Cobaltosic oxide, cobalt carbonate and preparation method thereof, and lithium cobalt oxide positive electrode material

Abstract

The invention provides cobaltosic oxide, cobalt carbonate, a preparation method of the cobaltosic oxide and the cobalt carbonate and a lithium cobalt oxide positive electrode material, and relates to the technical field of battery materials. The cobaltosic oxide has a core-shell structure, and an inner core and a shell layer of the cobaltosic oxide have the same element composition; the thickness of the shell layer of the cobaltosic oxide is 0.08 to 0.16 [mu] m; the cobaltosic oxide contains a doping element, and the difference value between the ion radius of the doping element and the radius of Co < 2 + > is 5-10 pm; and the particle size variation D50 of the cobaltosic oxide subjected to 0.75 T pressing is less than 1.8 mu m. The cobaltosic oxide is good in structural stability, the morphology is kept complete after lithium doping, the problem of particle crushing or pulverization caused by volume expansion and shrinkage is avoided, particles are in closer contact during electrode coating, the interface impedance is reduced, and the polarization phenomenon in the charging and discharging process is reduced.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a cobalt tetroxide, cobalt carbonate, their preparation methods, and lithium cobalt oxide cathode materials. Background Technology

[0002] The rapid development of the electronics and communications field has created better opportunities for the lithium-ion battery industry. Lithium cobalt oxide (LCO) materials, due to their high compaction density and high voltage characteristics, have become the mainstream cathode material in the consumer electronics field. To meet the increasing demands of electronic devices for longer battery life, increasing the charging voltage of LCO materials to obtain higher capacity has become a development trend in lithium cobalt oxide materials in recent years. Meanwhile, currently common battery materials are made of large-particle-size spherical cobalt carbonate (D50 greater than 15 micrometers). However, although this size of cobalt carbonate is very easy to synthesize, its overcharge resistance is poor and its cycle performance is low.

[0003] On the other hand, while increasing the charging voltage can effectively improve the capacity of LCO materials, it also reduces the structural stability of the material, especially at voltages above 4.5V, where the cycle life of the material decreases sharply. Doping and surface coating are effective methods to improve the stability of LCO materials at high voltages. Studies have found that by preparing lithium cobalt oxide precursors doped with metal ions with radii similar to those of cobalt ions, and then fabricating LCO cathode materials, their cycle stability at high voltages can be improved. However, unlike aluminum doping, when the radius of the dopant ions is closer to that of cobalt ions, larger primary particles are easily formed after doping, resulting in fewer contact points between particles. Furthermore, with the introduction of these dopant ions, the original crystal structure of the cobalt carbonate precursor may be disrupted, thereby reducing the sintering activity and surface bonding strength of the material. During the sintering of cobalt tetroxide, due to insufficient densification and structural stress imbalance, the particles are prone to powdering, which severely affects the strength of the material and is detrimental to the preparation of lithium cobalt oxide cathode materials.

[0004] Therefore, the key is to improve the problems of powdering and shrinkage of cobalt carbonate particles doped with metal ions with radii similar to cobalt ions during sintering.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a cobalt tetroxide, cobalt carbonate, their preparation methods, and a lithium cobalt oxide cathode material. The cobalt tetroxide is doped with elements whose ionic radii are similar to those of cobalt ions, resulting in small particle size, uniform particle size distribution, good particle morphology consistency, and high strength. Simultaneously, a simple sintering process for doped cobalt tetroxide, which is conducive to industrial production, is provided.

[0007] According to a first aspect of the present invention, a cobalt tetroxide is provided, wherein the cobalt tetroxide has a particle size D50 of 3~4 μm; The cobalt tetroxide has a core-shell structure, and the core and shell of the cobalt tetroxide have the same elemental composition. The shell thickness of the cobalt tetroxide is 0.08~0.16μm; The cobalt tetroxide contains a dopant element, the ionic radius of which is similar to that of Co. 2+ The difference in radius is 5~10 pm; The particle size change ΔD50 of the cobalt tetroxide after being pressed at 0.75T is less than 1.8μm.

[0008] In some embodiments, the cobalt tetroxide has a particle size D90 of 4~6 μm, a span of 0.7±0.22, and a specific surface area of ​​3~4.5 m². 2 / g; And / or, the doping element is at least one of nickel, manganese, lanthanum, magnesium, and titanium.

[0009] In some embodiments, the cobalt tetroxide is doped with nickel and manganese, wherein the nickel doping amount is 0.7%~1.5% and the manganese doping amount is 2%~3%. The doping of nickel and manganese in cobalt tetroxide can effectively suppress the phase transition of the subsequently prepared LCO material above 4.5V, thereby improving the cycling stability of the LCO material at 4.6V. This may be due to the synergistic effect of the three elements: nickel increases specific capacity, manganese enhances structural stability, and cobalt optimizes conductivity.

[0010] According to a second aspect of the present invention, a method for preparing cobalt tetroxide as described in the first aspect is provided, comprising the following steps: Cobalt carbonate is mixed with a pore-forming agent to obtain a premix, and the premix is ​​sintered to obtain cobalt tetroxide. The cobalt carbonate contains a dopant element, and the ionic radius of the dopant element is similar to that of Co. 2+ The difference in radius is 5~10 pm; The grain size of the cobalt carbonate (104) crystal plane is 300~500 Å.

[0011] This invention employs a pore-forming agent during sintering to modify the surface of cobalt carbonate containing doped elements, thereby improving the particle packing density. Simultaneously, due to the radius of the doped element ions and Co... 2+The difference is small; the primary particles of cobalt carbonate raw material are relatively coarse, with fewer gaps between particles and a lower initial porosity. During sintering, the lower porosity may limit the diffusion rate of the material (high diffusion resistance), thus slowing down the densification process of cobalt tetroxide and reducing the degree of shrinkage. This invention utilizes a pore-forming agent to introduce additional pores, increasing the contact points between particles and accelerating the diffusion of ions (such as Ni). 2+ Mn 2+ The diffusion of cobalt tetroxide promotes crystal growth and grain boundary migration, reduces shrinkage resistance, and allows cobalt tetroxide particles to shrink uniformly during sintering, reducing residual voids and microcracks. This ultimately results in a denser cobalt tetroxide structure and improved mechanical stability. The sintered cobalt tetroxide exhibits high strength (with minimal particle size change after 0.75T pressing) and is less prone to powdering. During the lithium doping and mixing stage of lithium cobalt oxide cathode material preparation, no significant powdering or breakage occurs, preventing any impact on the final electrochemical performance of the lithium cobalt oxide cathode material.

[0012] In some embodiments, the pore-forming agent is at least one of ammonium bicarbonate, ammonium carbonate, or ammonium oxalate; and / or, the mass ratio of the pore-forming agent to the cobalt carbonate is (0.01~0.1):1. During sintering, the pore-forming agent decomposes upon heating to generate gases (NH3, CO2, H2O, etc.), forming pores, and leaves no other impurities after decomposition. By increasing porosity, the pore-forming agent assists in shrinkage to prevent gas trapping, reduces the occurrence of closed-cell phenomena, alleviates internal stress concentration in the material, thereby improving the overall uniformity of the material and effectively preventing powder shedding. The nickel-manganese-doped cobalt carbonate particles with high uniformity and concentrated particle size distribution form cobalt tetroxide with small particle size, narrower particle size distribution, high particle size uniformity, low particle size change, and superior particle morphology after sintering. The particle size change is defined as the particle size change ΔD50 after pressing at 0.75T.

[0013] In some embodiments, the mixing is carried out in at least one of a ball mill, a V-type mixer, or a double cone mixer.

[0014] In some preferred embodiments, when the mixing is carried out in a V-type mixer or a double cone mixer, the mixing frequency is 30~50Hz and the mixing time is 5~10min.

[0015] In some embodiments, the sintering is carried out in a sintering furnace, and the sintering process includes: the cobalt carbonate and the pore-forming agent sequentially passing through a low-temperature zone, a transition temperature zone, and a high-temperature zone, with a total sintering time of 15-18 hours; the temperature of the low-temperature zone is 200-300°C, and the sintering time of the cobalt carbonate and the pore-forming agent in the low-temperature zone is 3-4 hours; the temperature of the transition temperature zone is 300-700°C; the temperature of the high-temperature zone is 700-800°C, and the sintering time of the cobalt carbonate and the pore-forming agent in the high-temperature zone is 6-7 hours.

[0016] In some preferred embodiments, the sintering furnace is one of a rotary kiln, a roller kiln, and a suspension furnace.

[0017] In some preferred embodiments, the sintering atmosphere is air; and / or, when the sintering is carried out in a roller kiln, the air inlet flow rate is 3~10L / h.

[0018] According to a third aspect of the present invention, a cobalt carbonate suitable for the preparation method described in the second aspect of the present invention is provided, wherein the cobalt carbonate has a particle size D50 of 3.5~4.0 μm; The cobalt carbonate has a core-shell structure, and the core and shell of the cobalt carbonate have the same elemental composition. The cobalt carbonate contains a dopant element, the ionic radius of which is similar to that of Co. 2+ The difference in radius is 5~10 pm; The shell thickness of the cobalt carbonate is 0.1~0.2μm; The grain size of the cobalt carbonate (104) crystal plane is 300~500 Å.

[0019] In some embodiments, the cobalt carbonate satisfies at least one of the following characteristics: Feature 1: The particle size D90 of the cobalt carbonate is < 8 μm; Feature 2: The tap density of the cobalt carbonate is 2.0 ± 0.5 g / mL; Feature 3: The specific surface area of ​​the cobalt carbonate is 10~35m². 2 / g; Feature 4: The span of the cobalt carbonate is 0.85±0.2; Feature 5: The cobalt carbonate has a spherical morphology.

[0020] Where span = (D90-D10) / D50, D10, D50, and D90 refer to the particle size corresponding to the cumulative particle size distribution based on volume statistics reaching 10%, 50%, and 90%, respectively.

[0021] The physicochemical properties of cobalt carbonate containing doped elements provided by this invention exhibit the following characteristics: primary particles are relatively coarse, with a low specific surface area; the particles are spherical in shape, with small particle size, uniform particle size distribution, and good particle morphology consistency; and there is no powdering or obvious metal segregation on the particle surface. The small-particle-size spherical cobalt carbonate can significantly improve the compaction density of lithium cobalt oxide and greatly improve battery performance.

[0022] According to a fourth aspect of the present invention, a method for preparing cobalt carbonate as described in the third aspect of the present invention is provided, comprising the following steps: S1: Prepare a mixed salt solution containing doped element ions and cobalt ions, a first ammonium bicarbonate solution, and a second ammonium bicarbonate solution; S2: Add the mixed salt solution and the first ammonium bicarbonate solution to the second ammonium bicarbonate solution, and react under heating and stirring conditions. Control the pH within the range of 7.2 to 7.3. When the generated solid particle size D50 reaches 3.05 ± 0.05 μm, adjust the pH to 7.5 to 7.6 until the solid particle size D50 reaches 3.5 to 4 μm, and then stop the reaction.

[0023] In some embodiments, the preparation method satisfies at least one of the following characteristics: Feature 6: The cobalt content in the mixed salt solution is 122~132 g / L; Feature 7: The concentration of the first ammonium bicarbonate solution is 80~100g / L; Feature 8: The concentration of the second ammonium bicarbonate solution is 228~235 g / L; Feature 9: The flow rate ratio of the mixed salt solution to the first ammonium bicarbonate solution is 1:(1.7~2.0), and the flow rate of the first ammonium bicarbonate solution is 12~24 L / h; Feature 10: The heating is performed when the temperature rises to 35~50℃, and the stirring speed is 80~200rpm.

[0024] Appropriately increasing the pH value near the reaction endpoint can form a uniform shell layer on the material surface, avoiding problems such as material segregation caused by doping with other elements. Nickel-manganese-doped cobalt carbonate particles with high uniformity and concentrated particle size distribution can form cobalt tetroxide with small particle size, narrower particle size distribution, high particle size uniformity, high powder strength, and superior particle morphology after sintering.

[0025] In some embodiments, in step S2, the reaction is carried out in a reaction vessel; after the reaction has been carried out for 4 to 7 hours, the reaction liquid in the reaction vessel overflows, and the solid material in the overflowing reaction liquid is collected and added back to the reaction vessel.

[0026] In some embodiments, the cobalt carbonate is further subjected to sequential washing and drying.

[0027] In some preferred embodiments, the washing is carried out in a centrifuge; the washing is performed 3 to 5 times at a ratio of cobalt carbonate to wash water of 1:3; the centrifuge speed is 350 to 400 r / min.

[0028] In some preferred embodiments, the drying is carried out in a flash evaporator, and the moisture content of the dried cobalt carbonate is below 5%.

[0029] According to a fifth aspect of the present invention, a lithium cobalt oxide cathode material is provided, which is obtained by mixing cobalt tetroxide prepared by the method described in the fourth aspect of the present invention or by the preparation method described in the first aspect with a lithium source and then sintering.

[0030] According to a sixth aspect of the present invention, a battery is provided, the battery comprising a positive electrode comprising the lithium cobalt oxide positive electrode material described in the fifth aspect of the present invention.

[0031] According to one embodiment of the present invention, at least the following beneficial effects are achieved: 1. In the X-ray diffraction pattern of cobalt tetroxide containing doped elements provided by this invention, the characteristic peak positions of the doped sample are completely consistent with those of the standard card. After doping (311), the characteristic peak shifts to a smaller angle, indicating that the crystal structure of cobalt tetroxide contains doped elements. This doped cobalt tetroxide structure has good stability, and the morphology remains intact after lithium doping, avoiding particle breakage or pulverization caused by volume expansion and contraction. The particles are in closer contact during electrode coating, reducing interfacial impedance and polarization during charging and discharging. The complete structure also reduces damage to the overall electrode structure, thereby extending the battery cycle life. At the same time, its lattice constant and crystallite size are more uniform, reducing lattice defects and enhancing the thermal stability of the material.

[0032] 2. This invention provides a sintering preparation method for cobalt tetroxide containing doped elements. Compared with conventional sintering processes, this method improves upon the problem of coarse-grained cobalt carbonate particles being difficult to densify after doping. The pore-forming agent enhances the bonding strength between cobalt tetroxide particles by optimizing the pore structure and densification process, reducing the risk of spalling of the sintered body under mechanical stress. The sintered cobalt tetroxide exhibits significant shrinkage, and there are no obvious cracking or powdering phenomena on the particle surface. After lithium doping and mixing, the cobalt tetroxide shows no obvious abnormalities in appearance, while materials sintered using conventional processes show large-area powdering after mixing. Furthermore, this process is simple and conducive to the industrial production of cobalt tetroxide containing doped elements.

[0033] 3. The present invention provides a cobalt carbonate containing doped elements. In its X-ray diffraction pattern, the characteristic peak position of the doped sample is completely consistent with that of the standard card. Among them, the characteristic peak (104) is also shifted to a smaller angle relative to pure cobalt carbonate, indicating that the doping element has been successfully incorporated into the interior of the crystal structure of the cobalt carbonate material. Moreover, the cobalt carbonate particles have small particle size, uniform particle size distribution, good particle morphology consistency, and no obvious metal segregation. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 A simplified process flow diagram of the preparation method of nickel-doped manganese cobalt tetroxide provided in Embodiment 1 of the present invention; Figure 2 SEM image of nickel-manganese-doped cobalt carbonate prepared in Example 1 of this invention. Figure 1 ; Figure 3 SEM image of nickel-manganese-doped cobalt carbonate prepared in Example 1 of this invention. Figure 2 ; Figure 4 This is the EDS image of nickel-manganese-doped cobalt carbonate obtained in Example 1 of the present invention; Figure 5 SEM image of nickel-manganese cobalt tetroxide prepared in Example 1 of this invention. Figure 1 ; Figure 6 SEM image of nickel-manganese cobalt tetroxide prepared in Example 1 of this invention. Figure 2 ; Figure 7 This is a SEM image of a cross-sectional section of nickel-doped cobalt tetroxide obtained in Example 1 of this invention. Figure 8 This is a SEM image of nickel-manganese cobalt tetroxide prepared in Example 1 of the present invention after being mixed with lithium. Figure 9 SEM image of nickel-manganese cobalt tetroxide prepared in Comparative Example 1 of this invention Figure 1 ; Figure 10 SEM image of nickel-manganese cobalt tetroxide prepared in Comparative Example 1 of this invention Figure 2 ; Figure 11 This is a SEM image of the nickel-doped manganese cobalt tetroxide prepared in Comparative Example 1 of this invention after being mixed with lithium. Figure 12 This is a SEM image of the cobalt-free sample prepared in Comparative Example 2 of this invention. Figure 13 This is a SEM image of the undoped cobalt tetroxide obtained in Comparative Example 2 of this invention; Figure 14This is a SEM image of the undoped cobalt tetroxide prepared in Comparative Example 2 of this invention after being mixed with lithium; Figure 15 This is a SEM image of nickel-doped cobalt carbonate obtained in Example 4 of the present invention; Figure 16 This is a SEM image of nickel-doped cobalt tetroxide obtained in Example 4 of the present invention; Figure 17 This is a SEM image of the nickel-doped cobalt tetroxide prepared in Comparative Example 4 of this invention. Figure 18 This is a SEM image of the aluminum-doped cobalt carbonate prepared in Comparative Example 4 of this invention. Figure 19 This is a SEM image of aluminum-doped cobalt tetroxide prepared in Comparative Example 4 of this invention. Figure 20 This is a SEM image of aluminum-doped cobalt tetroxide prepared in Comparative Example 5 of this invention. Figure 21 The XRD patterns of cobalt carbonate prepared in Example 1 and Comparative Example 2 of this invention are shown in comparison. Figure 22 The images show the comparative XRD patterns of cobalt tetroxide prepared in Example 1 and Comparative Example 2 of this invention. Detailed Implementation

[0035] The following detailed description, with appropriate reference to the accompanying drawings, discloses a cobalt carbonate, cobalt tetroxide, and their preparation method, as well as a lithium cobalt oxide cathode material, according to the present invention. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Specifically, "()", ")", "[", and "]" represent intervals, where "()" or ")" represents an open interval, meaning the endpoints of the interval are not included; and "[" and "]" represent a closed interval, meaning the endpoints of the interval are included. A range defined in this way can include endpoints or not, and can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range.

[0037] Specifically, for example, if the ranges 60-120 and 80-110 are listed for a specific parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range “ab” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range “0-5” means that all real numbers between “0-5” have been listed herein, and “0-5” is merely a shortened representation of these numerical combinations. Additionally, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. If (10, 20) is listed, it is understood as any value in the interval 10-20 excluding 10 and 20; (10, 20] is understood as any value in the interval 10-20 excluding 10 but including 20.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0043] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0044] Example 1 This embodiment provides a method for preparing nickel-manganese-doped small-particle cobalt carbonate and cobalt tetroxide, such as... Figure 1 As shown, the nickel doping content in cobalt tetroxide is 0.75%, and the manganese doping content is 2.08%.

[0045] The method for preparing the nickel-manganese-doped small-particle cobalt carbonate is as follows: S1: First, prepare an 800L cobalt chloride solution with a concentration of 125g / L, and add 10kg nickel sulfate and 14kg manganese sulfate solid to it and stir evenly to obtain a mixed metal solution. Next, prepare a 228g / L ammonium bicarbonate solution (precipitant solution) for later use. S2: Add 80 g / L ammonium bicarbonate as a base solution to the reactor. While stirring at 200 rpm, add the mixed metal solution and precipitant solution from S1 to the reactor at a volume ratio of 1:2 (the feed rate of the mixed metal solution is 12 L / h, and the feed rate of the precipitant solution is 24 L / h). Control the temperature of the reaction system at 38℃±0.3℃, and adjust the pH of the reaction system to 7.3 using ammonium bicarbonate solution. When the reactor is continuously fed, it begins to overflow into the overflow tank after 5 hours. At the same time, the overflow tank circulation pump is turned on to continuously pump the material overflowing into the overflow tank back into the reactor. After about 2 hours, the overflow tank begins to overflow, continuously overflowing into the thickener. The thickener pumps away the clear liquid, and the material is returned to the reactor to continue the reaction. When the cobalt carbonate particle size increases to 3.05±0.05μm, the flow rate of the precipitant is controlled to make the pH of the reaction system 7.5-7.6, so that a shell layer of about 0.1μm thick is formed on the surface of the cobalt carbonate. When the particle size D50 of the cobalt carbonate is 3.5-4μm, the feeding is stopped, and the synthesis reaction ends.

[0046] S3: The nickel-manganese co-doped cobalt carbonate slurry obtained in S2 is transferred to a centrifuge for dehydration and washed with hot pure water at 60°C. The solid material and hot pure water are then washed in the centrifuge at a speed of 350 r / min for 7 minutes at a ratio of 1:3. Solid-liquid separation is then performed, and this process is repeated 4 times. The semi-dry cobalt carbonate is then fed into a flash evaporator to dry the moisture content to below 3% to obtain nickel-manganese doped cobalt carbonate.

[0047] The nickel-manganese-doped cobalt carbonate prepared in this embodiment, such as Figure 2 , 3 As shown, the cobalt content is 46.40%, D10 = 2.43 μm, D50 = 3.70 μm, D90 = 5.53 μm, and the particle size exhibits a normal distribution.

[0048] The method for preparing the nickel-manganese-doped small particles of cobalt tetroxide is as follows: S1: First, take 4.2 kg of the nickel-manganese-doped cobalt carbonate raw material prepared above, and mix it with 210 g of ammonium bicarbonate through a double cone mixer. The frequency of the double cone mixer is 40 Hz, and the mixing time is 8 min.

[0049] S2: The uniformly mixed material is then loaded into a sintering sagger and placed in a roller kiln for sintering in an air atmosphere.

[0050] During sintering in the roller kiln, the air inlet flow rate is 8-10 L / h; the temperature in the low-temperature zone is 300 ℃ and the sintering time is 3.5 h; the temperature in the transition temperature zone is 300~750 ℃ ​​and the sintering time is 7 h; the temperature in the high-temperature zone is 750 ℃ ​​and the sintering time is 6.5 h; the total sintering cycle is 17 h.

[0051] S3: After the material cools down, it is sieved and demagnetized to obtain small particles of cobalt tetroxide doped with nickel and manganese.

[0052] Example 2 The difference from Example 1 is that the amount of ammonium bicarbonate used in the pre-sintering treatment stage is twice that of Example 1. The remaining preparation methods and parameters are consistent with those of Example 1.

[0053] Example 3 The difference from Example 1 is that the amount of ammonium bicarbonate used in the pre-sintering treatment stage is 0.2 times that of Example 1. The remaining preparation methods and parameters are consistent with Example 1.

[0054] Example 4 This embodiment provides a method for preparing nickel-doped small-particle cobalt carbonate and cobalt tetroxide, wherein the nickel doping content in the cobalt tetroxide is 0.75%.

[0055] The difference between the above method for preparing nickel-doped small-particle cobalt carbonate and Example 1 is that manganese is not introduced. The remaining preparation methods are consistent with Example 1.

[0056] The preparation method of the nickel-doped small particles of cobalt tetroxide described above is consistent with that in Example 1.

[0057] Comparative Example 1 The difference from Example 1 is that no pretreatment is performed in the preparation of nickel-manganese-doped small-particle cobalt tetroxide; the nickel-manganese-doped cobalt carbonate raw material is directly loaded into a sagger for sintering. The remaining preparation methods and parameters are consistent with those of Example 1.

[0058] Comparative Example 2 The difference from Example 1 is that this comparative example prepares cobalt carbonate particles without any elemental doping, and the preparation method does not introduce nickel or manganese. The remaining preparation methods and parameters are consistent with Example 1.

[0059] The preparation method of cobalt tetroxide without small particles is as follows: S1: First, take 4.2 kg of the cobalt carbonate raw material prepared above without any elemental doping, load it into a sintering sagger, and place it in a roller kiln for sintering. During sintering in the roller kiln, the air inlet flow rate is 8-10 L / h; the temperature in the low-temperature zone is 300 ℃; the temperature in the high-temperature zone is 750 ℃; and the total sintering cycle is 17 h.

[0060] S2: After the material cools down, it is sieved and demagnetized to obtain cobalt tetroxide-free small particles.

[0061] Comparative Example 3 The difference from Example 3 is that no pretreatment is performed in the preparation of nickel-doped small-particle cobalt tetroxide; the nickel-doped cobalt carbonate raw material is directly loaded into a sagger for sintering. The remaining preparation methods and parameters are consistent with those of Example 4.

[0062] Comparative Example 4 This comparative example provides a method for preparing aluminum-doped small-particle cobalt carbonate and cobalt tetroxide, wherein the aluminum doping content in cobalt tetroxide is 0.75%.

[0063] The preparation method of aluminum-doped small-particle cobalt carbonate described above differs from that in Example 1 only in that 10 kg of nickel sulfate and 14 kg of manganese sulfate solids are replaced with 14 kg of aluminum sulfate solids to introduce aluminum. All other preparation methods and parameters remain the same as in Example 1.

[0064] The preparation method of the aluminum-doped small particles of cobalt tetroxide described above is consistent with that in Example 1.

[0065] Comparative Example 5 The difference from Comparative Example 4 is that no pretreatment is performed in the preparation of aluminum-doped small-particle cobalt tetroxide; the aluminum-doped cobalt carbonate raw material is directly loaded into a sagger for sintering. All other preparation methods and parameters remain the same as in Comparative Example 4.

[0066] Experimental Example 1 The morphology and composition of the cobalt tetroxide materials obtained in Examples 1 and 4 and Comparative Examples 1-5 were examined by scanning electron microscopy and XRD, respectively.

[0067] Figure 2-3 , Figure 5-6 SEM images of cobalt carbonate and cobalt tetroxide prepared in Example 1 at different magnifications; Figure 8 This is a SEM image of the lithium-doped mixture from Example 1. Figure 9-10 SEM images of cobalt tetroxide prepared in Comparative Example 1 at different magnifications; Figure 11 The image shows the SEM image of lithium-doped mixture in Comparative Example 1. Figure 12 , Figure 13 SEM images of pure cobalt carbonate and cobalt tetroxide prepared in Comparative Example 2; Figure 14 Here is a SEM image of the lithium-doped mixture from Comparative Example 2; from Figure 2-3 , Figure 5-6 as well as Figure 8 It can be seen that the nickel-manganese cobalt carbonate small particles prepared by the co-precipitation method have relatively coarse primary particles, no segregation on the particle surface, good particle uniformity, and few agglomerated particles; after sintering with pore-forming agent, there are no segregation, cracking, or powdering phenomena in the particle morphology. Figure 4 The image shows the EDS of nickel-manganese-doped cobalt carbonate prepared in Example 1. The EDS data shows no separation or enrichment of any elements on the surface. Figure 7 The image shows a cross-sectional SEM image of the nickel-manganese-doped cobalt tetroxide prepared in Example 1. The cross-sectional slice shows a relatively thin outer shell. After lithium doping, there was no significant powdering in the particle morphology.

[0068] from Figure 9-10 as well as Figure 11 It can be seen that the morphology of directly sintered nickel-manganese cobalt tetroxide particles shows significant depowdering and agglomeration; after lithium mixing, there are more depowdered, broken, and cracked particles, which seriously affect the structural stability of the material. From... Figure 12 , Figure 13 , Figure 14As shown in Table 1, the pure cobalt carbonate particles prepared by the co-precipitation method are relatively smaller than the nickel-manganese-doped particles, exhibit better particle uniformity, and fewer agglomerated particles. After sintering, no agglomeration, cracking, or powdering occurs in the particle morphology, although some particles show over-burning. After lithium doping and mixing, there is also no significant powdering in the particle morphology. Comparative Examples 1 and 2 show that there are significant differences between sintering pure cobalt carbonate and nickel-manganese-doped cobalt carbonate.

[0069] Figure 15 This is a SEM image of the nickel-doped cobalt carbonate prepared in Example 4. Figure 18 The image shows the SEM images of aluminum-doped cobalt carbonate prepared in Comparative Example 4. By comparing the two, it can be found that the primary particles of cobalt carbonate doped with aluminum are finer, while those of cobalt carbonate doped with nickel are coarser. This may be because aluminum doping reduces the nucleation rate of cobalt carbonate, reducing the agglomeration caused by rapid nucleation in the early stage, and thus promoting uniform and fine particle size. Meanwhile, the radius of nickel ions is closer to that of cobalt ions than that of aluminum ions, resulting in less lattice distortion after doping, which is conducive to crystal growth along a specific direction, thereby forming larger particles.

[0070] Figure 16 , 17 SEM images of nickel-doped cobalt tetroxide prepared in Example 4 and Comparative Example 3, respectively; Figure 19 , 20 SEM images of aluminum-doped cobalt tetroxide prepared in Comparative Examples 4 and 5 are shown. The comparison reveals that for cobalt carbonate with fine primary particles and only aluminum doping, no powder loss occurred on the particle surface after sintering, regardless of whether a pore-forming agent was added. However, for cobalt carbonate with only nickel doping, significant powder loss occurred during sintering without a pore-forming agent, while no powder loss occurred after sintering with a pore-forming agent, and the particle surface remained relatively smooth. Figure 21 The XRD patterns of nickel-manganese-doped cobalt carbonate and undoped cobalt carbonate obtained in Example 1 and Comparative Example 2 are shown below. Figure 22 The images show the XRD patterns of nickel-manganese-doped cobalt tetroxide and undoped cobalt tetroxide obtained in Example 1 and Comparative Example 2. Figure 21 It can be seen that the characteristic peak positions of the doped sample are completely consistent with those of the standard card, indicating that Ni and Mn elements have been successfully incorporated. A comparison reveals that after doping with nickel and manganese, the characteristic peak (104) shifts to a smaller angle, indicating that the lattice volume of the cobalt carbonate material has expanded, further demonstrating that Ni and Mn elements have been successfully incorporated into the interior of the material's crystal structure. Figure 22It can also be seen that after nickel-manganese doping, the (311) characteristic peak shifted to a smaller angle. Simultaneously, it was observed that the (311) characteristic peak of nickel-manganese-doped cobalt tetroxide was less sharp than that of pure cobalt. This may be because the periodic arrangement of the original cubic crystal system of cobalt tetroxide was disrupted after nickel-manganese doping, leading to changes in interplanar spacing and a decrease in crystallinity, which in turn easily causes phenomena such as powder shedding during sintering. Therefore, this invention introduces a pore-forming agent to be sintered together with nickel-manganese-doped cobalt carbonate to improve this unfavorable factor. In summary, this invention synthesizes cobalt carbonate and cobalt tetroxide with a core-shell structure by controlling the pH during the reaction process. Under lower pH conditions, the dopant elements are uniformly dispersed and adsorbed within the CoCO3 spheres. Near the reaction endpoint, appropriately increasing the pH value forms a thin layer of crystals that covers the particle surface, thereby suppressing the separation or enrichment of elements on the particle surface during washing. Secondly, the synergistic effect of pre-sintering treatment and a pore-forming agent achieves superior results, improving problems such as primary particle coarsening caused by nickel and manganese doping in cobalt carbonate, difficulty in particle size reduction during sintering, and easy powdering. This has multiple positive impacts on the preparation of downstream lithium cobalt oxide materials. Simultaneously, it effectively suppresses the phase transition of LCO materials above 4.5V, thereby improving the cycling stability of LCO materials at 4.6V.

[0071] Experimental Example 2 The particle size distribution, tap density, specific surface area, and pressure particle size (change in particle size after pressing) of cobalt carbonate and cobalt tetroxide materials obtained in Examples 1-4 and Comparative Examples 1-5 are shown in Tables 1 and 2.

[0072] Among them, the particle size distribution detection method is: LPS wet method test; Tap density testing method: Tap density meter; Specific surface area detection method: nitrogen physical adsorption method; Pressure particle size detection method: dry laser particle size analysis.

[0073] Table 1 Performance parameters of Examples 1-3 and Comparative Examples 1-2

[0074] As shown in Table 1, the nickel-manganese-doped cobalt tetroxide product obtained in Example 1 exhibits high particle size uniformity and significant particle shrinkage. The particle size change after pressing is low, and the particle strength is high. Combined with Examples 2 and 3, it can be seen that appropriately increasing the amount of pore-forming agent can improve the particle shrinkage effect, but after reaching a certain level, even further increases in the amount of pore-forming agent will not significantly improve this effect.

[0075] Compared with Example 1, the nickel-manganese cobalt tetroxide prepared by direct sintering in Comparative Example 1 has poor particle size uniformity, more difficulty in particle size shrinkage, more obvious particle agglomeration, higher particle size change after pressing, and weaker particle strength.

[0076] Compared with Example 1, the tap density of the undoped cobalt carbonate in Comparative Example 2 is relatively low, the primary particles are relatively fine, and the sintering activity is relatively high. Therefore, the required high temperature range is lower than the sintering temperature of nickel-manganese cobalt tetroxide, that is, the sintering activity of cobalt tetroxide will decrease after doping with nickel-manganese.

[0077] Table 2 Performance parameters of Example 4 and Comparative Examples 3-5

[0078] Compared with Comparative Example 3, the nickel-doped cobalt tetroxide product obtained in Example 4 has high particle size uniformity. Although some agglomeration occurred, resulting in larger particle size, the particle size shrinkage was still more obvious than that in Comparative Example 3. The particle size change after pressing was lower, and the particle strength was higher. The nickel-doped cobalt tetroxide prepared by direct sintering in Comparative Example 3 had poor particle size uniformity, more obvious agglomeration, more difficulty in particle size shrinkage, higher particle size change after pressing, and weaker particle strength.

[0079] As can be seen from Comparative Examples 4 and 5, for aluminum-doped cobalt carbonate, there is no significant difference in particle size of the aluminum-doped cobalt tetroxide obtained during sintering, regardless of whether a pore-forming agent is added.

[0080] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. This is applicable to materials whose activity is reduced after doping or coating. Furthermore, without departing from the spirit of this application, various modifications to the embodiments that can be conceived by those skilled in the art, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this application.

Claims

1. A cobalt tetroxide, characterized in that, The particle size D50 of the cobalt tetroxide is 3~4μm; The cobalt tetroxide has a core-shell structure, and the core and shell of the cobalt tetroxide have the same elemental composition. The shell thickness of the cobalt tetroxide is 0.08~0.16μm; The cobalt tetroxide contains a dopant element, the ionic radius of which is similar to that of Co. 2+ The difference in radius is 5~10 pm; The particle size change ΔD50 of the cobalt tetroxide after being pressed at 0.75T is less than 1.8μm.

2. The cobalt tetroxide according to claim 1, characterized in that, The cobalt tetroxide has a particle size D90 of 4~6 μm, a span of 0.7±0.22, and a specific surface area of ​​3~4.5 m². 2 / g; And / or, the doping element is at least one of nickel, manganese, lanthanum, magnesium, and titanium.

3. The cobalt tetroxide according to claim 1, characterized in that, The cobalt tetroxide is doped with nickel and manganese, wherein the nickel doping amount is 0.7%~1.5% and the manganese doping amount is 2%~3%.

4. A method for preparing cobalt tetroxide as described in any one of claims 1-3, characterized in that, Includes the following steps: Cobalt carbonate is mixed with a pore-forming agent to obtain a premix, and the premix is ​​sintered to obtain cobalt tetroxide; The cobalt carbonate contains a dopant element, and the ionic radius of the dopant element is similar to that of Co. 2+ The difference in radius is 5~10 pm; The grain size of the cobalt carbonate (104) crystal plane is 300~500 Å.

5. The preparation method according to claim 4, characterized in that, The pore-forming agent is at least one of ammonium bicarbonate, ammonium carbonate, or ammonium oxalate; and / or, the mass ratio of the pore-forming agent to the cobalt carbonate is (0.01~0.1):

1.

6. A cobalt carbonate, suitable for the preparation method according to claim 4 or 5, characterized in that, The cobalt carbonate has a particle size D50 of 3.5~4.0 μm; The cobalt carbonate has a core-shell structure, and the core and shell of the cobalt carbonate have the same elemental composition. The cobalt carbonate contains a dopant element, the ionic radius of which is similar to that of Co. 2+ The difference in radius is 5~10 pm; The shell thickness of the cobalt carbonate is 0.1~0.2μm; The grain size of the cobalt carbonate (104) crystal plane is 300~500 Å.

7. The cobalt carbonate according to claim 6, characterized in that, The cobalt carbonate satisfies at least one of the following characteristics: Feature 1: The particle size D90 of the cobalt carbonate is < 8 μm; Feature 2: The tap density of the cobalt carbonate is 2.0 ± 0.5 g / ml; Feature 3: The specific surface area of ​​the cobalt carbonate is 10~35m². 2 / g; Feature 4: The span of the cobalt carbonate is 0.85±0.2; Feature 5: The cobalt carbonate has a spherical morphology.

8. A method for preparing cobalt carbonate as described in claim 6 or 7, characterized in that, Includes the following steps: S1: Prepare a mixed salt solution containing doped element ions and cobalt ions, a first ammonium bicarbonate solution, and a second ammonium bicarbonate solution; S2: Add the mixed salt solution and the first ammonium bicarbonate solution to the second ammonium bicarbonate solution, and react under heating and stirring conditions. Control the pH within the range of 7.2 to 7.

3. When the generated solid particle size D50 reaches 3.05 ± 0.05 μm, adjust the pH to 7.5 to 7.6 until the solid particle size D50 reaches 3.5 to 4 μm, and then stop the reaction.

9. The preparation method according to claim 8, characterized in that, The preparation method satisfies at least one of the following characteristics: Feature 6: The cobalt content in the mixed salt solution is 122~132 g / L; Feature 7: The concentration of the first ammonium bicarbonate solution is 80~100g / L; Feature 8: The concentration of the second ammonium bicarbonate solution is 228~235 g / L; Feature 9: The flow rate ratio of the mixed salt solution to the first ammonium bicarbonate solution is 1:(1.7~2.0), and the flow rate of the first ammonium bicarbonate solution is 12~24 L / h; Feature 10: The heating is performed when the temperature rises to 35~50℃, and the stirring speed is 80~200rpm.

10. A lithium cobalt oxide cathode material, characterized in that, Cobalt tetroxide prepared by any one of claims 1-3 or by the preparation method of claim 4 or 5 is mixed with a lithium source and then sintered.

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