for preparing aluminum-doped cobalt hydroxide provided in Comparative Example 1 of this disclosure;

[0042] Figure 6 SEM image of aluminum-doped cobalt hydroxide prepared by the method for preparing aluminum-doped cobalt hydroxide provided in Comparative Example 1 of this disclosure;

[0043] Figure 7 XRD pattern of aluminum-doped cobalt hydroxide prepared by the method for preparing aluminum-doped cobalt hydroxide provided in Comparative Example 2 of this disclosure;

[0044] Figure 8 SEM image of aluminum-doped cobalt hydroxide prepared by the method for preparing aluminum-doped cobalt hydroxide provided in Comparative Example 2 of this disclosure. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0046] This disclosure provides a method for preparing α-type aluminum-doped cobalt hydroxide, comprising:

[0047] The alkaline solution and the cobalt-aluminum mixed salt solution in the storage tank are introduced into the bottom liquid. Under stirring, the pH value of the reaction system is controlled at 10-12 to carry out the co-precipitation crystal nucleation reaction. During the co-precipitation crystal nucleation reaction, acidic organic additives are added to the cobalt-aluminum mixed salt solution in the storage tank that has not been introduced into the bottom liquid at a fixed flow rate so that the concentration of acidic organic additives in the cobalt-aluminum mixed salt solution gradually increases.

[0048] When the color of the mixture in the reaction system shows signs of change, stop feeding the alkali solution and continue to pass the cobalt-aluminum mixed salt solution through the flow. At the same time, reduce the stirring frequency and continue the growth reaction. The pH of the reaction system is reduced to 9-10.5 to obtain cobalt hydroxide slurry.

[0049] The cobalt hydroxide slurry was washed, dried and pulverized to obtain α-type aluminum-doped cobalt hydroxide.

[0050] Specifically, it includes the following steps:

[0051] S1, Preparation of cobalt-aluminum mixed salt solution.

[0052] A cobalt-aluminum mixed salt solution is prepared by adding aluminum sulfate octadeca crystals to a cobalt salt solution, wherein the cobalt salt includes, but is not limited to, at least one of cobalt chloride and cobalt sulfate; preferably, the cobalt concentration in the cobalt-aluminum mixed salt solution is 100g / L-130g / L and the aluminum concentration is 1g / L-2g / L.

[0053] In other embodiments of this disclosure, the cobalt concentration in the cobalt-aluminum mixed salt solution can be, for example, any one or a range between any two of 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, and 130 g / L, and the aluminum concentration can be, for example, any one or a range between any two of 1 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L, 1.5 g / L, 1.6 g / L, 1.7 g / L, 1.8 g / L, 1.9 g / L, and 2 g / L.

[0054] S2, co-precipitation nucleation reaction.

[0055] Pure water is added to the reactor, and the reactor stirring frequency is set to 45-55 Hz. Alkali solution is pumped into the pure water, and the pH is adjusted to 11-12, thus completing the preparation of the base solution. In other embodiments of this disclosure, the reactor stirring frequency can be, for example, any one or a range between 45 Hz, 48 Hz, 50 Hz, 52 Hz, 53 Hz, and 55 Hz. The pH of the base solution can, for example, be any one or a range between 11, 11.2, 11.4, 11.5, 11.7, 11.8, and 12.

[0056] A cobalt-aluminum mixed salt solution and an alkaline solution are introduced into the base solution at a flow rate of 25 L / h-35 L / h and a flow rate of 8 L / h-12 L / h, respectively. The mixture is stirred. During mixing, an acidic organic additive is continuously added to the cobalt-aluminum mixed salt solution at the same flow rate (1 L / h-10 L / h). As the cobalt-aluminum mixed salt solution and the acidic organic additive are continuously introduced into the base solution, the concentration of the acidic organic additive gradually increases as the volume of the cobalt-aluminum mixed salt solution gradually decreases. The pH of the reaction system is controlled at 10-12 for coprecipitation nucleation. The reaction temperature for coprecipitation nucleation is room temperature, and the reaction time is 0.5-1 h.

[0057] In other embodiments of this disclosure, the flow rate of the cobalt-aluminum mixed salt solution into the base solution can be, for example, any value or a range between any two of 25 L / h, 26 L / h, 27 L / h, 28 L / h, 29 L / h, 30 L / h, 31 L / h, 32 L / h, 33 L / h, 34 L / h, and 35 L / h. The flow rate of the alkali solution into the base solution can be, for example, any value or a range between any two of 8 L / h, 9 L / h, 10 L / h, 11 L / h, and 12 L / h. The flow rate of the acidic organic additive into the cobalt-aluminum mixed salt solution can be, for example, any value or a range between any two of 1 L / h, 2 L / h, 5 L / h, 8 L / h, and 10 L / h. The pH value for the coprecipitation nucleation reaction can be, for example, any one of 10, 10.2, 10.5, 10.8, 11, 11.2, 11.5, 11.8, or 12, or a range between any two. The reaction time can be, for example, any one of 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, or 1 h, or a range between any two.

[0058] In this disclosure, the acidic organic additive includes, but is not limited to, at least one of citric acid, ammonium citrate, and sodium citrate; preferably, the concentration of the acidic organic additive is 0.1 g / L to 3 g / L; preferably, the amount of acidic organic additive added is used to control the pH of the cobalt-aluminum mixed salt solution to be 0.5-4.

[0059] In other embodiments of this disclosure, the concentration of the acidic organic additive can be, for example, a range of 0.1 g / L, 0.3 g / L, 0.5 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.2 g / L, 2.5 g / L, or 3 g / L, or any combination thereof. The amount of acidic organic additive added is used to control the pH of the cobalt-aluminum mixed salt solution to be any range of 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, or 4, or any combination thereof.

[0060] The acidic organic additive in this disclosure can simultaneously complex cobalt and aluminum, reducing the precipitation rate of aluminum and ensuring uniform co-precipitation of cobalt and aluminum. Furthermore, the acidic organic additive can, to some extent, raise the energy barrier for the transformation from α-Co(OH)₂ to β-Co(OH)₂, better suppressing the rapid phase transition. The concentration of the acidic organic additive in the cobalt-aluminum solution is gradually increased because a large number of crystal nuclei need to be prepared initially, and the acidic organic additive inhibits the formation of these nuclei, so excessive addition is not advisable. As time progresses and crystal nuclei gradually form, the influence of the acidic organic additive on nuclei formation gradually decreases, but the risk of the transformation from α-Co(OH)₂ to β-Co(OH)₂ gradually increases. Therefore, it is necessary to gradually increase the concentration of the acidic organic additive. In this disclosure, by continuously adding a cobalt-aluminum mixed salt solution to the base solution and continuously introducing the acidic organic additive into the cobalt-aluminum mixed salt solution, the concentration of the acidic organic additive in the base solution can be gradually increased, thereby effectively reducing the risk of the transformation from α-Co(OH)₂ to β-Co(OH)₂ without affecting crystal nuclei formation.

[0061] Furthermore, in the coprecipitation nucleus reaction process of this disclosure, the stirring frequency is relatively fast, the reaction pH is relatively high, the concentration of acidic organic additives is relatively low, and the reaction time is short. Among these, under high stirring and relatively high pH conditions, a large number of amorphous α-Co(OH)2 nuclei with fine and dispersed primary particles can be rapidly prepared. At the same time, due to the short synthesis time and the effect of trace amounts of acidic organic additives, although the pH is relatively high, the α-Co(OH)2 nuclei cannot be rapidly transformed into β-Co(OH)2 in a short time. Therefore, the nuclei are ensured to be fine and dispersed during the coprecipitation nucleus reaction process, and the main phase is ensured to be α-Co(OH)2 nuclei.

[0062] S3, growth response.

[0063] When the color of the mixture in the reaction system shows signs of change, stop feeding the alkali solution and continue to pass the cobalt-aluminum mixed salt solution through it. At the same time, reduce the stirring frequency to 25-35 Hz and continue the growth reaction. The reaction temperature of the growth reaction is room temperature, the reaction time is 0.2-0.5 h, and the pH of the reaction system is reduced to 9-10.5. When the feed rate of the reactor is reached, stop feeding to obtain cobalt hydroxide slurry.

[0064] In this disclosure, during the growth reaction, by stopping the feeding of the alkaline solution while continuously introducing the cobalt-aluminum mixed salt solution, the pH of the reaction system gradually decreases. Simultaneously, due to the continuous addition of acidic organic additives to the cobalt-aluminum mixed salt solution, the concentration of the acidic organic additives in the cobalt-aluminum mixed salt solution increases, further decreasing the pH of the reaction system. Since the solid content increases and the crystal nuclei have been stably formed during the growth reaction stage, it is necessary to reduce the stirring frequency to avoid destroying the formed crystal nuclei, making the overall growth reaction conditions more moderate. The low stirring frequency, low pH value, and high concentration of acidic organic additives can synergistically reduce the risk of α-Co(OH)2 transforming into β-Co(OH)2, allowing the α-Co(OH)2 structure to remain stable in the later stages of growth.

[0065] In other embodiments of this disclosure, the stirring frequency during the growth reaction stage is any one or a range between 25 Hz, 28 Hz, 30 Hz, 32 Hz, and 35 Hz. The reaction time, for example, can be any one or a range between 0.2 h, 0.3 h, 0.4 h, and 0.5 h. The pH of the reaction system is any one or a range between 9, 9.2, 9.5, 9.8, 10, 10.2, and 10.5.

[0066] S4, Post-processing.

[0067] The cobalt hydroxide slurry was washed, dried and pulverized to obtain α-type aluminum-doped cobalt hydroxide.

[0068] The washing process includes washing at room temperature with wash water, adding an acidic antioxidant to the wash water to prevent the material from oxidizing and transforming, and dehydrating after washing to obtain a cobalt hydroxide filter cake with a moisture content of 40% to 60%; preferably, the acidic antioxidant includes at least one of ascorbic acid and citric acid.

[0069] Drying includes dehydration in a low-temperature inert atmosphere or a low-temperature vacuum drying device; preferably, the drying temperature is 60℃-110℃.

[0070] In this disclosure, by adding an acidic antioxidant during the washing process and drying it in a low-temperature inert atmosphere or a low-temperature vacuum drying device, the oxidation and transformation of the material can be effectively prevented, and the α-Co(OH)2 structure can remain structurally stable in the post-treatment stage.

[0071] The α-type aluminum-doped cobalt hydroxide prepared by the above method has α-Co(OH)2 as its main phase, D50 < 0.5 μm, and Al (wt%) = 0.1% to 1%.

[0072] α-Co(OH)2 has a larger interlayer spacing, which makes it easier for Al to diffuse within it, resulting in better Al uniformity after sintering. In addition, it has more active sites to promote sintering, resulting in lower impedance after sintering.

[0073] Furthermore, this disclosure also provides the application of the above-mentioned α-type aluminum-doped cobalt hydroxide as a coating layer in the preparation of lithium-ion battery cathode materials. The α-type aluminum-doped cobalt hydroxide prepared by this disclosure has a stable α-Co(OH)2 phase, which has a better coating effect than conventional β-Co(OH)2, with low powder resistivity, low impedance, good doping uniformity, high initial efficiency, and excellent electrochemical performance.

[0074] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0075] Example 1

[0076] This embodiment provides an α-type aluminum-doped cobalt hydroxide, the preparation method of which includes the following steps:

[0077] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 130 g / L and an aluminum ion concentration of 1.4 g / L using cobalt chloride and aluminum sulfate octadechydrate crystals. Prepare a citric acid monohydrate solution with a concentration of 2 g / L.

[0078] S2. Add 50L of pure water to a 100L reactor. Set the reactor stirring frequency to 50Hz, then pump 10mol / L alkali solution into the bottom solution and adjust the pH to around 11.8. The bottom solution preparation is complete. Continue to pump alkali solution and cobalt-aluminum mixed solution into the reactor simultaneously, while pumping 2g / L citric acid solution into the cobalt-aluminum mixed solution. During this process, the cobalt solution flow rate is 30L / h, the alkali solution flow rate is around 10L / h, and the citric acid solution flow rate is 3L / h. After 0.8 hours of synthesis, the pH of the cobalt-aluminum mixed solution gradually decreases from 2.9 to 1.2, and the pH in the reactor gradually decreases from 11.8 to around 10.2. The materials begin to show slight signs of change.

[0079] S3. Stop feeding the alkaline solution, reduce the stirring frequency to 30Hz, and continue the reaction for 0.3h. The pH of the cobalt-aluminum mixed solution drops from 1.2 to 0.8, and the pH of the slurry in the reactor drops from 10.2 to 9.5. When the feed rate of the reactor is reached, stop feeding, and finally obtain cobalt hydroxide slurry.

[0080] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes, with 1 g / L of ascorbic acid added to the wash water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 55% is obtained. The 55% moisture content cobalt hydroxide filter cake is dried at 60°C for 12 hours in an inert atmosphere, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product. XRD is shown below. Figure 1It mainly consists of pure α-Co(OH)2, as shown in the SEM image. Figure 2 .

[0081] Example 2

[0082] This embodiment provides an α-type aluminum-doped cobalt hydroxide, the preparation method of which is basically the same as that of Example 1, the only difference being the concentration of the added acidic organic additive, specifically including the following steps:

[0083] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 130 g / L and an aluminum ion concentration of 1.4 g / L using cobalt chloride and aluminum sulfate octadechydrate crystals. Prepare a citric acid monohydrate solution with a concentration of 1 g / L.

[0084] S2. Add 50L of pure water to the 100L reactor. Set the reactor stirring frequency to 50Hz, then pump 10mol / L alkali solution into the bottom solution and adjust the pH to around 11.8. The bottom solution preparation is complete. Continue to pump alkali solution and cobalt-aluminum mixed solution into the reactor simultaneously, while pumping 1g / L citric acid solution into the cobalt-aluminum mixed solution. During this process, the cobalt solution flow rate is 30L / h, the alkali solution flow rate is around 10L / h, and the citric acid solution flow rate is 5L / h. After 0.8 hours of synthesis, the pH of the cobalt-aluminum mixed solution gradually decreases from 2.9 to 1.3, and the pH in the reactor gradually decreases from 11.8 to around 10.3. The materials begin to show slight signs of change.

[0085] S3. Stop feeding the alkaline solution, reduce the stirring frequency to 30Hz, and continue the reaction for 0.3h. The pH of the cobalt-aluminum mixed solution drops from 1.2 to 0.9, and the pH of the slurry in the reactor drops from 10.2 to 9.6. When the feed rate of the reactor is reached, stop feeding, and finally obtain cobalt hydroxide slurry.

[0086] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes, with 1 g / L of ascorbic acid added to the wash water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 56% is obtained. The cobalt hydroxide filter cake with a moisture content of 56% is dried at 60°C for 12 hours in an inert atmosphere, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product. XRD is shown below. Figure 3 It mainly consists of pure α-Co(OH)2, as shown in the SEM image. Figure 4 .

[0087] Example 3

[0088] This embodiment provides an α-type aluminum-doped cobalt hydroxide, the preparation method of which includes the following steps:

[0089] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 100 g / L and an aluminum ion concentration of 1 g / L using cobalt sulfate and aluminum sulfate octadechydrate crystals. Prepare a citric acid monohydrate solution with a concentration of 0.5 g / L.

[0090] Add 50L of pure water to the S2 100L reactor. Set the reactor stirring frequency to 55Hz, then pump 10mol / L alkali solution into the bottom solution and adjust the pH to around 11. The bottom solution preparation is complete. Continue to pump alkali solution and cobalt-aluminum mixed solution into the reactor simultaneously, while simultaneously pumping citric acid solution into the cobalt-aluminum mixed solution. During this process, the flow rate of cobalt solution is 35L / h, the flow rate of alkali solution is around 12L / h, and the flow rate of citric acid solution is 10L / h. After 0.5 hours of synthesis, the pH of the cobalt-aluminum mixed solution gradually decreases from 2.8 to 1.3, and the pH in the reactor gradually decreases from 11 to around 10.4. The materials begin to show slight signs of transformation.

[0091] S3. Stop feeding the alkaline solution, reduce the stirring frequency to 35Hz, and continue the reaction for 0.2h. The pH of the cobalt-aluminum mixed solution drops from 1.3 to 0.9, and the pH of the slurry in the reactor drops from 10.4 to 9.6. When the feed rate of the reactor is reached, stop feeding, and finally obtain cobalt hydroxide slurry.

[0092] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes. 1 g / L of ascorbic acid needs to be added to the washing water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 55% is obtained. The cobalt hydroxide filter cake with a moisture content of 55% is dried in a vacuum drying oven at 90°C for 12 hours, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product.

[0093] Example 4

[0094] This embodiment provides an α-type aluminum-doped cobalt hydroxide, the preparation method of which includes the following steps:

[0095] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 110 g / L and an aluminum ion concentration of 2 g / L using cobalt sulfate and aluminum sulfate octadechydrate crystals. Prepare a citric acid monohydrate solution with a concentration of 2 g / L.

[0096] Add 50L of pure water to the S2 100L reactor. Set the reactor stirring frequency to 45Hz, then pump 10mol / L alkali solution into the bottom solution and adjust the pH to around 12. The bottom solution preparation is complete. Continue to pump alkali solution and cobalt-aluminum mixed solution into the reactor simultaneously, while simultaneously pumping citric acid solution into the cobalt-aluminum mixed solution. During this process, the flow rate of cobalt solution is 25L / h, the flow rate of alkali solution is about 8L / h, and the flow rate of citric acid solution is 4L / h. After 1 hour of synthesis, the pH of the cobalt-aluminum mixed solution gradually decreases from 2.8 to 1.4, and the pH in the reactor gradually decreases from 12 to around 10.6. The materials begin to show slight signs of change.

[0097] S3. Stop feeding the alkaline solution, reduce the stirring frequency to 25Hz, and continue the reaction for 0.5h. The pH of the cobalt-aluminum mixed solution drops from 1.4 to 0.9, and the pH of the slurry in the reactor drops from 10.6 to 9.7. When the feed rate of the reactor is reached, stop feeding, and finally obtain cobalt hydroxide slurry.

[0098] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes. Citric acid of 1 g / L needs to be added to the washing water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 55% is obtained. The cobalt hydroxide filter cake with a moisture content of 55% is dried at 110°C for 12 hours in an inert atmosphere, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product.

[0099] Comparative Example 1

[0100] This comparative example is basically the same as Example 1, except that no acidic organic additives were added, and the pH decrease was significant. Specifically, it includes the following steps:

[0101] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 130 g / L and an aluminum ion concentration of 1.4 g / L using cobalt chloride and aluminum sulfate octadechydrate crystals.

[0102] Add 50L of pure water to the S2 100L reactor, set the reactor stirring frequency to 50Hz, and then pump 10mol / L alkali solution into the bottom solution. Adjust the pH to around 11.8, and the bottom solution preparation is complete. Continue to pump alkali solution and cobalt-aluminum mixed solution into the reactor simultaneously, and synthesize for 0.5 hours. By controlling and adjusting the pH in the reactor, gradually decrease it from 11.8 to around 10.6, and the materials begin to show slight signs of transformation.

[0103] S3. Stop adding alkali solution, reduce the stirring frequency to 30Hz, continue the reaction for 0.2h, control the pH of the slurry in the reactor to decrease from 10.6 to 9.8, and finally obtain cobalt hydroxide slurry.

[0104] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes, with 1 g / L of ascorbic acid added to the wash water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 56% is obtained. The 56% moisture content cobalt hydroxide filter cake is dried in an inert atmosphere or vacuum drying oven for 12 hours, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product. XRD is shown below. Figure 5 It mainly consists of β-Co(OH)2+α-Co(OH)2, as shown in the SEM image. Figure 6 .

[0105] Comparative Example 2

[0106] This comparative example is essentially the same as Example 1, except that no acidic organic additives were added, and the pH decrease was smaller. Specifically, it includes the following steps:

[0107] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 130 g / L and an aluminum ion concentration of 1.4 g / L using cobalt chloride and aluminum sulfate octadechydrate crystals.

[0108] Add 50L of pure water to the S2 100L reactor, set the reactor stirring frequency to 50Hz, and then pump 10mol / L alkali solution into the bottom solution. Adjust the pH to around 11.8, and the bottom solution preparation is complete. Continue to pump alkali solution and cobalt-aluminum mixed solution into the reactor simultaneously, and synthesize for 0.3 hours. By controlling and adjusting the pH in the reactor, gradually decrease it from 11.8 to around 11.2, and the materials begin to show slight signs of transformation.

[0109] S3. Stop adding alkali solution, reduce the stirring frequency to 30 Hz, continue the reaction for 0.2 h, control the pH of the slurry in the reactor to decrease from 11.2 to 10.8, and finally obtain cobalt hydroxide slurry.

[0110] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes, with 1 g / L of ascorbic acid added to the wash water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 55% is obtained. The 55% moisture content cobalt hydroxide filter cake is dried in an inert atmosphere or vacuum drying oven for 12 hours, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product. XRD is shown below. Figure 7 It mainly consists of pure β-Co(OH)2, as shown in the SEM image. Figure 8 .

[0111] Comparative Example 3

[0112] This comparative example is basically the same as Example 1, except that in this comparative example, the acidic organic additive is not introduced into the cobalt-aluminum mixed solution, but directly into the base solution. The specific steps include the following:

[0113] S1. Prepare a cobalt-aluminum mixed solution with a cobalt concentration of 130 g / L and an aluminum ion concentration of 1.4 g / L using cobalt chloride and aluminum sulfate octadechydrate crystals. Prepare a citric acid monohydrate solution with a concentration of 3 g / L.

[0114] S2. Add 50L of pure water to a 100L reactor. Set the reactor stirring frequency to 50Hz, then pump 10mol / L alkali solution into the bottom solution. Adjust the pH to approximately 11.8, completing the bottom solution preparation. Continue to pump alkali solution, cobalt-aluminum mixed solution, and citric acid solution into the reactor simultaneously. During this process, the cobalt solution flow rate is approximately 30L / h, the alkali solution flow rate is approximately 10L / h, and the citric acid solution flow rate is approximately 3L / h. After 0.8 hours of synthesis, the pH in the reactor gradually decreases from 11.8 to approximately 10.2, and the materials begin to show slight signs of transformation.

[0115] S3. Stop adding alkaline solution, reduce the stirring frequency to 30 Hz, and continue to introduce cobalt-aluminum mixed solution and citric acid solution in parallel. React for 0.3 h. The pH of the slurry in the reactor will decrease from 10.2 to 9.5, and finally cobalt hydroxide slurry will be obtained.

[0116] S4. The synthesized cobalt hydroxide slurry is subjected to two slurry washing processes. 1 g / L of ascorbic acid needs to be added to the washing water. After washing and dehydration, a cobalt hydroxide filter cake with a moisture content of 55% is obtained. The cobalt hydroxide filter cake with a moisture content of 55% is dried in an inert atmosphere or vacuum drying oven for 12 hours, and then pulverized to obtain a well-dispersed aluminum-doped nano-sized cobalt hydroxide product.

[0117] Comparative Example 4

[0118] This comparative example is basically the same as Example 1, except that in this comparative example, steps S2 and S3 are both performed at a frequency of 50Hz.

[0119] Experimental Example 1

[0120] This experiment tested the physicochemical properties of Examples 1-4 and Comparative Examples 1-4 above. The test results are shown in Table 1.

[0121] Table 1: Physicochemical properties of cobalt hydroxide in the examples and comparative examples

[0122]

[0123]

[0124] As can be seen from the table above, the examples and comparative examples of this disclosure all yielded aluminum-doped nano-sized cobalt hydrogen. The D50 of Examples 1-4 was significantly lower than that of Comparative Examples 1-4, and the XRD phase of Examples 1-4 was mainly α-Co(OH)2, while the XRD phase of the comparative examples was mainly α-Co(OH)2+β-Co(OH)2 or pure β-Co(OH)2. Comparative Example 3 illustrates that the method of feeding acidic organic additives without prior complexation with aluminum is not conducive to improving the uniformity of Al in the hydrogen hydroxide and thus hinders performance improvement.

[0125] Experimental Example 2

[0126] Based on the above examples and comparative examples, this experimental example prepared several lithium cobalt oxide materials coated with cobalt hydroxide nanosheets, as well as a blank example of uncoated lithium cobalt oxide material. The specific process is as follows:

[0127] (1) Take 200g of cobalt hydroxide nanosheets and 20kg of LiCoO2 (LCO) material from the examples and comparative examples and mix them in a three-dimensional mixer for 30 minutes.

[0128] (2) The mixed material was placed in an air-filled chamber furnace for sintering at a temperature of 950°C for 8 hours. After sintering, the material was allowed to cool naturally and then sieved through a 325-mesh sieve to obtain LiCoO2 coated with cobalt hydroxide nanosheets for later use. The powder resistivity of the coated and uncoated samples was also tested.

[0129] (3) The above cobalt hydroxide nanosheet-coated LiCoO2 material and uncoated LiCoO2 material were used as positive electrodes and lithium sheets as negative electrodes, respectively, and coin cells were assembled. The first-cycle charge-discharge capacity was tested at a current density of 0.1C on the Blue Electric test cabinet, and the first-cycle coulombic efficiency was calculated. The capacity retention rate at a current density of 1C was also tested.

[0130] The results of this experiment are shown in Table 2 below:

[0131] Table 2: Electrochemical performance indicators of the test examples

[0132]

[0133]

[0134] Table 2 shows that the uncoated sample had a high powder resistivity. After coating with cobalt hydroxide, the powder resistivity decreased. The higher the α-phase content in the cobalt hydroxide nanosheets, the lower the powder resistivity. The cobalt hydroxide-coated sample exhibited a higher first-cycle coulombic efficiency. The higher the α-phase content in the cobalt hydroxide nanosheets, the higher the first-cycle efficiency, and the enhanced cycling performance. In Comparative Example 1, no acidic organic additive was added, and the pH decreased significantly, which led to a significant increase in resistivity and a significant decrease in first-cycle coulombic efficiency. In Comparative Example 2, no acidic organic additive was added, and the pH decreased only slightly. In this case, the resistivity increased significantly, and the first-cycle coulombic efficiency decreased significantly. This fully demonstrates that the addition of acidic organic additives in this application can reduce the transformation of α-Co(OH)2 crystal nuclei to β-Co(OH)2. Furthermore, the acidic organic additives need to work synergistically with pH changes to achieve better results. In Comparative Example 3, the acidic organic additive was not pre-complexed with aluminum and was directly fed into the product. This was detrimental to improving the uniformity of Al in the hydroxide hydrate, thus hindering performance improvement and leading to a significant increase in resistivity and a significant decrease in the coulombic efficiency in the first week. In Comparative Example 4, the stirring frequency was maintained at a high frequency. Under these conditions, the reaction was more vigorous, increasing the risk of the transformation of α-Co(OH)₂ to β-Co(OH)₂. This resulted in the presence of β-Co(OH)₂ in the final product, ultimately leading to a significant increase in resistivity and a significant decrease in the coulombic efficiency in the first week.

[0135] In summary, the method for preparing α-type aluminum-doped cobalt hydroxide provided in this disclosure involves adding an acidic organic additive to a cobalt-aluminum mixed salt solution at a fixed flow rate, thereby gradually increasing the concentration of the acidic organic additive in the base solution. Simultaneously, during the co-precipitation nucleation reaction, by controlling the reaction at a high stirring frequency, a high reaction pH, a low concentration of the acidic organic additive, and a short reaction time, a large number of finely dispersed amorphous α-Co(OH)₂ nuclei can be rapidly prepared. Furthermore, due to the short synthesis time and the effect of trace amounts of acidic organic additive, although the pH is relatively high, the α-Co(OH)₂ nuclei cannot rapidly transform into β-Co(OH)₂ in a short time. This ensures that the nuclei are fine and dispersed during the co-precipitation nucleation reaction, and that the main phase is α-Co(OH)₂ nuclei. In the subsequent growth reaction stage, by stopping the feeding of the alkali solution while continuously introducing the cobalt-aluminum mixed salt solution, the pH of the reaction system gradually decreases. Since the solid content increases and the crystal nuclei have stabilized during the growth reaction, it is necessary to reduce the stirring frequency to avoid damaging the formed crystal nuclei and to make the overall growth reaction conditions more moderate. Low stirring frequency, low pH value, and high concentration of acidic organic additives synergistically reduce the risk of α-Co(OH)₂ transforming into β-Co(OH)₂, allowing the α-Co(OH)₂ structure to remain stable in the later stages of growth. Through the control of the above operations, it is possible to prepare α-type aluminum-doped cobalt hydroxide with α-Co(OH)₂ as the main phase, D50 < 0.5 μm, and Al (wt%) = 0.1%–1%. Compared with conventional β-Co(OH)₂, it has better coating effect, lower powder resistivity and impedance, better doping uniformity, higher initial efficiency, and superior electrochemical performance.

[0136] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A method for preparing α-type aluminum-doped cobalt hydroxide, characterized in that, It includes: The alkaline solution and the cobalt-aluminum mixed salt solution in the storage tank are passed into a bottom liquid with a pH of 11-12. Under stirring, the pH of the reaction system is controlled to be 10-10.8 to carry out a co-precipitation crystal nucleation reaction. During the co-precipitation crystal nucleation reaction, an acidic organic additive is added to the cobalt-aluminum mixed salt solution in the storage tank that has not been passed into the bottom liquid at a fixed flow rate so that the concentration of the acidic organic additive in the cobalt-aluminum mixed salt solution gradually increases. When the color of the mixture in the reaction system shows signs of change, stop feeding the alkaline solution and continue to pass the cobalt-aluminum mixed salt solution through it. At the same time, reduce the stirring frequency to carry out the growth reaction. The pH of the reaction system is reduced to 9-10.5 to obtain cobalt hydroxide slurry. The cobalt hydroxide slurry was washed, dried, and pulverized to obtain α-type aluminum-doped cobalt hydroxide; The acidic organic additive is citric acid; the concentration of the acidic organic additive is 0.1 g / L to 3 g / L; the amount of acidic organic additive added is used to control the pH of the cobalt-aluminum mixed salt solution to be 0.5-4. The flow rate of the cobalt-aluminum mixed salt solution into the base liquid is 25 L / h-35 L / h; the flow rate of the alkaline solution into the base liquid is 8 L / h-12 L / h; and the flow rate of the acidic organic additive into the cobalt-aluminum mixed salt solution is 1 L / h-10 L / h. The stirring frequency during the co-precipitation nucleation reaction is 45-55 Hz; the stirring frequency during the growth reaction is 25-35 Hz. The co-precipitation nucleation reaction is carried out at room temperature for 0.5-1 h; the growth reaction is carried out at room temperature for 0.2-0.5 h.

2. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 1, characterized in that, The cobalt-aluminum mixed salt solution is prepared by adding aluminum sulfate crystals in octadecahydrate to a cobalt salt solution.

3. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 2, characterized in that, The cobalt salt includes at least one of cobalt chloride and cobalt sulfate.

4. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 2, characterized in that, The aluminum concentration in the cobalt-aluminum mixed salt solution is 1 g / L-2 g / L.

5. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 1, characterized in that, The washing process includes washing at room temperature with wash water, in which an acidic antioxidant is added to prevent the material from oxidizing and transforming. After washing, the material is dehydrated to obtain a cobalt hydroxide filter cake with a moisture content of 40% to 60%.

6. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 5, characterized in that, The acidic antioxidants include at least one of ascorbic acid and citric acid.

7. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 1, characterized in that, The drying process includes drying and dehydration in an inert atmosphere or vacuum drying equipment.

8. The method for preparing α-type aluminum-doped cobalt hydroxide according to claim 7, characterized in that, The drying temperature is 60℃-110℃.

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