High-aluminum-doped cobalt hydroxide as well as preparation method and application thereof

Abstract

The invention relates to highly aluminum-doped cobalt hydroxide and a preparation method and application thereof, the highly aluminum-doped cobalt hydroxide comprises cobalt hydroxide and an aluminum element doped in the cobalt hydroxide, the highly aluminum-doped cobalt hydroxide is spherical, and the aluminum doping amount of the highly aluminum-doped cobalt hydroxide is 9000-10000 ppm. The high-aluminum-doped cobalt hydroxide provided by the invention has the advantages of spherical morphology and high aluminum-doped content, and the spherical morphology and the aluminum-doped content cooperate with each other to jointly improve the electrochemical performance of the positive electrode material prepared from the high-aluminum-doped cobalt hydroxide during high-voltage operation of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of cobalt hydroxide, and in particular to highly aluminum-doped cobalt hydroxide and a preparation method and application thereof. Background Art

[0002] As 3C electronic products develop towards thinner, lighter, and longer-lasting batteries, lithium cobalt oxide (LiCoO2), as a mainstream cathode material, has become a research focus, with its energy density and cycling stability. LiCoO2 is typically produced by sintering cobalt trioxide (Co3O4) with a lithium source at high temperatures. The performance of Co3O4 is directly influenced by the morphology and structure of its precursor, cobalt hydroxide (Co(OH)2).

[0003] However, the precursor cobalt hydroxide (Co(OH)2) produced by current technology has the following problems: First, insufficient morphology control: cobalt hydroxide synthesized by traditional wet method is prone to irregular particles or agglomeration, resulting in uneven particle size distribution of cobalt trioxide after sintering, which in turn affects the compaction density and electrochemical properties of lithium cobalt oxide; second, poor doping uniformity: aluminum doping can improve the structural stability of the material, but existing methods (such as mechanical mixing) are prone to uneven distribution of aluminum elements and low doping content, resulting in local lattice distortion after sintering, causing battery flatulence or capacity attenuation; third, low process efficiency: existing preparation processes mostly rely on complex surfactant systems or multiple sintering, which are costly and difficult to scale.

[0004] In response to the above problems, the existing technology attempts to improve material performance by controlling the sintering kiln pressure, optimizing the coating process or improving the doping method, but it still faces challenges such as insufficient sphericity and poor doping performance. For example, the existing technology CN117712310A discloses a positive electrode material and its preparation method using dry-coating cobalt hydroxide technology, which includes the following steps: S100: preparing cobalt hydroxide particles, using traditional methods to prepare cobalt hydroxide particles to ensure that the particle morphology and size are consistent; S200: coating with a protective film, mixing the cobalt hydroxide particles with the selected protective film material, and drying; S300: characterization and testing, characterizing and testing the coated positive electrode material. However, the sphericity and performance of the particles prepared by the above-mentioned existing technology still need to be improved.

[0005] Therefore, the development of an aluminum-doped cobalt hydroxide with high particle sphericity, high aluminum doping content and uniform doping and its preparation method are of great significance to promoting the commercial application of high-voltage lithium cobalt oxide positive electrode materials. Summary of the Invention

[0006] To address the above technical problems, the present invention aims to provide a highly aluminum-doped cobalt hydroxide, its preparation method, and its application. The highly aluminum-doped cobalt hydroxide provided by the present invention has the advantages of a spherical morphology and a high aluminum content. These two advantages synergistically improve the electrochemical cycling performance of the cathode material prepared using the highly aluminum-doped cobalt hydroxide as a raw material when the battery is operated at high voltage.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a highly aluminum-doped cobalt hydroxide, comprising cobalt hydroxide and an aluminum element doped in the cobalt hydroxide. The highly aluminum-doped cobalt hydroxide has a spherical morphology and an aluminum doping amount of 9000-10000 ppm.

[0009] In the present invention, the "aluminum content of highly aluminum-doped cobalt hydroxide" refers to the percentage of the mass of aluminum element to the total mass of highly aluminum-doped cobalt hydroxide.

[0010] The morphology of the highly aluminum-doped cobalt hydroxide provided by the present invention is a spherical structure, which can effectively improve the stacking performance and structural stability of cobalt hydroxide, maintain the morphological integrity of the subsequently prepared cobalt trioxide, avoid particle breakage and agglomeration, easily form a more compact electrode structure, and can reduce the occurrence of side reactions between the electrode material and the electrolyte, thereby improving the energy density and cycle stability of the cobalt carbonate positive electrode material. On the other hand, the highly aluminum-doped cobalt hydroxide provided by the present invention has a high aluminum content, which can promote the formation of a more stable lattice structure, slow down the volume change and phase change of the positive electrode material prepared by the subsequent process during the battery charge and discharge process, improve the cycle life of the positive electrode material, and optimize the electron / ion transmission path of the positive electrode material, thereby improving the cycle performance of the battery under high voltage. The synergistic effect of the spherical morphology and high aluminum content of the highly aluminum-doped cobalt hydroxide provided by the present invention jointly improves the electrochemical cycle performance of the positive electrode material prepared with highly aluminum-doped cobalt hydroxide as raw material when the battery is running at high voltage.

[0011] Preferably, the specific surface area of ​​the highly aluminum-doped cobalt hydroxide is 2-5 m 2 / g, for example 2.0m 2 / g, 2.2m 2 / g, 2.4m 2 / g, 2.6m 2 / g, 2.8m 2 / g, 3.0m 2 / g, 3.2m 2 / g, 3.4m 2 / g, 3.6m 2 / g, 3.8m 2 / g, 4.0m 2 / g, 4.2m2 / g, 4.4m 2 / g, 4.6m 2 / g, 4.8m 2 / g or 5.0m 2 / g, etc.

[0012] Preferably, the tap density of the highly aluminum-doped cobalt hydroxide is 2-3 g / cm 3 , for example 2.0g / cm 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 or 3.0g / cm 3 wait.

[0013] Preferably, the purity of the highly aluminum-doped cobalt hydroxide is above 99.90%, for example, 99.90%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, 99.98% or 99.99%.

[0014] The highly aluminum-doped cobalt hydroxide provided by the present invention has high purity, can further meet market demand, and further improve the performance of the highly aluminum-doped cobalt hydroxide.

[0015] Preferably, the sphericity of the highly aluminum-doped cobalt hydroxide is above 90%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%.

[0016] In a second aspect, the present invention provides a method for preparing the highly aluminum-doped cobalt hydroxide according to the first aspect, the preparation method comprising the following steps:

[0017] (1) pre-treating the cobalt-aluminum mixed solution to obtain a pre-treated cobalt-aluminum mixed solution, wherein the content of magnetic foreign matter in the pre-treated cobalt-aluminum mixed solution is less than 10 ppb;

[0018] (2) Under a protective atmosphere, the pretreated cobalt-aluminum mixed solution and the precipitant solution are flowed into the bottom liquid to perform a coprecipitation reaction to obtain the highly aluminum-doped cobalt hydroxide.

[0019] In the present invention, the content of magnetic foreign matter in the pretreated cobalt-aluminum mixed solution is less than 10 ppb, for example, 10 ppb, 9 ppb, 8 ppb, 7 ppb, 6 ppb, 5 ppb or 4 ppb.

[0020] In the present invention, the "magnetic foreign matter content" refers to the percentage of the mass of the ferromagnetic metal impurity elements in the cobalt-aluminum mixed solution to the total mass of the cobalt-aluminum mixed solution.

[0021] The preparation method of highly aluminum-doped cobalt hydroxide provided by the present invention reduces the content of magnetic foreign matter in the pretreated cobalt-aluminum mixed solution through a pretreatment process of the raw material cobalt-aluminum mixed solution, thereby further improving the morphology and performance of the prepared highly aluminum-doped cobalt hydroxide. Combined with an intermittent synthesis process of a coprecipitation reaction (coprecipitation reaction is carried out while adding raw materials in parallel, and the material is taken out once after the reaction), highly aluminum-doped cobalt hydroxide with high sphericity, high doping amount and uniform doping is prepared, thereby improving the electrochemical performance of the lithium cobalt oxide positive electrode material prepared using the highly aluminum-doped cobalt hydroxide as the raw material when the battery is operated at high voltage.

[0022] Preferably, the pretreatment in step (1) includes removing impurities from the cobalt-aluminum mixed solution.

[0023] Preferably, the impurity removal includes: sequentially performing pressure filtration, microporous filtration and circulating iron removal on the cobalt-aluminum mixed solution.

[0024] Preferably, the equipment used for the pressure filtration includes a filter press to remove foreign matter from the cobalt-aluminum mixed solution.

[0025] Preferably, the equipment used for the microporous filtration includes a microporous precision filter to remove tiny particle impurities in the cobalt-aluminum mixed solution.

[0026] Preferably, the pore size of the microporous precision filter is below 0.5 μm, such as 0.5 μm, 0.1 μm, 0.05 μm or 0.01 μm.

[0027] Preferably, the circulating iron removal further includes filtering with a bag filter.

[0028] Preferably, the content of each impurity metal element in the pretreated cobalt-aluminum mixed solution obtained in step (1) is less than 0.001wt%, for example, 0.001wt%, 0.0008wt%, 0.0006wt%, 0.0004wt%, 0.0002wt%, 0.0001wt%, 0.00008wt%, 0.00006wt%, 0.00004wt%, 0.00002wt% or 0.00001wt%, etc.

[0029] The present invention purifies impurities in the cobalt-aluminum mixed solution after pretreatment, so that the content of impurity metal elements after pretreatment is extremely low. While preparing high-purity and highly aluminum-doped cobalt hydroxide, it can promote the preparation of high-performance and high-sphericity cobalt hydroxide.

[0030] Preferably, the impurity metal elements include any one of copper, iron, nickel, chromium or zinc, or a combination of at least two of them.

[0031] Preferably, the base liquid in step (2) comprises water, an alkaline substance and a complexing agent.

[0032] Preferably, the pH of the base solution in step (2) is 9.3-9.6, such as 9.3, 9.4, 9.5 or 9.6.

[0033] Preferably, the concentration of the complexing agent in the base solution of step (2) is 3-5wt%, for example, 3.0wt%, 3.2wt%, 3.4wt%, 3.6wt%, 3.8wt%, 4.0wt%, 4.2wt%, 4.4wt%, 4.6wt%, 4.8wt% or 5.0wt%, etc.

[0034] Preferably, the alkaline substance comprises sodium hydroxide.

[0035] Preferably, the complexing agent comprises aqueous ammonia.

[0036] Preferably, the cobalt-aluminum mixed solution in step (1) comprises a cobalt source, an aluminum source and a solvent.

[0037] Preferably, the cobalt source comprises cobalt chloride and / or cobalt sulfate.

[0038] Preferably, the aluminum source comprises aluminum chloride and / or aluminum sulfate.

[0039] Preferably, the concentration of cobalt ions in the cobalt-aluminum mixed solution in step (1) is 110-130 g / L, for example, 110 g / L, 112 g / L, 114 g / L, 116 g / L, 118 g / L, 120 g / L, 122 g / L, 124 g / L, 126 g / L, 128 g / L or 130 g / L, etc.

[0040] Preferably, the concentration of aluminum ions in the cobalt-aluminum mixed solution in step (1) is 1.6-1.8 g / L, for example, 1.60 g / L, 1.62 g / L, 1.64 g / L, 1.66 g / L, 1.68 g / L, 1.70 g / L, 1.72 g / L, 1.74 g / L, 1.76 g / L, 1.78 g / L or 1.80 g / L, etc.

[0041] Preferably, the co-current flow rate of the pretreated cobalt-aluminum mixed solution in step (2) is 250-300 L / h, for example, 250 L / h, 255 L / h, 260 L / h, 265 L / h, 270 L / h, 275 L / h, 280 L / h, 285 L / h, 290 L / h, 295 L / h or 300 L / h, etc.

[0042] Preferably, the precipitant solution in step (2) comprises an alkali solution and a complexing agent.

[0043] Preferably, in the precipitant solution, the alkali solution comprises a sodium hydroxide solution.

[0044] Preferably, in the precipitant solution, the complexing agent comprises aqueous ammonia.

[0045] Preferably, in the precipitant solution, the concentration of the alkaline substance in the alkali solution is 30-40wt%, for example, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt% or 40wt%, etc.

[0046] Preferably, in the precipitant solution, the concentration of the complexing agent is 3-5wt%, for example, 3.0wt%, 3.2wt%, 3.4wt%, 3.6wt%, 3.8wt%, 4.0wt%, 4.2wt%, 4.4wt%, 4.6wt%, 4.8wt% or 5.0wt%, etc.

[0047] Preferably, the co-current flow rate of the precipitant solution in step (2) is 100-125 L / h, for example, 100 L / h, 102 L / h, 104 L / h, 106 L / h, 108 L / h, 110 L / h, 112 L / h, 114 L / h, 116 L / h, 118 L / h, 120 L / h, 122 L / h, 124 L / h or 125 L / h, etc.

[0048] Preferably, the protective atmosphere in step (2) includes nitrogen atmosphere and / or inert atmosphere.

[0049] Preferably, the gas in the inert atmosphere includes any one of argon, helium or neon.

[0050] Preferably, the flow rate of the gas in the protective atmosphere in step (2) is 10-15m 3 / h, for example 10m 3 / h、11m 3 / h、12m 3 / h、13m 3 / h、14m 3 / h or 15m 3 / h, etc.

[0051] Preferably, the pH of the coprecipitation reaction in step (2) is 9.6-9.8, such as 9.6, 9.7 or 9.8.

[0052] Preferably, during the coprecipitation reaction in step (2), the product grain growth rate is controlled to be 0.3-1 μm / h, for example, 0.3 μm / h, 0.4 μm / h, 0.5 μm / h, 0.6 μm / h, 0.7 μm / h, 0.8 μm / h, 0.9 μm / h or 1.0 μm / h, etc.

[0053] The present invention controls the growth rate of product grains within a specific range by controlling the flow rate of co-flowing raw materials and the reaction rate, thereby increasing the tap density of spherical highly aluminum-doped cobalt hydroxide. Meanwhile, the generation of new seed crystals is avoided, the normal distribution of the particle size of the obtained product is improved, and the morphology and particle size distribution uniformity of the obtained highly aluminum-doped cobalt hydroxide are optimized.

[0054] Preferably, the coprecipitation reaction time in step (2) is 120-200 h, for example, 120 h, 130 h, 140 h, 150 h, 160 h, 170 h, 180 h, 190 h or 200 h.

[0055] Preferably, after the coprecipitation reaction in step (2), the product of the coprecipitation reaction is separated and filtered and washed.

[0056] Preferably, the filter press washing is performed until the concentration of impurity ions in the washing liquid is below 20 ppm, for example, 20 ppm, 18 ppm, 16 ppm, 14 ppm, 12 ppm or 10 ppm.

[0057] Preferably, the impurity ions include sodium ions and / or chloride ions.

[0058] Preferably, the product is dried after the filter pressing and washing.

[0059] Preferably, the drying method includes nitrogen purging.

[0060] Preferably, the drying is performed until the water content of the dried product is 0.5-1.0 wt%, such as 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1.0 wt%.

[0061] In a third aspect, the present invention provides an aluminum-doped cobalt oxide, wherein the aluminum-doped cobalt oxide is prepared using the highly aluminum-doped cobalt hydroxide described in the first aspect.

[0062] Preferably, the aluminum-doped cobalt trioxide is prepared by the following preparation method, comprising:

[0063] The aluminum-doped cobalt trioxide is obtained by calcining the highly aluminum-doped cobalt hydroxide as described in the first aspect.

[0064] Preferably, the calcination temperature is 500-600°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C.

[0065] Preferably, the calcination time is 3-8 h, such as 3 h, 4 h, 5 h, 6 h, 7 h or 8 h.

[0066] In a fourth aspect, the present invention provides a positive electrode material, which is prepared using the aluminum-doped cobalt tetroxide described in the third aspect.

[0067] Preferably, the method for preparing the positive electrode material comprises the following steps:

[0068] The aluminum-doped cobalt tetroxide described in the third aspect is mixed with a lithium source and calcined to obtain the positive electrode material.

[0069] Preferably, the molar ratio of the aluminum-doped cobalt oxide to the lithium source is 1:(1-1.2), for example, 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2.

[0070] Preferably, the calcination temperature is 800-900°C, for example, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C.

[0071] Compared with the prior art, the present invention has at least the following beneficial effects:

[0072] (1) The morphology of the highly aluminum-doped cobalt hydroxide provided by the present invention is a spherical structure, which can effectively improve the stacking performance and structural stability of cobalt hydroxide, maintain the morphological integrity of the subsequently prepared cobalt oxide, avoid particle breakage and agglomeration, easily form a more compact electrode structure, and reduce the occurrence of side reactions between the electrode material and the electrolyte, thereby improving the energy density and cycle stability of the cobalt carbonate positive electrode material. On the other hand, the highly aluminum-doped cobalt hydroxide provided by the present invention has a high aluminum content, which can promote the formation of a more stable lattice structure, slow down the volume change and phase change of the positive electrode material prepared by the subsequent process during the battery charge and discharge process, improve the cycle life of the positive electrode material, and optimize the electron / ion transmission path of the positive electrode material, thereby improving the cycle performance of the battery at high voltage.

[0073] (2) The preparation method of highly aluminum-doped cobalt hydroxide provided by the present invention reduces the content of magnetic foreign matter in the pretreated cobalt-aluminum mixed solution through a pretreatment process of the raw material cobalt-aluminum mixed solution, which can further improve the morphology and performance of the prepared highly aluminum-doped cobalt hydroxide. Combined with the intermittent synthesis process of the coprecipitation reaction, highly aluminum-doped cobalt hydroxide with high sphericity, high doping amount and uniform doping can be prepared, thereby improving the electrochemical performance of the lithium cobalt oxide positive electrode material prepared using highly aluminum-doped cobalt hydroxide as raw material when the battery is operated at high voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 This is a scanning electron microscope image (SEM) of the highly aluminum-doped cobalt hydroxide (after 156 hours of coprecipitation reaction) obtained by the preparation method provided in Example 1 of the present invention.

[0075] Figure 2 This is a scanning electron microscope image (SEM) of the product obtained by the preparation method provided in Example 1 of the present invention after 108 hours of coprecipitation reaction.

[0076] Figure 3 This is a scanning electron microscope image (SEM) of the product obtained by the preparation method provided in Example 1 of the present invention after 68 hours of coprecipitation reaction.

[0077] Figure 4 This is a scanning electron microscope image (SEM) of the product obtained by the preparation method provided in Example 1 of the present invention after 36 hours of coprecipitation reaction.

[0078] Figure 5 This is a scanning electron microscope (SEM) image of aluminum-doped cobalt tetroxide provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0079] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0080] The manufacturer and model of the filter press used in the following examples is Jingjin XAGZ100 / 1000-UK, the manufacturer and model of the microporous precision filter is Eastern Europe DO-PGRF-150B, wherein the internal filter mesh pore size is 0.5 μm, and the manufacturer and model of the bag filter is Boyue YF-220PPR-2#S.

[0081] Example 1

[0082] This embodiment provides a method for preparing highly aluminum-doped cobalt hydroxide, comprising the following steps:

[0083] S1. Add water to cobalt chloride hexahydrate and anhydrous aluminum chloride to prepare a cobalt-aluminum mixed solution, wherein the concentration of cobalt ions in the cobalt-aluminum mixed solution is 120 g / L, and the concentration of aluminum ions in the cobalt-aluminum mixed solution is 1.7 g / L; then, use a filter press to remove foreign matter from the cobalt-aluminum mixed solution, and then use a microporous precision filter to remove tiny particle impurities, and then circulate iron removal and bag filter filtration between storage tanks to obtain a pretreated cobalt-aluminum mixed solution, wherein the content of magnetic foreign matter in the pretreated cobalt-aluminum mixed solution is 8 ppb, and the content of each impurity metal element of copper, iron, nickel, chromium and zinc is less than 0.001 wt%.

[0084] S2. The flow rate into the reactor is 15m 3 / h of nitrogen as a protective gas, and at the same time, the pretreated cobalt-aluminum mixed solution and the precipitant solution obtained in step S1 are flowed into a reactor containing a bottom liquid to carry out a coprecipitation reaction, the pH of the reaction system during the coprecipitation reaction is maintained at 9.7, the co-flow rate of the cobalt-aluminum mixed solution is 270L / h, the co-flow rate of the precipitant solution is 110L / h, the precipitant solution includes sodium hydroxide solution and ammonia water, the concentration of sodium hydroxide in the precipitant solution is 35wt%, the concentration of ammonia water in the precipitant solution is 4wt%, the bottom liquid in the reactor includes water, sodium hydroxide and ammonia water, wherein the pH in the bottom liquid is 9.5, the concentration of ammonia water in the bottom liquid is 3.5wt%, the grain growth rate in the reactor is controlled to be 0.5μm / h during the coprecipitation reaction, and the reaction is stopped after 158h of the coprecipitation reaction.

[0085] S3. The product obtained after the coprecipitation reaction is subjected to solid-liquid separation, and the solid product is filtered and washed until the concentrations of chloride ions and sodium ions in the washing liquid are both less than 20 ppm. Then, the washed product is dried using nitrogen purge until the water content of the dried product is 0.6 wt % to obtain highly aluminum-doped cobalt hydroxide. The highly aluminum-doped cobalt hydroxide obtained comprises cobalt hydroxide and aluminum doped in the cobalt hydroxide. The highly aluminum-doped cobalt hydroxide has a spherical morphology and an aluminum doping content of 10,000 ppm.

[0086] This embodiment also provides a method for preparing aluminum-doped cobalt tetroxide, comprising the following steps:

[0087] The highly aluminum-doped cobalt hydroxide prepared by the above preparation method was placed in a push plate kiln and calcined at 580° C. for 5 hours to obtain aluminum-doped cobalt tetroxide.

[0088] Example 2

[0089] This embodiment provides a method for preparing highly aluminum-doped cobalt hydroxide, comprising the following steps:

[0090] S1. Add water to cobalt sulfate and aluminum sulfate to prepare a cobalt-aluminum mixed solution, wherein the concentration of cobalt ions in the cobalt-aluminum mixed solution is 120 g / L, and the concentration of aluminum ions in the cobalt-aluminum mixed solution is 1.6 g / L; then, use a filter press to remove foreign matter from the cobalt-aluminum mixed solution, and then use a microporous precision filter to remove tiny particle impurities, and then circulate iron removal and bag filter filtration between storage tanks to obtain a pretreated cobalt-aluminum mixed solution. The content of magnetic foreign matter in the pretreated cobalt-aluminum mixed solution is 10 ppb, and the content of each impurity metal element of copper, iron, nickel, chromium and zinc is less than 0.001 wt%.

[0091] S2. The flow rate into the reactor is 10m 3 / h of nitrogen as a protective gas, and at the same time, the pretreated cobalt-aluminum mixed solution and the precipitant solution obtained in step S1 are flowed into a reactor containing a bottom liquid to carry out a coprecipitation reaction, the pH of the reaction system during the coprecipitation reaction is maintained at 9.6, the co-flow rate of the cobalt-aluminum mixed solution is 250L / h, the co-flow rate of the precipitant solution is 100L / h, the precipitant solution includes sodium hydroxide solution and ammonia water, the concentration of sodium hydroxide in the precipitant solution is 30wt%, the concentration of ammonia water in the precipitant solution is 3wt%, the bottom liquid in the reactor includes water, sodium hydroxide and ammonia water, wherein the pH in the bottom liquid is 9.3, the concentration of ammonia water in the bottom liquid is 4.0wt%, the grain growth rate in the reactor is controlled to be 0.3μm / h during the coprecipitation reaction, and the reaction is stopped after 120h of the coprecipitation reaction.

[0092] S3. The product obtained after the coprecipitation reaction is subjected to solid-liquid separation, and the solid product is filtered and washed until the concentrations of sulfate ions and sodium ions in the washing liquid are both less than 15 ppm. Then, the washed product is dried using nitrogen purge until the water content of the dried product is 0.5 wt % to obtain highly aluminum-doped cobalt hydroxide. The highly aluminum-doped cobalt hydroxide obtained comprises cobalt hydroxide and aluminum doped in the cobalt hydroxide. The highly aluminum-doped cobalt hydroxide has a spherical morphology and an aluminum doping content of 9600 ppm.

[0093] This embodiment also provides a method for preparing aluminum-doped cobalt tetroxide, comprising the following steps:

[0094] The highly aluminum-doped cobalt hydroxide prepared by the above preparation method is placed in a push plate kiln and calcined at 500° C. for 8 hours to obtain aluminum-doped cobalt tetroxide.

[0095] Example 3

[0096] This embodiment provides a method for preparing highly aluminum-doped cobalt hydroxide, comprising the following steps:

[0097] S1. Add water to cobalt chloride hexahydrate and anhydrous aluminum chloride to prepare a cobalt-aluminum mixed solution, wherein the concentration of cobalt ions in the cobalt-aluminum mixed solution is 130 g / L, and the concentration of aluminum ions in the cobalt-aluminum mixed solution is 1.7 g / L; then, use a filter press to remove foreign matter from the cobalt-aluminum mixed solution, and then use a microporous precision filter to remove tiny particle impurities, and then circulate iron removal and bag filter filtration between storage tanks to obtain a pretreated cobalt-aluminum mixed solution, wherein the content of magnetic foreign matter in the pretreated cobalt-aluminum mixed solution is 7 ppb, and the content of each impurity metal element of copper, iron, nickel, chromium and zinc is less than 0.001 wt%.

[0098] S2. The flow rate into the reactor is 15m 3 / h of nitrogen as a protective gas, and at the same time, the pretreated cobalt-aluminum mixed solution and the precipitant solution obtained in step S1 are flowed into a reactor containing a bottom liquid to carry out a coprecipitation reaction, the pH of the reaction system during the coprecipitation reaction is maintained at 9.8, the co-flow rate of the cobalt-aluminum mixed solution is 300L / h, the co-flow rate of the precipitant solution is 125L / h, the precipitant solution includes sodium hydroxide solution and ammonia water, the concentration of sodium hydroxide in the precipitant solution is 40wt%, the concentration of ammonia water in the precipitant solution is 5wt%, the bottom liquid in the reactor includes water, sodium hydroxide and ammonia water, wherein the pH in the bottom liquid is 9.6, the concentration of ammonia water in the bottom liquid is 4.5wt%, the grain growth rate in the reactor is controlled to be 1μm / h during the coprecipitation reaction, and the reaction is stopped after 200h of the coprecipitation reaction.

[0099] S3. The product obtained after the coprecipitation reaction is subjected to solid-liquid separation, and the solid product is filtered and washed until the concentrations of chloride ions and sodium ions in the washing liquid are both less than 18 ppm. Then, the washed product is dried using nitrogen purge until the water content of the dried product is 1.0 wt% to obtain highly aluminum-doped cobalt hydroxide. The highly aluminum-doped cobalt hydroxide obtained comprises cobalt hydroxide and aluminum doped in the cobalt hydroxide. The highly aluminum-doped cobalt hydroxide has a spherical morphology and an aluminum doping content of 9400 ppm.

[0100] This embodiment also provides a method for preparing aluminum-doped cobalt tetroxide, comprising the following steps:

[0101] The highly aluminum-doped cobalt hydroxide prepared by the above preparation method is placed in a push plate kiln and calcined at 600° C. for 5 hours to obtain aluminum-doped cobalt tetroxide.

[0102] Example 4

[0103] The only difference between this embodiment and embodiment 1 is that in the preparation method of highly aluminum-doped cobalt hydroxide provided in this embodiment, the concentration of aluminum ions in the cobalt-aluminum mixed solution prepared in step S1 is 1.5 g / L. The rest of the contents are the same as those in embodiment 1.

[0104] Example 5

[0105] The only difference between this embodiment and embodiment 1 is that in the preparation method of highly aluminum-doped cobalt hydroxide provided in this embodiment, the concentration of aluminum ions in the cobalt-aluminum mixed solution prepared in step S1 is 1.8 g / L. The rest of the contents are the same as those in embodiment 1.

[0106] Example 6

[0107] This embodiment differs from Example 1 only in that, in the method for preparing highly aluminum-doped cobalt hydroxide provided in this embodiment, step S2 controls the flow rate of the co-flowing raw materials and the reaction rate to control the grain growth rate in the reactor during the co-precipitation reaction to 0.1 μm / h. All other details are the same as in Example 1.

[0108] Example 7

[0109] This embodiment differs from Example 1 only in that, in the method for preparing highly aluminum-doped cobalt hydroxide provided in this embodiment, step S2 controls the flow rate of the co-flowing raw materials and the reaction rate to control the grain growth rate in the reactor during the co-precipitation reaction to 1.2 μm / h. All other details are the same as in Example 1.

[0110] Example 8

[0111] The only difference between this embodiment and embodiment 1 is that in the method for preparing highly aluminum-doped cobalt hydroxide provided in this embodiment, the water content of the product dried in step S3 is 0.3 wt %. The rest of the contents are the same as those in embodiment 1.

[0112] Example 9

[0113] The only difference between this embodiment and embodiment 1 is that in the method for preparing highly aluminum-doped cobalt hydroxide provided in this embodiment, the water content of the product dried in step S3 is 1.2 wt %. The rest of the contents are the same as those in embodiment 1.

[0114] Example 10

[0115] The only difference between this embodiment and embodiment 1 is that the preparation method of highly aluminum-doped cobalt hydroxide provided in this embodiment adopts a non-intermittent preparation process, that is, the preparation process of step S2 is replaced by: pre-filling the reactor with finished cobalt hydroxide material, and then introducing a flow rate of 15m 3 / h of nitrogen as a protective gas, and simultaneously the pretreated cobalt-aluminum mixed solution and the precipitant solution are flowed in parallel into a reactor containing a bottom liquid to carry out a coprecipitation reaction. The pH of the reaction system during the coprecipitation reaction is maintained at 9.7, the co-flow rate of the cobalt-aluminum mixed solution is 270L / h, and the co-flow rate of the precipitant solution is 110L / h. The precipitant solution includes a sodium hydroxide solution and aqueous ammonia, the concentration of the sodium hydroxide in the precipitant solution is 35wt%, and the concentration of the aqueous ammonia in the precipitant solution is 4wt%. During the reaction process, the product prepared by the coprecipitation reaction is taken out at the overflow port while feeding, and then the process of step S3 is continuously carried out on the obtained product. The remaining contents are the same as those in Example 1.

[0116] Example 11

[0117] This embodiment differs from Example 1 only in that, in the method for preparing highly aluminum-doped cobalt hydroxide provided in this embodiment, step S1 utilizes only a filter press to remove foreign matter from the cobalt-aluminum mixed solution, omitting the use of a microporous precision filter to remove minute particle impurities, and omitting the circulating iron removal and bag filter filtration between storage tanks. All other details are the same as in Example 1.

[0118] Comparative Example 1

[0119] The only difference between this comparative example and Example 1 is that in the preparation method provided in this comparative example, the addition of anhydrous aluminum chloride in step S1 is omitted to prepare pure cobalt hydroxide material. The rest of the contents are the same as in Example 1.

[0120] Comparative Example 2

[0121] The only difference between this comparative example and Example 1 is that the preparation method of highly aluminum-doped cobalt hydroxide provided in this comparative example omits the entire process of pre-treating the cobalt-aluminum mixed solution in step S1. The rest of the contents are the same as in Example 1.

[0122] The sphericity, specific surface area, tap density and purity of the highly aluminum-doped cobalt hydroxide or pure cobalt hydroxide materials prepared in Examples 1-11 and Comparative Examples 1-2 were tested. The specific testing process is as follows:

[0123] (1) Sphericity: Scanning electron microscopy (SEM) or transmission electron microscopy (TEM) imaging analysis is performed, and the roundness or aspect ratio of the particles is calculated using image processing software (such as ImageJ). The proportion of particles that meet the spherical standard (roundness > 0.9) is counted.

[0124] (2) Specific surface area test: The Brunauer-Emmett-Teller (BET) nitrogen adsorption method was used according to GB / T19587. After the sample was degassed at 150 °C for 4 h, the adsorption isotherm was measured at 77 K to calculate the specific surface area.

[0125] (3) Tap density test: According to GB / T 5162, a tap density meter was used. 5 g of sample was placed in a graduated test tube and vibrated at a frequency of 250 times per minute until the volume remained constant. The mass / volume ratio was then calculated.

[0126] (4) Purity test: Principal component analysis: Inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the content of Co, Al elements and residual impurity metals (such as Ni, Cu, Fe, Cr, Zn), and residual anions: Ion chromatography (IC) to detect OH - 、SO4 2- 、Cl - Impurities such as water and volatile matter: dry in an oven at 105°C to constant weight, and calculate the weight loss rate.

[0127] The test results are shown in Table 1:

[0128] Table 1

[0129] Sphericity (%) <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Tap density (g / cm 3 )]]> purity(%) Example 1 98 3.16 2.32 99.98 Example 2 97 3.05 2.28 99.97 Example 3 96 2.98 2.25 99.96 Example 4 95 2.90 2.20 99.95 Example 5 94 2.85 2.18 99.94 Example 6 93 2.80 2.15 99.93 Example 7 92 2.75 2.12 99.92 Example 8 97 3.00 2.25 99.97 Example 9 96 2.95 2.22 99.96 Example 10 95 2.90 2.18 99.95 Example 11 90 2.65 2.05 99.90 Comparative Example 1 85 2.50 1.90 99.85 Comparative Example 2 80 2.30 1.80 99.80

[0130] The aluminum-doped cobalt oxide obtained in the above Examples 1-11 and Comparative Examples 1-2 was mixed with lithium hydroxide in a molar ratio of 1:1.05 and calcined at 850°C for 12 hours to obtain a lithium cobalt oxide positive electrode material. The obtained lithium cobalt oxide positive electrode material was uniformly mixed with a polyvinylidene fluoride (PVDF) binder, conductive carbon black and N-methylpyrrolidone in a mass ratio of 90:5:5 to obtain a mixed slurry. The mixed slurry was coated on a current collector to form a positive electrode sheet, which was assembled into a lithium ion battery together with a metal lithium negative electrode sheet, a polypropylene (PP) separator, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) (volume ratio of 1:1:1).

[0131] The energy density and cycle stability of the lithium-ion battery assembled above were tested. The specific test process is as follows:

[0132] (1) Energy density test: The assembled lithium-ion battery was left to stand for 24 h to allow the electrolyte to fully infiltrate the electrode material. A blue battery test system was used to perform charge and discharge tests at room temperature with a current density of 0.1 C. The charge cut-off voltage was 4.35 V, and the discharge cut-off voltage was 3.0 V. The charge capacity and discharge capacity of the battery were recorded. The energy density of the battery was calculated according to the formula E = U × C (where E is the energy density, U is the average discharge voltage, and C is the discharge specific capacity). Three parallel batteries were tested for each sample, and the average value was taken as the final result.

[0133] (2) Cycling stability: At room temperature, the battery was subjected to a charge and discharge cycle test using a constant current charge and discharge mode at a current density of 1C. The charge cut-off voltage was 4.35V and the discharge cut-off voltage was 3.0V. The discharge capacity was recorded after each charge and discharge cycle. The cycle test was repeated 100 times, and the capacity retention rate of the battery at the 100th cycle was calculated using the following formula: Capacity retention rate (%) = C 100 / C1×100%, where C1 is the first discharge capacity, C 100 The 100th discharge capacity is obtained. Similarly, three parallel batteries are tested for each sample, and the average value is taken as the final result.

[0134] The test results are shown in Table 2.

[0135] Table 2

[0136]

[0137]

[0138] The test results show that:

[0139] (1) It can be seen from Examples 1 to 3 that the highly aluminum-doped cobalt hydroxide provided by the present invention has the advantages of a spherical morphology and a high aluminum content, which work together to improve the electrochemical cycling performance of the positive electrode material prepared using highly aluminum-doped cobalt hydroxide as a raw material when the battery is operated at high voltage.

[0140] Figure 1 A scanning electron microscope (SEM) image of the highly aluminum-doped cobalt hydroxide obtained by the preparation method provided in Example 1 (after 156 hours of coprecipitation reaction) is given. As can be seen from the image, the highly aluminum-doped cobalt hydroxide prepared by the preparation method provided by the present invention has a spherical structure and the particles are uniform in size.

[0141] Figure 2 、 Figure 3 and Figure 4 The scanning electron micrographs (SEM) of the products obtained by the preparation method provided in Example 1 after 108h, 68h and 36h of coprecipitation reaction are respectively given. Figure 2-Figure 4It can be seen that as the reaction time progresses, the crystals become larger and larger, the surface becomes smoother and smoother, and the sphericity gradually increases.

[0142] Figure 5 A scanning electron microscope (SEM) image of the aluminum-doped cobalt oxide provided in Example 1 is provided. As can be seen from the image, the aluminum-doped cobalt oxide prepared by the highly aluminum-doped sodium hydroxide provided by the present invention still maintains a good spherical morphology and good particle uniformity.

[0143] (2) By comparing Example 1 with Examples 4-5, it can be seen that if the concentration of aluminum ions in the prepared cobalt-aluminum mixed solution of the present invention is too low, the aluminum content in the obtained aluminum-doped cobalt hydroxide will decrease, thereby affecting the electrochemical performance of the positive electrode material under high voltage; if the concentration of aluminum ions in the prepared cobalt-aluminum mixed solution is too high, the battery capacity will decrease.

[0144] (3) By comparing Example 1 with Examples 6-7, it can be seen that if the grain growth rate in the reactor during the coprecipitation reaction of the present invention is too slow, the reaction cycle will be increased, the frequency of defects will be increased, and new crystal seeds will be easily formed in the later stage of the reaction, resulting in a decrease in the normal distribution of the particles, thereby causing the electrochemical performance of the subsequently prepared positive electrode material under high voltage to decrease; if the grain growth rate in the reactor during the coprecipitation reaction is too fast, the formed spherical grains will be loose, and the tap density of the obtained highly aluminum-doped cobalt hydroxide will be low, thereby affecting the electrochemical performance of the subsequently prepared positive electrode material under high voltage.

[0145] (4) By comparing Example 1 with Examples 8-9, it can be seen that if the water content of the highly aluminum-doped cobalt hydroxide after drying is too low or too high, it will lead to poor heating uniformity in the subsequent cobalt tetroxide preparation process, thereby affecting the electrochemical performance of the resulting positive electrode material.

[0146] (5) By comparing Example 1 with Example 10, it can be seen that compared with the non-batch preparation process, the highly aluminum-doped cobalt hydroxide prepared by the batch preparation process of the present invention, which adds the raw materials in parallel while performing the coprecipitation reaction and removes the product all at once after the reaction, has the advantages of better sphericity and higher tap density.

[0147] (6) By comparing Example 1 and Example 11, it can be seen that if the present invention only uses a filter press to remove foreign matter from the cobalt-aluminum mixed solution, a large amount of impurities will be present in the co-flown cobalt-aluminum mixed solution, and the content of magnetic foreign matter will be relatively high, thereby causing the electrochemical performance of the battery at high voltage to decrease, and even causing safety problems when the battery is subsequently operated for a long time.

[0148] (7) By comparing Example 1 with Comparative Example 1, it can be seen that compared with conventional cobalt hydroxide, the highly aluminum-doped cobalt hydroxide provided by the present invention has a more excellent spherical morphology and structural stability, and the material has a higher tap density and purity, which can improve the electrochemical performance of the obtained positive electrode material at high voltage.

[0149] (8) By comparing Example 1 and Comparative Example 2, it can be seen that if the pretreatment process of step S1 is directly omitted in the present invention, the cobalt content of the product will be reduced, the electrochemical performance of the subsequently assembled battery will be reduced, and the safety risk of the battery will be increased.

[0150] In summary, the morphology of the highly aluminum-doped cobalt hydroxide provided by the present invention is a spherical structure, which can effectively improve the stacking performance and structural stability of cobalt hydroxide, maintain the morphological integrity of the subsequently prepared cobalt trioxide, avoid particle breakage and agglomeration, easily form a more compact electrode structure, and can reduce the occurrence of side reactions between the electrode material and the electrolyte, thereby improving the energy density and cycle stability of the cobalt carbonate positive electrode material. On the other hand, the aluminum content in the highly aluminum-doped cobalt hydroxide provided by the present invention is high, which can promote the formation of a more stable lattice structure, reduce the volume change and phase change of the positive electrode material prepared by the subsequent process during the battery charge and discharge process, improve the cycle life of the positive electrode material, and optimize the electron / ion transmission path of the positive electrode material, thereby improving the cycle performance of the battery at high voltage. The spherical morphology of the highly aluminum-doped cobalt hydroxide provided by the present invention and the advantages of high aluminum content synergistically improve the electrochemical cycle performance of the positive electrode material prepared with highly aluminum-doped cobalt hydroxide as raw material when the battery is running at high voltage.

[0151] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A highly aluminum-doped cobalt hydroxide, characterized in that: The highly aluminum-doped cobalt hydroxide comprises cobalt hydroxide and aluminum elements doped in the cobalt hydroxide. The highly aluminum-doped cobalt hydroxide has a spherical morphology and an aluminum doping amount of 9000-10000 ppm.

2. The highly aluminum-doped cobalt hydroxide according to claim 1, characterized in that The specific surface area of ​​the highly aluminum-doped cobalt hydroxide is 2-5 m 2 / g; Preferably, the tap density of the highly aluminum-doped cobalt hydroxide is 2-3 g / cm 3 ; Preferably, the purity of the highly aluminum-doped cobalt hydroxide is above 99.90%; Preferably, the sphericity of the highly aluminum-doped cobalt hydroxide is above 90%.

3. A method for preparing highly aluminum-doped cobalt hydroxide according to any one of claims 1 or 2, characterized in that: The preparation method comprises the following steps: (1) pre-treating the cobalt-aluminum mixed solution to obtain a pre-treated cobalt-aluminum mixed solution, wherein the content of magnetic foreign matter in the pre-treated cobalt-aluminum mixed solution is less than 10 ppb; (2) Under a protective atmosphere, the pretreated cobalt-aluminum mixed solution and the precipitant solution are flowed into the bottom liquid to perform a coprecipitation reaction to obtain the highly aluminum-doped cobalt hydroxide.

4. The preparation method according to claim 3, characterized in that The pretreatment in step (1) includes removing impurities from the cobalt-aluminum mixed solution; Preferably, the impurity removal comprises: sequentially performing pressure filtration, microfiltration and cyclic iron removal on the cobalt-aluminum mixed solution; Preferably, the content of each impurity metal element in the pretreated cobalt-aluminum mixed solution obtained in step (1) is less than 0.001 wt%; Preferably, the impurity metal elements include any one of copper, iron, nickel, chromium or zinc, or a combination of at least two of them.

5. The preparation method according to claim 3 or 4, characterized in that The cobalt-aluminum mixed solution in step (1) comprises a cobalt source, an aluminum source and a solvent; Preferably, the concentration of cobalt ions in the cobalt-aluminum mixed solution in step (1) is 110-130 g / L; Preferably, the concentration of aluminum ions in the cobalt-aluminum mixed solution in step (1) is 1.6-1.8 g / L.

6. The preparation method according to any one of claims 3 to 5, characterized in that The co-current flow rate of the pretreated cobalt-aluminum mixed solution in step (2) is 250-300 L / h; Preferably, the precipitant solution in step (2) comprises an alkali solution and a complexing agent; Preferably, in the precipitant solution, the concentration of the alkaline substance in the alkali solution is 30-40 wt%; Preferably, in the precipitant solution, the concentration of the complexing agent is 3-5 wt%; Preferably, the co-current flow rate of the precipitant solution in step (2) is 100-125 L / h.

7. The preparation method according to any one of claims 3 to 6, characterized in that The protective atmosphere in step (2) includes nitrogen atmosphere and / or inert atmosphere; Preferably, the flow rate of the gas in the protective atmosphere in step (2) is 10-15m 3 / h; Preferably, the pH of the coprecipitation reaction in step (2) is 9.6-9.8; Preferably, the product grain growth rate is controlled to be 0.3-1 μm / h during the coprecipitation reaction in step (2); Preferably, the coprecipitation reaction time in step (2) is 120-200 hours.

8. The preparation method according to any one of claims 3 to 7, characterized in that After the coprecipitation reaction in step (2), the product of the coprecipitation reaction is separated and filtered and washed; Preferably, the filter press washing is performed until the concentration of impurity ions in the washing liquid is below 20 ppm; Preferably, the product is dried after the filter pressing and washing; Preferably, the drying method includes nitrogen purging; Preferably, the drying is performed until the moisture content of the dried product is 0.5-1.0 wt%.

9. An aluminum-doped cobalt trioxide, characterized in that: The aluminum-doped cobalt trioxide is prepared using the highly aluminum-doped cobalt hydroxide as claimed in claim 1 or 2.

10. A positive electrode material, characterized in that The positive electrode material is prepared by using the aluminum-doped cobalt tetroxide as claimed in claim 9.

Images