Carbonic acid system aluminum-doped cobaltosic oxide as well as preparation method and application thereof

Abstract

The invention provides a preparation method of carbonic acid system aluminum-doped cobaltosic oxide, which comprises the following steps: firstly, respectively preparing a cobalt salt solution, an ammonium bicarbonate solution and an aluminum salt solution; secondly, adding the solution into a reaction container containing a base solution in a parallel flow manner, and controlling the reaction temperature, the pH value of the system and the stirring rotating speed to obtain a first cobalt carbonate wet material; the first cobalt carbonate wet material enters a thickener through an overflow tank to be separated, and clear liquid and sediment are obtained; feeding the precipitate into the reaction container for continuous reaction, and controlling the growth speed of crystal grains to obtain a second cobalt carbonate wet material; and finally, washing, drying and calcining the second cobalt carbonate wet material to obtain the aluminum-doped cobaltosic oxide. The prepared product has the advantages of being good in sphericity degree, high in specific surface area and tap density, good in aluminum element doping uniformity and the like, the selected raw materials are common raw materials and are easy to obtain, the method is easy to operate, industrial production is easy, and the method has wide popularization and application prospects in lithium ion positive electrode materials.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode materials, and specifically relates to a carbonate system aluminum-doped cobalt tetroxide and a preparation method thereof, and also relates to the application of the carbonate system aluminum-doped cobalt tetroxide. Background Art

[0002] Lithium-ion batteries made with lithium cobalt oxide as the positive electrode material have the characteristics of light weight, large capacity, high specific energy, good cycle performance and long life. They occupy a monopoly position in 3C portable electronic products such as smart phones and laptops, and are still in an irreplaceable position.

[0003] As a precursor of lithium cobalt oxide, the performance of cobalt oxide has a direct impact on the performance of lithium cobalt oxide materials. In the prior art, aluminum doping is usually used to improve the voltage and capacity of lithium cobalt oxide, of which there are mainly two methods: solid phase doping and wet doping. Since the solid phase doping method is relatively expensive and easily causes uneven distribution of aluminum in lithium cobalt oxide, resulting in rapid capacity decay, the wet doping method is usually used. This method first uses a coprecipitation method to synthesize aluminum-doped cobalt carbonate, and then the synthesized doped cobalt carbonate is calcined at high temperature to become aluminum-doped cobalt oxide, and finally mixed with lithium carbonate and calcined into doped lithium cobalt oxide. However, the existing preparation process of aluminum-doped cobalt oxide often has the problem of uneven aluminum doping, which will affect the cycle performance and rate performance of the prepared lithium cobalt oxide material.

[0004] Based on this, it is a technical problem that needs to be solved urgently to provide an aluminum-doped cobalt tetroxide with good sphericity, high specific surface area and tap density, and good uniformity of aluminum doping and a preparation method thereof. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing aluminum-doped cobalt tetroxide with good sphericity, high specific surface area and tap density, and good uniformity of aluminum doping.

[0006] The second object of the present invention is to provide an aluminum-doped cobalt tetroxide with good sphericity, high specific surface area and tap density, and good uniformity of aluminum doping.

[0007] The third object of the present invention is to provide an application of aluminum-doped cobalt tetroxide in lithium ion positive electrode materials.

[0008] The technical solution adopted by the present invention to achieve one of the purposes is: to provide a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: S1, respectively preparing a cobalt salt solution with a cobalt ion concentration of 110-140 g / L, an ammonium bicarbonate solution with a concentration of 180-260 g / L, and an aluminum salt solution with an aluminum ion concentration of 2-9 g / L; S2, adding the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution in parallel to the reaction vessel containing the base liquid, reacting for 30-40 hours at a temperature of 40-45° C., a pH value of 7.1-7.6 and a stirring speed of 100-120 r / min to obtain a first cobalt carbonate wet material; S3, the first cobalt carbonate wet material in the reaction container enters a thickener through an overflow tank for separation to obtain a clear liquid and a precipitate; the precipitate enters a reaction container for further reaction to obtain a second cobalt carbonate wet material with a seed particle size of 19.5-19.8 μm; S4. The second cobalt carbonate wet material is washed, dried and calcined to obtain aluminum-doped cobalt tetroxide.

[0009] In the present invention, in order to prepare a carbonate system doped aluminum cobalt tetroxide with good sphericity, high specific surface area and tap density, and good uniformity of aluminum doping, the following improvements are mainly made in the preparation method: Firstly, the present invention prepares a cobalt salt solution, an aluminum salt solution and an ammonium bicarbonate solution respectively, feeds the three at the same time, controls the pH value of the system by adjusting the flow rate of the ammonium bicarbonate solution, and flexibly regulates the amount of aluminum doping by adjusting the feed flow rates of the cobalt salt solution and the aluminum salt solution.

[0010] Secondly, during the reaction stage, the pH, reaction temperature and stirring speed of the reaction system are optimized and adjusted to achieve the control of the growth rate and growth process of the seed crystal particle size and ensure the quality of the product. A large number of studies have found that when the pH of the reaction system is too low, it will lead to secondary particle agglomeration and abnormal particle morphology defects; when the pH is too high, it will lead to reduced uniformity of aluminum doping and the appearance of aluminum segregation. For the stirring speed, when the stirring speed is too low, it will lead to serious particle agglomeration, poor sphericity and dispersibility of cobalt tetroxide particles; and when the stirring speed is too high, it will lead to the appearance of small particles in the subsequent growth process. For the reaction temperature, when the reaction temperature is too high, it will aggravate the volatilization of ammonium bicarbonate in the system, reduce the metal complexation amount of the system, and is not conducive to the growth of the seed crystal; when the reaction temperature is too low, the ion diffusion rate is low, which will slow down the growth of the precursor. Under the condition of low stirring speed, the local metal ion concentration at the feed port will be too high, resulting in local explosive nucleation. Taking the above factors into consideration, in steps S2 and S3 of the present invention, the pH value of the reaction system is set to 7.1-7.6, the stirring speed is set to 100-120 r / min, and the reaction temperature is set to 40-45°C to ensure that the obtained product has better sphericity, better specific surface area and tap density.

[0011] Finally, in the middle stage of the reaction of the present invention, the first cobalt carbonate wet material is treated with a thickener. On the one hand, the easily soluble impurity ions can be discharged from the reaction system with the clear liquid; on the other hand, under the action of gravity, some granular solid impurities will be concentrated at the bottom of the precipitate. During the transportation of the precipitate from the thickener into the reactor, the impurities in the precipitate are removed by filtration and interception, thereby reducing the impurity ion content in the finished product and improving the product purity. In addition, the precipitate treated by the thickener is passed into the reactor again, which can shorten the reaction cycle, increase the yield, and save production costs.

[0012] Furthermore, in step S1, the cobalt salt includes a combination of one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate; and the aluminum salt includes a combination of one or more of aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0013] Furthermore, in step S2, the base liquid is an ammonium bicarbonate solution, and its pH value is 7.3-8.5.

[0014] Furthermore, in step S2, a double-layer stirring device is provided in the reaction container. The double-layer stirring device can stir the material more fully and reduce the occurrence of particle agglomeration.

[0015] Preferably, a double-layer stirring paddle is provided in the reaction vessel, a certain amount of bottom liquid is first added to the reaction kettle, and then bottom water is added until it just touches the second layer of the stirring device.

[0016] Preferably, in step S2, a peristaltic pump is used to control the cobalt salt solution, the ammonium bicarbonate solution and the aluminum salt solution to be fed into the reaction container in parallel.

[0017] Furthermore, in step S2, the flow rate of the ammonium bicarbonate solution is adjusted to control the pH value to be 7.2-7.8 within 30-60 minutes of reaction, and the pH value is reduced to 7.1-7.6 within 2-4 hours of reaction.

[0018] Furthermore, in step S2, the mass ratio of the cobalt salt solution to the ammonium bicarbonate solution is 1:(1.5-2.5), and the mass ratio of the aluminum salt solution to the ammonium bicarbonate solution is 1:(2-6).

[0019] Preferably, the flow rate of the cobalt salt solution is 100-110 L / h, the flow rate of the ammonium bicarbonate solution is 170-180 L / h, and the flow rate of the aluminum salt solution is 70-80 L / h.

[0020] In the present invention, the flow rate of the ammonium bicarbonate solution is controlled to ensure that the pH of the reaction process is within a specified range; the feed flow rates of the cobalt-containing solution and the aluminum-containing solution are controlled to ensure that the aluminum content can reach the target value. Specifically, during the reaction process, the cobalt and aluminum concentrations of the feed solution are sampled and monitored. If the aluminum content is lower than the target value, the feed flow rate of the aluminum salt solution is increased; if the aluminum content is higher than the target value, the feed flow rate of the cobalt salt solution needs to be increased to reduce the aluminum content until the target value is reached.

[0021] Furthermore, in step S3, the specific operation of separating the first cobalt carbonate wet material by using a thickener is as follows: the first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor, and when the liquid level in the reactor is high enough to allow the material to flow into the overflow tank normally, the circulation pump is turned on to allow the material to enter the thickener from the overflow tank; the first cobalt carbonate wet material is separated into a clear liquid and a precipitate in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end of the thickener to continue the reaction.

[0022] During the preparation of wet cobalt carbonate, a small amount of metal impurities such as iron, nickel, and manganese, as well as chloride ions, will be introduced into the reaction system along with the raw materials of cobalt salt and aluminum salt, affecting the purity of the product. Cobalt oxide prepared from this impure wet cobalt carbonate is used in the positive electrode material of the battery. The presence of metal impurities will occupy the effective capacity in the battery, resulting in a low capacity retention rate of the battery, thereby shortening the service life of the battery; in addition, metal impurities will also cause an unbalanced reaction between the positive and negative electrodes of the battery, thereby reducing the cycle life of the battery and accelerating the aging of the battery.

[0023] In the present invention, the concentrator separates the solid particles and liquid in the first cobalt carbonate wet material by gravity sedimentation, and while increasing the solid content, the gravity sedimentation also concentrates the impurity particles at the bottom of the precipitate. A filter is installed on the conveying pipeline from the concentrator to the reactor, and a suitable filter mesh aperture is set to effectively intercept the solid impurity particles entrained in the precipitate, thereby improving the product purity.

[0024] Preferably, the speed of clear liquid discharge from the upper end of the thickener needs to match the feed speed of cobalt salt solution, aluminum salt solution and ammonium bicarbonate solution, and the ratio of the volume of clear liquid discharged per unit time to the feed volume of the three raw materials is controlled at (0.4-0.5): 1, so as to maintain dynamic balance, avoid the occurrence of kettle overflow or the thickener liquid level being too low to cause faults, and improve production efficiency and product quality.

[0025] Furthermore, in step S3, the particle size and metallographic structure are sampled and tested every 3-5 hours, and the growth of the seed crystal is observed until the particle size is controlled at 19.5-19.8 μm and the reaction is terminated.

[0026] Furthermore, in step S3, if the particle size growth rate of the seed crystal is too fast, the tap density will be low, and cracking will easily occur during the subsequent calcination process. If the growth rate is too slow, the reaction time will be prolonged, the consumption of manpower and material resources will increase, and it will be unfavorable for industrial production. In the present invention, the factors of production cost and product performance are comprehensively considered, and the particle size growth rate is controlled by controlling the stirring speed, reaction temperature, reaction pH, and the feed flow rate of the cobalt-containing solution and the aluminum-containing solution, and the growth rate of the seed crystal particle size is controlled at 0.06±0.008μm / h.

[0027] Furthermore, in step S4, the calcination temperature is 250-850° C., and the calcination time is 8-15 hours.

[0028] Preferably, in step S4, calcination is performed in stages at different temperatures. Specifically, the washed and dried cobalt carbonate material is first calcined at a temperature of 250-350° C. for 1-2 hours, then calcined at a temperature of 350-450° C. for 2-3 hours, and finally calcined at a temperature of 750-850° C. for 5-7 hours to obtain aluminum-doped cobalt oxide particles.

[0029] In the above calcination operation, calcination is first carried out under low temperature conditions, and the cobalt carbonate particles release carbon dioxide at a slow rate, which can better maintain the microscopic morphology of the particles; subsequently, as the calcination temperature increases, the cobalt oxide particles show agglomeration growth phenomenon, and the pores inside the particles are filled, so that the sphericity of the cobalt oxide particles is better, and the tap density of the particles can be improved. However, as the calcination temperature is further increased, the specific surface area of ​​the product shows a trend of first increasing and then decreasing. In order to simultaneously take into account the two indicators of tap density and specific surface area, the high temperature section of the calcination of the present invention selects a temperature range of 750-850°C, and finally prepares cobalt oxide with good sphericity and high tap density.

[0030] The technical solution adopted by the present invention to achieve the second purpose is: to provide a carbonate system aluminum-doped cobalt tetroxide, which is prepared by the preparation method according to one of the purposes of the present invention.

[0031] Furthermore, the tap density of the carbonate system aluminum-doped cobalt oxide is 2.46-2.62 g / cm 3 .

[0032] The technical solution adopted by the present invention to achieve the third purpose is: to provide an application of the carbonate system aluminum-doped cobalt tetroxide according to the second purpose of the present invention in lithium ion positive electrode materials.

[0033] The carbonate system aluminum-doped cobalt tetroxide prepared by the present invention has the advantages of high sphericity, high specific surface area and tap density, concentrated particle size distribution, fine primary grains, high tap density, good uniformity of aluminum doping, etc., and its application in lithium ion positive electrode materials can improve the cycle performance, rate performance, working voltage and volume energy density of the positive electrode materials, thereby obtaining a battery with high effective use capacity, strong endurance and long service life.

[0034] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, wherein a cobalt salt solution, an aluminum salt solution and an ammonium bicarbonate solution are introduced into a reaction system in a parallel flow manner, and the amount of aluminum doping is flexibly controlled by adjusting the feed flow rate; in the reaction stage, the pH, reaction temperature and stirring speed of the reaction system are optimized and adjusted to control the crystal seed growth process, and the growth rate of the crystal seed particle size is controlled to 0.06±0.008μm / h, thereby ensuring the quality of the product; in addition, in the present invention, a first cobalt carbonate wet material is treated with a concentrator in the middle stage of the reaction, on the one hand, the clear liquid is discharged, so that the easily soluble ions in the system are discharged, the impurity ion content in the finished product is reduced, and the purity of the product is ensured; on the other hand, the precipitate treated by the concentrator is introduced into the reactor again, which can shorten the reaction cycle, increase the yield, and save production costs.

[0035] (2) The carbonate system aluminum-doped cobalt tetroxide prepared by the present invention has the advantages of high sphericity, high specific surface area and tap density, concentrated particle size distribution, fine primary grains, high tap density, and good uniformity of aluminum doping. At the same time, the raw materials selected from the preparation method of the carbonate system aluminum-doped cobalt tetroxide provided are all common raw materials, which are easy to obtain, and the method is simple to operate and easy to industrialize, and has broad promotion and application prospects in lithium-ion positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope image of aluminum-doped cobalt tetroxide prepared in Example 1 of the present invention; Figure 2 This is a particle size distribution diagram of aluminum-doped cobalt tetroxide prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0039] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0040] The present invention provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: Step 1: prepare a cobalt salt solution with a cobalt ion concentration of 110-140 g / L, an ammonium bicarbonate solution with a concentration of 180-260 g / L, and an aluminum salt solution with an aluminum ion concentration of 2-9 g / L respectively; wherein the cobalt salt includes a combination of one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate; and the aluminum salt includes a combination of one or more of aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0041] Step 2: A double-layer stirring paddle is equipped in the reactor, a certain amount of ammonium bicarbonate solution is added to the reactor as the bottom liquid, and bottom water is added until it just touches the second layer for stirring; the cobalt salt solution, the ammonium bicarbonate solution and the aluminum salt solution are added to the reaction vessel containing the bottom liquid in a parallel flow manner using a peristaltic pump, and the reaction is carried out for 30-40 hours at a temperature of 40-45° C., a pH value of 7.1-7.6 (the pH is reduced to 7.2-7.8 within 30-60 minutes after the reactor is turned on, and the pH is reduced to 7.1-7.6 within 2-4 hours after the reactor is turned on), and a stirring speed of 100-120 r / min to obtain a first cobalt carbonate wet material; during the feeding process, the mass ratio of the cobalt salt solution to the ammonium bicarbonate solution is controlled to be 1:(1.5-2.5), and the mass ratio of the aluminum salt solution to the ammonium bicarbonate solution is controlled to be 1:(2-6).

[0042] Step 3: The first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor. When the liquid level in the reactor is high enough to allow the first cobalt carbonate wet material to flow into the overflow tank normally, the circulation pump is turned on to allow the first cobalt carbonate wet material to enter the thickener from the overflow tank. The clear liquid and the precipitate are separated in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end to continue the reaction. The volume of the clear liquid discharged per unit time and the feed volume of the three raw materials are controlled at (0.4-0.5): 1. The particle size and metallographic phase are measured every 4 hours to observe the growth of the seed crystal. The shutdown particle size is controlled at 19.5-19.8μm, and the particle size growth rate is controlled at about 0.06μm / h to obtain the second cobalt carbonate wet material.

[0043] Step 4: The second cobalt carbonate wet material is washed, dried and calcined, wherein the calcination is carried out in stages at different temperatures: the washed and dried cobalt carbonate material is first calcined at a temperature of 250-300°C for 1-2h, then calcined at a temperature of 350-420°C for 3-4h, and finally calcined at a temperature of 700-850°C for 6-8h to obtain aluminum-doped cobalt oxide particles.

[0044] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0045] Example 1 This embodiment provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: Step 1: preparing a cobalt chloride solution with a cobalt ion concentration of 130 g / L, an ammonium bicarbonate solution with a concentration of 220 g / L, and an aluminum sulfate solution with an aluminum ion concentration of 5 g / L respectively; Step 2: A double-layer stirring paddle is equipped in the reactor, 75 L of 50 g / L ammonium bicarbonate solution is added to the reactor as the base liquid, and 100 L of base water is added until it just touches the second layer for stirring; a peristaltic pump is used to add the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution to the reaction vessel containing the base liquid in a parallel flow manner at flow rates of 100 L / h, 180 L / h and 70 L / h, respectively, during the reaction process, the reaction temperature is controlled to be 45° C., the system pH is 7.2±0.1, the rotation speed is adjusted to 100 r / min, and the reaction is carried out for 30 hours to obtain a first cobalt carbonate wet material; Step 3: The first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor. When the liquid level in the reactor is high enough to allow the first cobalt carbonate wet material to flow into the overflow tank normally, the circulation pump is turned on to allow the first cobalt carbonate wet material to enter the thickener from the overflow tank. The clear liquid and precipitate are separated in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end to continue the reaction. The volume of the clear liquid discharged per unit time and the feed volume of the three raw materials are controlled at 0.45:1. The particle size and metallographic structure are measured every 4 hours to observe the growth of the seed crystal. The shutdown particle size is controlled at 19.5-19.8μm, and the particle size growth rate is controlled at 0.06±0.008μm / h to obtain the second cobalt carbonate wet material.

[0046] Step 4: The second cobalt carbonate wet material is washed, dried and calcined, wherein the drying is carried out by a flash evaporator at a temperature of 120°C for 5 hours; the calcination is carried out in stages at different temperatures: the washed and dried cobalt carbonate material is first calcined at a temperature of 250°C for 2 hours, then calcined at a temperature of 350°C for 3 hours, and finally calcined at a temperature of 850°C for 6 hours, and finally a tap density of 2.53 g / cm is obtained. 3 Aluminum-doped cobalt tetroxide particles.

[0047] The scanning electron microscope image of the aluminum-doped cobalt oxide particles prepared in this example is as follows: Figure 1 The particle size distribution diagram is shown in Figure 2 shown.

[0048] Example 2 This embodiment provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: Step 1: preparing a cobalt chloride solution with a cobalt ion concentration of 110 g / L, an ammonium bicarbonate solution with a concentration of 220 g / L, and an aluminum sulfate solution with an aluminum ion concentration of 6 g / L respectively; Step 2: A double-layer stirring paddle is equipped in the reactor, 75 L of 50 g / L ammonium bicarbonate solution is added to the reactor as the base liquid, and 100 L of base water is added until it just touches the second layer for stirring; a peristaltic pump is used to add the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution to the reaction vessel containing the base liquid in a parallel flow manner at flow rates of 100 L / h, 170 L / h and 80 L / h, respectively. During the reaction process, the reaction temperature is controlled to be 40° C., the system pH is 7.4±0.1, the rotation speed is adjusted to 110 r / min, and the reaction is carried out for 35 hours to obtain a first cobalt carbonate wet material; Step 3: The first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor. When the liquid level in the reactor is high enough to allow the first cobalt carbonate wet material to flow into the overflow tank normally, the circulation pump is turned on to allow the first cobalt carbonate wet material to enter the thickener from the overflow tank. The clear liquid and precipitate are separated in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end to continue the reaction. The volume of the clear liquid discharged per unit time and the feed volume of the three raw materials are controlled at 0.4:1. The particle size and metallographic structure are measured every 4 hours to observe the growth of the seed crystal. The shutdown particle size is controlled at 19.1-19.3μm, and the particle size growth rate is controlled at 0.06±0.008μm / h to obtain the second cobalt carbonate wet material.

[0049] Step 4: The second cobalt carbonate wet material is washed, dried and calcined, wherein the drying is carried out by a flash evaporator at a temperature of 110°C for 5 hours; the calcination is carried out in stages at different temperatures: the washed and dried cobalt carbonate material is first calcined at a temperature of 270°C for 2 hours, then calcined at a temperature of 350°C for 3 hours, and finally calcined at a temperature of 790°C for 7 hours, and finally a tap density of 2.46 g / cm is obtained. 3 Aluminum-doped cobalt tetroxide particles.

[0050] Example 3 This embodiment provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: Step 1: preparing a cobalt chloride solution with a cobalt ion concentration of 130 g / L, an ammonium bicarbonate solution with a concentration of 230 g / L, and an aluminum sulfate solution with an aluminum ion concentration of 5 g / L respectively; Step 2: A double-layer stirring paddle is equipped in the reactor, 75 L of 50 g / L ammonium bicarbonate solution is added to the reactor as the base liquid, and 100 L of base water is added until it just touches the second layer for stirring; a peristaltic pump is used to add the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution to the reaction vessel containing the base liquid in a parallel flow manner at flow rates of 100 L / h, 180 L / h and 70 L / h, respectively. During the reaction process, the reaction temperature is controlled to be 42° C., the system pH is 7.6±0.1, the rotation speed is adjusted to 120 r / min, and the reaction is carried out for 40 hours to obtain a first cobalt carbonate wet material; Step 3: The first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor. When the liquid level in the reactor is high enough to allow the first cobalt carbonate wet material to flow into the overflow tank normally, the circulation pump is turned on to allow the first cobalt carbonate wet material to enter the thickener from the overflow tank. The clear liquid and precipitate are separated in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end to continue the reaction. The volume of the clear liquid discharged per unit time and the feed volume of the three raw materials are controlled at 0.5:1. The particle size and metallographic phase are measured every 4 hours to observe the growth of the seed crystal. The shutdown particle size is controlled at 19.2-19.5μm, and the particle size growth rate is controlled at 0.06±0.008μm / h to obtain the second cobalt carbonate wet material.

[0051] Step 4: The second cobalt carbonate wet material is washed, dried and calcined, wherein the drying is carried out by a flash evaporator at a temperature of 120°C for 5 hours; the calcination is carried out in stages at different temperatures: the washed and dried cobalt carbonate material is first calcined at a temperature of 300°C for 1 hour, then calcined at a temperature of 420°C for 3 hours, and finally calcined at a temperature of 820°C for 6 hours, and finally a tap density of 2.62 g / cm is obtained. 3 Aluminum-doped cobalt tetroxide particles.

[0052] Example 4 This embodiment provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: Step 1: preparing a cobalt chloride solution with a cobalt ion concentration of 120 g / L, an ammonium bicarbonate solution with a concentration of 180 g / L, and an aluminum sulfate solution with an aluminum ion concentration of 2 g / L respectively; Step 2: A double-layer stirring paddle is equipped in the reactor, 75 L of 50 g / L ammonium bicarbonate solution is added to the reactor as the base liquid, and 100 L of base water is added until it just touches the second layer for stirring; a peristaltic pump is used to add the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution to the reaction vessel containing the base liquid in a parallel flow manner at flow rates of 110 L / h, 170 L / h and 80 L / h, respectively. During the reaction process, the reaction temperature is controlled to be 45° C., the system pH is 7.2±0.1, the rotation speed is adjusted to 110 r / min, and the reaction is carried out for 33 hours to obtain a first cobalt carbonate wet material; Step 3: The first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor. When the liquid level in the reactor is high enough to allow the first cobalt carbonate wet material to flow into the overflow tank normally, the circulation pump is turned on to allow the first cobalt carbonate wet material to enter the thickener from the overflow tank. The clear liquid and precipitate are separated in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end to continue the reaction. The volume of the clear liquid discharged per unit time and the feed volume of the three raw materials are controlled at 0.45:1. The particle size and metallographic phase are measured every 4 hours to observe the growth of the seed crystal. The shutdown particle size is controlled at 19.1-19.4μm, and the particle size growth rate is controlled at 0.06±0.008μm / h to obtain the second cobalt carbonate wet material.

[0053] Step 4: The second cobalt carbonate wet material is washed, dried and calcined, wherein the drying is carried out by a flash evaporator at a temperature of 90°C for 7 hours; the calcination is carried out in stages at different temperatures: the washed and dried cobalt carbonate material is first calcined at a temperature of 350°C for 2 hours, then calcined at a temperature of 400°C for 2 hours, and finally calcined at a temperature of 800°C for 5 hours, and finally a tap density of 2.56 g / cm is obtained. 3 Aluminum-doped cobalt tetroxide particles.

[0054] Example 5 This embodiment provides a method for preparing aluminum-doped cobalt tetroxide in a carbonate system, comprising the following steps: Step 1: preparing a cobalt chloride solution with a cobalt ion concentration of 140 g / L, an ammonium bicarbonate solution with a concentration of 260 g / L, and an aluminum sulfate solution with an aluminum ion concentration of 9 g / L respectively; Step 2: A double-layer stirring paddle is equipped in the reactor, 70L of 50g / L ammonium bicarbonate solution is added to the reactor as the base liquid, and 100L of base water is added until it just touches the second layer for stirring; a peristaltic pump is used to add the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution to the reaction vessel containing the base liquid in a parallel flow manner at flow rates of 100L / h, 180L / h and 70L / h, respectively. During the reaction process, the reaction temperature is controlled to be 45°C, the system pH is 7.1±0.1, the rotation speed is adjusted to 120r / min, and the reaction is carried out for 37h to obtain a first cobalt carbonate wet material; Step 3: The first cobalt carbonate wet material in the reactor enters the overflow tank from the top overflow port of the reactor. When the liquid level in the reactor is high enough to allow the first cobalt carbonate wet material to flow into the overflow tank normally, the circulation pump is turned on to allow the first cobalt carbonate wet material to enter the thickener from the overflow tank. The clear liquid and precipitate are separated in the thickener, the clear liquid is discharged from the upper end of the thickener, and the precipitate enters the reactor from the lower end to continue the reaction. The volume of the clear liquid discharged per unit time and the feed volume of the three raw materials are controlled at 0.45:1. The particle size and metallographic structure are measured every 4 hours to observe the growth of the seed crystal. The shutdown particle size is controlled at 19.2-19.5μm, and the particle size growth rate is controlled at 0.06±0.008μm / h to obtain the second cobalt carbonate wet material.

[0055] Step 4: The second cobalt carbonate wet material is washed, dried and calcined, wherein the drying is carried out by a flash evaporator at a temperature of 160°C for 5 hours; the calcination is carried out in stages at different temperatures: the washed and dried cobalt carbonate material is first calcined at a temperature of 300°C for 2 hours, then calcined at a temperature of 450°C for 2 hours, and finally calcined at a temperature of 850°C for 5 hours, and finally a tap density of 2.63 g / cm is obtained. 3 Aluminum-doped cobalt tetroxide particles.

[0056] In summary, the aluminum-doped cobalt tetroxide particles prepared by the method disclosed in the present invention have large particle size, high tap density, and a product particle size D50 that can reach 16-18 μm, and the aluminum element is evenly distributed in the cobalt tetroxide particles, which is conducive to the subsequent preparation of high-voltage batteries.

[0057] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing aluminum-doped cobalt oxide in a carbonate system, characterized in that: The following steps are involved: S1, respectively preparing a cobalt salt solution with a cobalt ion concentration of 110-140 g / L, an ammonium bicarbonate solution with a concentration of 180-260 g / L, and an aluminum salt solution with an aluminum ion concentration of 2-9 g / L; S2, adding the cobalt salt solution, ammonium bicarbonate solution and aluminum salt solution in parallel to the reaction vessel containing the base liquid, reacting for 30-40 hours at a temperature of 40-45° C., a pH value of 7.1-7.6 and a stirring speed of 100-120 r / min to obtain a first cobalt carbonate wet material; S3, the first cobalt carbonate wet material in the reaction container enters a thickener through an overflow tank for separation to obtain a clear liquid and a precipitate; the precipitate enters a reaction container for further reaction to obtain a second cobalt carbonate wet material with a seed particle size of 19.5-19.8 μm; S4. The second cobalt carbonate wet material is washed, dried and calcined to obtain aluminum-doped cobalt tetroxide.

2. The preparation method according to claim 1, characterized in that: In step S1, the cobalt salt includes one or more combinations of cobalt chloride, cobalt sulfate, and cobalt nitrate; the aluminum salt includes one or more combinations of aluminum sulfate, aluminum chloride, and aluminum nitrate.

3. The preparation method according to claim 1, characterized in that: In step S2, the base liquid is an ammonium bicarbonate solution, and its pH value is 7.3-8.

5.

4. The preparation method according to claim 1, characterized in that: In step S2, a double-layer stirring device is provided in the reaction container.

5. The preparation method according to claim 1, characterized in that: In step S2, the flow rate of the ammonium bicarbonate solution is adjusted to control the pH value to be 7.2-7.8 within 30-60 minutes of reaction, and the pH value is reduced to 7.1-7.6 within 2-4 hours of reaction.

6. The preparation method according to claim 5, characterized in that: In step S2, the mass ratio of the cobalt salt solution to the ammonium bicarbonate solution is 1:(1.5-2.5), and the mass ratio of the aluminum salt solution to the ammonium bicarbonate solution is 1:(2-6).

7. The preparation method according to claim 1, characterized in that: In step S3, the growth rate of the seed crystal particle size is controlled at 0.06±0.008 μm / h.

8. The preparation method according to claim 1, characterized in that: In step S4, the calcination temperature is 250-850° C., and the calcination time is 8-15 hours.

9. A carbonate system aluminum-doped cobalt oxide, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the carbonate system aluminum-doped cobalt oxide according to claim 9 in lithium ion positive electrode materials.

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