Cobalt(ii,iii) oxide and preparation method therefor, lithium cobalt oxide, positive electrode sheet, and battery

Abstract

Disclosed are cobalt(II,III) oxide and a preparation method therefor, lithium cobalt oxide, a positive electrode sheet, and a battery, relating to the technical field of lithium battery positive electrode materials. The cobalt(II,III) oxide has a Dv50, a crystallite size D(111) along the (111) crystal plane, and a specific surface area BET, which satisfy the following relationship: (I), wherein the Dv50 of the cobalt(II,III) oxide is 3 μm-20 μm. The cobalt(II,III) oxide is obtained by pre-sintering and calcining cobalt carbonate having a crystallinity of 30%-80% and a median particle size Dv50 of 3 μm-22 μm.

Description

Cobalt tetroxide and its preparation method, and its applications in lithium cobalt oxide, positive electrode sheets, and batteries.

[0001] Cross-reference to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 2024115875512, filed on November 8, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of lithium battery cathode materials, and more specifically, to a cobalt tetroxide, its preparation method, lithium cobalt oxide, cathode sheet, and battery. Background Technology

[0004] Lithium cobalt oxide cathode materials are widely used in the 3C field due to their advantages of high energy density, good cycle and rate performance. With the hot sales of emerging electronic products such as drones, electric toys, and VR glasses, the market for consumer lithium cobalt oxide has been further boosted.

[0005] Cobalt tetroxide is an important precursor material for the preparation of lithium cobalt oxide. Its physical morphology, structure, grain size, and particle size will be carried over to the lithium cobalt oxide cathode material and have a significant impact on its electrochemical performance. For example, the larger the specific surface area of ​​cobalt tetroxide, the more active sites there are when cobalt tetroxide is sintered with the lithium source, the greater the sintering activity, and the higher the crystallinity of the obtained lithium cobalt oxide, which is beneficial to improving the specific capacity of the cathode material. The specific surface area of ​​cobalt tetroxide is related to several factors, such as particle size, grain size, and porosity of secondary particles. Generally, the smaller the particle size, grain size, and porosity of cobalt tetroxide, the larger the specific surface area. However, excessively small particle size or / and excessively small grain size or / and excessively large porosity will lead to a decrease in the mechanical strength of the particles, resulting in cracking and pulverization during subsequent processing, thus affecting the morphology and performance of lithium cobalt oxide. Therefore, controlling the particle size, grain size, and specific surface area of ​​cobalt tetroxide within an appropriate range is beneficial for obtaining a lithium cobalt oxide precursor that balances good sintering activity and mechanical properties, resulting in lithium cobalt oxide with uniform morphology and good electrochemical performance.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide cobalt tetroxide and its preparation method, as well as lithium cobalt oxide, positive electrode sheet and battery. The aim is to provide cobalt tetroxide with high sintering activity and high mechanical strength, and the lithium cobalt oxide prepared by using it as a precursor has high specific capacity and first charge-discharge efficiency.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides cobalt tetroxide, having the following characteristics: the Dv50, the grain size D(111) of the (111) crystal plane, and the specific surface area BET of cobalt tetroxide satisfy the following relationship: The Dv50 of the cobalt tetroxide is 3μm to 20μm. Dv50 refers to the particle size corresponding to a cumulative particle size distribution of 50% based on volumetric statistics. The unit of BET is meters. 2 / g, the unit of D(111) is μm.

[0010] In some embodiments, the grain size D(111) of the (111) crystal plane of the cobalt tetroxide is 0.0450 μm to 0.0510 μm or 0.0560 μm to 0.0680 μm.

[0011] In some embodiments, the specific surface area (BET) of the cobalt tetroxide is 2 m². 2 / g~6.5m 2 / g.

[0012] In some embodiments, the particle size broadening factor Span of the cobalt tetroxide is less than 1, where Span = (Dv90 - Dv10) / Dv50, and Dv10, Dv50, and Dv90 refer to the particle size corresponding to the cumulative particle size distribution based on volume statistics reaching 10%, 50%, and 90%, respectively; in other embodiments, Span is 0.35 to 0.70.

[0013] In some embodiments, the change rate ΔD% of Dv50 after cobalt tetroxide is pressed at 7500N relative to that before pressing is less than 2.0%; in other embodiments, ΔD% is 0.58% to 1.65%; wherein, ΔD% = (Dv50 - Dv50') / Dv50 × 100%, and Dv50 and Dv50' are the median particle size of the material before and after pressing, respectively.

[0014] In some embodiments, the grain size D(111) of the (111) crystal plane of cobalt tetroxide is 0.0450 μm to 0.0510 μm, and the median grain size Dv50 is 3 μm to 6 μm.

[0015] In some embodiments, the grain size D(111) of the (111) crystal plane of cobalt tetroxide is 0.0560 μm to 0.0680 μm, and the median grain size Dv50 is 16 μm to 20 μm.

[0016] Secondly, the present invention provides a method for preparing cobalt tetroxide, which has the following characteristics: the cobalt tetroxide is obtained by pre-sintering and calcining cobalt carbonate with a crystallinity of 30% to 80% and a median particle size Dv50 of 3 μm to 22 μm.

[0017] In some embodiments, the preparation method of cobalt carbonate is as follows: cobalt salt solution and precipitant solution are added concurrently to a reactor containing a bottom liquid, and stirring is started simultaneously to carry out the reaction. When the material in the reactor reaches the upper limit, the feeding and stirring are stopped, and the mixture is allowed to settle. A portion of the supernatant is extracted, and the above feeding, stirring, settling, and extraction of a portion of the supernatant are repeated until the obtained cobalt carbonate reaches the target particle size. After solid-liquid separation, the solid is taken and washed.

[0018] In some embodiments, the method for preparing cobalt carbonate further includes at least one of the following features:

[0019] Feature 1: The cobalt salt in the cobalt salt solution is at least one of cobalt chloride, cobalt sulfate, and cobalt nitrate, and the concentration of the cobalt salt solution is 2.0 mol / L to 2.5 mol / L;

[0020] Feature 2: The precipitant in the precipitant solution is at least one of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, and potassium carbonate, and the concentration of the precipitant solution is 1.0 mol / L to 3.0 mol / L;

[0021] Feature 3: The cobalt salt solution is added at a flow rate of 20 L / h to 40 L / h, and the precipitant solution is added at a flow rate of 20 L / h to 30 L / h;

[0022] Feature 4: The base liquid is the precipitant solution;

[0023] Feature 5: The stirring speed is 200 rpm to 300 rpm, and the reaction temperature is 40℃ to 55℃;

[0024] Feature 6: The aforementioned extraction of supernatant refers to the extraction of supernatant equivalent to half the capacity of the reactor chamber;

[0025] Feature 7: The target particle size refers to the median particle size Dv50 of cobalt carbonate, which is 3μm to 22μm.

[0026] In some embodiments, the pre-sintering is carried out using a flash dryer; the inlet air temperature of the flash dryer is 300℃~400℃, the outlet air temperature is 150℃~180℃, the main unit speed is 20Hz~30Hz, and the feeding frequency is 10Hz~20Hz.

[0027] In some embodiments, the calcination is carried out in a rotary kiln, the feed frequency of the rotary kiln is 3Hz to 9Hz, the rotation frequency of the furnace tube is 12Hz to 15Hz, the temperature is 710℃ to 760℃, and the calcination time is 3h to 5h.

[0028] Thirdly, the present invention provides a lithium cobalt oxide, which is obtained by mixing cobalt tetroxide obtained from any of the above embodiments with a lithium source and sintering.

[0029] Fourthly, the present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises lithium cobalt oxide as described in the third aspect.

[0030] Fifthly, the present invention also provides a battery, the battery comprising a positive electrode sheet as described in the fourth aspect.

[0031] The present invention has at least the following beneficial effects:

[0032] (1) The cobalt tetroxide provided by the present invention has high reactivity and good mechanical properties with lithium source, and the resulting lithium cobalt oxide has a high lithium ion diffusion rate, thus having a high specific capacity and first charge-discharge efficiency.

[0033] (2) The present invention uses cobalt carbonate with specific crystallinity and particle size to prepare cobalt tetroxide, wherein the cobalt carbonate has both good sintering activity and mechanical strength; by pre-sintering and calcining the cobalt carbonate, the final cobalt tetroxide has good dispersibility and high particle integrity. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0035] Figure 1 is a SEM image of cobalt tetroxide prepared in Example 1;

[0036] Figure 2 is a SEM image of the cobalt tetroxide prepared in Example 6;

[0037] Figure 3 shows the SEM image of cobalt tetroxide prepared in Comparative Example 1;

[0038] Figure 4 shows the SEM image of cobalt tetroxide prepared in Comparative Example 2;

[0039] Figure 5 shows the XRD pattern of cobalt tetroxide prepared in Example 1;

[0040] Figure 6 shows the XRD pattern of cobalt tetroxide prepared in Example 6;

[0041] Figure 7 shows the XRD pattern of cobalt tetroxide prepared in Comparative Example 1;

[0042] Figure 8 shows the XRD pattern of cobalt tetroxide prepared in Comparative Example 2. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0044] This invention provides a cobalt tetroxide, which has the following characteristics: the Dv50, grain size D(111) of the (111) crystal plane, and specific surface area BET of cobalt tetroxide satisfy the following relationship: The Dv50 of the cobalt tetroxide is 3μm to 20μm. Dv50 refers to the particle size corresponding to a cumulative particle size distribution of 50% based on volumetric statistics. The unit of BET is meters. 2 / g, D(111) is in μm, lg(Dv50) represents the logarithm of the Dv50 particle size value, and has no unit.

[0045] The diffraction angles of the (111) cobalt tetroxide crystal plane in the XRD pattern are 2θ = 18° to 20°.

[0046] The grain size D(111) of the cobalt tetroxide (111) crystal plane was obtained by X-ray diffraction (XRD) spectrum analysis. The diffraction angle and full width at half maximum (FWHM) corresponding to the diffraction peaks of the (111) crystal plane were obtained and calculated by Scherrer formula.

[0047] Cobalt tetroxide is an important precursor material for the preparation of lithium cobalt oxide. Its physical morphology, structure, grain size, and particle size will be carried over to the lithium cobalt oxide cathode material and have a significant impact on its electrochemical performance. For example, the larger the specific surface area of ​​cobalt tetroxide, the more active sites there are when cobalt tetroxide is sintered with the lithium source, the greater the sintering activity, and the higher the crystallinity of the obtained lithium cobalt oxide, which is beneficial to improving the specific capacity of the cathode material. The specific surface area of ​​cobalt tetroxide is related to several factors, such as particle size, grain size, and porosity of secondary particles. Generally, the smaller the particle size and grain size of cobalt tetroxide, the greater the porosity and the larger the specific surface area. However, excessively small particle size and / or excessively small grain size and / or excessively large porosity will lead to a decrease in the mechanical strength of the particles, resulting in cracking and pulverization during subsequent processing, thus affecting the morphology and performance of lithium cobalt oxide. Therefore, controlling the particle size, grain size, and specific surface area of ​​cobalt tetroxide within an appropriate range is beneficial for obtaining a lithium cobalt oxide precursor that balances good sintering activity and mechanical properties, resulting in lithium cobalt oxide with uniform morphology and good electrochemical performance.

[0048] The embodiments of the present invention provide a cobalt tetroxide material that meets the above-mentioned value range and has both good sintering activity and mechanical strength, and the resulting lithium cobalt oxide has good lithium-ion diffusion efficiency.

[0049] In some embodiments of the present invention, the grain size D(111) of the (111) crystal plane of the cobalt tetroxide is 0.0450 μm to 0.0510 μm or 0.0560 μm to 0.0680 μm.

[0050] In some embodiments of the present invention, the specific surface area (BET) of the cobalt tetroxide is 2 m². 2 / g~6.5m 2 / g.

[0051] In some embodiments of the present invention, the particle size broadening factor Span of the cobalt tetroxide is less than 1, wherein Span = (Dv90 - Dv10) / Dv50, and Dv10, Dv50, and Dv90 refer to the particle size corresponding to the cumulative particle size distribution based on volume statistics reaching 10%, 50%, and 90%, respectively; in other embodiments of the present invention, Span is 0.35 to 0.70.

[0052] The particle size broadening factor Span reflects the uniformity of cobalt tetroxide particle size. The cobalt tetroxide provided in the embodiments of the present invention has a low Span, indicating that its agglomeration degree is low. The low agglomeration degree is beneficial to improving its mixing and sintering with the lithium source, resulting in a more uniform particle size distribution and higher crystal phase purity of the obtained lithium cobalt oxide, which in turn is beneficial to improving the electrochemical performance of lithium cobalt oxide.

[0053] In some embodiments of the present invention, the change rate ΔD% of Dv50 of the cobalt tetroxide after pressing at 7500N relative to that before pressing is less than 2.0%; in other embodiments of the present invention, ΔD% is 0.58% to 1.65%; wherein, ΔD% = (Dv50 - Dv50') / Dv50 × 100%, and Dv50 and Dv50' are the median particle size of the material particles before and after pressing, respectively.

[0054] The Dv50 change rate ΔD% can be used to evaluate the compressive strength of cobalt tetroxide. Specifically, the higher the compressive strength of cobalt tetroxide, the smaller its ΔD% is, and the less likely it is to cause particle breakage or powdering during subsequent mixing and sintering with lithium source.

[0055] In some embodiments of the present invention, the grain size D(111) of the (111) crystal plane of cobalt tetroxide is 0.0450 μm to 0.0510 μm, and the median grain size Dv50 is 3 μm to 6 μm.

[0056] In some embodiments of the present invention, the grain size D(111) of the (111) crystal plane of cobalt tetroxide is 0.0560 μm to 0.0680 μm, and the median grain size Dv50 is 12 μm to 20 μm.

[0057] Secondly, embodiments of the present invention provide a method for preparing cobalt tetroxide, which has the following characteristics:

[0058] Cobalt tetroxide is obtained by pre-sintering and calcining cobalt carbonate with a crystallinity of 30% to 80% and a median particle size Dv50 of 3 μm to 22 μm.

[0059] This invention prepares cobalt tetroxide using cobalt carbonate with specific crystallinity and particle size. This results in cobalt carbonate possessing high sintering activity and good mechanical strength, preventing surface powdering and damage during flash drying and deagglomeration. Furthermore, cobalt carbonate with specific crystallinity and particle size can be obtained by pre-sintering and calcination to meet the required specifications. Cobalt tetroxide.

[0060] In some embodiments of the present invention, cobalt carbonate with a crystallinity of 50% to 80% and a median particle size Dv50 of 3 μm to 7 μm is pre-sintered and calcined to obtain cobalt tetroxide with a (111) crystal plane grain size D(111) of 0.0450 μm to 0.0510 μm and a median particle size Dv50 of 3 μm to 6 μm.

[0061] In some embodiments of the present invention, cobalt carbonate with a crystallinity of 30% to 65% and a median particle size Dv50 of 13 μm to 22 μm is pre-sintered and calcined to obtain cobalt tetroxide with a (111) crystal plane grain size D(111) of 0.0560 μm to 0.0680 μm and a median particle size Dv50 of 12 μm to 20 μm.

[0062] In some embodiments of the present invention, the method for preparing cobalt carbonate is as follows: cobalt salt solution and precipitant solution are added concurrently to a reactor containing a bottom liquid, and stirring is started simultaneously to react until the material in the reactor reaches the upper limit. Then, the feeding and stirring are stopped, and the mixture is allowed to settle. A portion of the supernatant is removed, and the above feeding, stirring, settling, and removal of a portion of the supernatant are repeated until the cobalt carbonate obtained reaches the target particle size. After solid-liquid separation, the solid is taken and washed.

[0063] In some embodiments of the present invention, the method for preparing cobalt carbonate further includes at least one of the following features:

[0064] Feature 1: The cobalt salt in the cobalt salt solution is at least one of cobalt chloride, cobalt sulfate, and cobalt nitrate, and the concentration of the cobalt salt solution is 2.0 mol / L to 2.5 mol / L;

[0065] Feature 2: The precipitant in the precipitant solution is at least one of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, and potassium carbonate, and the concentration of the precipitant solution is 1.0 mol / L to 3.0 mol / L;

[0066] Feature 3: The cobalt salt solution is added at a flow rate of 20 L / h to 40 L / h, and the precipitant solution is added at a flow rate of 20 L / h to 30 L / h;

[0067] Feature 4: The base liquid is the precipitant solution;

[0068] Feature 5: The stirring speed is 200 rpm to 300 rpm, and the reaction temperature is 40℃ to 55℃;

[0069] Feature 6: The aforementioned extraction of supernatant refers to the extraction of supernatant equivalent to half the capacity of the reactor chamber;

[0070] Feature 7: The target particle size refers to the median particle size Dv50 of cobalt carbonate, which is 3μm to 22μm.

[0071] By adjusting the preparation process of cobalt carbonate, this invention can obtain cobalt carbonate with specific crystallinity and particle size.

[0072] In some embodiments of the present invention, the pre-sintering is carried out using a flash dryer; the inlet air temperature of the flash dryer is set to 300℃~400℃, the outlet air temperature is set to 150℃~180℃, the main unit speed is set to 20Hz~30Hz, and the feeding frequency is set to 10Hz~20Hz.

[0073] In this embodiment of the invention, the washed cobalt carbonate is fed into a flash dryer for drying and pre-sintering. The particles shrink instantaneously under high heat, reducing the interface between agglomerated particles. At the same time, the stirring blades of the flash dryer further disrupt the interface between agglomerated particles, achieving the purpose of deagglomeration, allowing the particles to disperse individually, and improving particle consistency.

[0074] In some embodiments of the present invention, the calcination is carried out in a rotary kiln, with a feeding frequency of 3Hz to 9Hz, a furnace tube rotation frequency of 12Hz to 15Hz, a calcination time of 3h to 5h, and a calcination temperature of 710℃ to 760℃.

[0075] In this embodiment of the invention, the grain size corresponding to the (111) crystal plane of cobalt tetroxide is controlled within a suitable range by controlling the calcination temperature and calcination time.

[0076] Thirdly, embodiments of the present invention provide a lithium cobalt oxide, which is obtained by mixing cobalt tetroxide obtained in any of the above embodiments with a lithium source and sintering.

[0077] In an optional embodiment, the lithium source includes at least one of lithium carbonate and lithium hydroxide.

[0078] Fourthly, embodiments of the present invention provide a positive electrode sheet, wherein the positive electrode sheet comprises lithium cobalt oxide as described in the third aspect.

[0079] Fifthly, the battery is prepared using the positive electrode sheet described in the fourth aspect.

[0080] This invention also provides a lithium battery, including the above-mentioned positive electrode, and may further include a negative electrode, electrolyte, separator, etc., to form a complete battery structure.

[0081] The features and performance of this document are further described in detail below with reference to embodiments.

[0082] The test in this article is as follows:

[0083] (1) X-ray diffraction (XRD): In this paper, an energy scattering X-ray diffractometer was used to perform XRD tests on the prepared cobalt carbonate and cobalt tetroxide. Kα rays of Cu were used for the tests, with a wavelength λ of [wavelength missing]. The scanning angle was 10°–68°, and the scanning speed was 3° / min. XRD test results were analyzed using Jade 6 software, including full-spectrum fitting and R-squared refinement. wp ≤9% (R) wp (This is a weighted residual variance factor to ensure the precision of the refinement). Diffraction peaks with a full width at half maximum (FWHM) greater than 3° are amorphous peaks, and diffraction peaks with a FWHM less than 3° are crystalline peaks. The crystallinity of cobalt carbonate is calculated as follows: the sum of the peak areas of all crystalline peaks / the total area of ​​all peaks * 100%. The grain size corresponding to the cobalt tetroxide (111) crystal plane is calculated as follows: based on the diffraction angle (θ) and the FWHM (β) of the diffraction peaks of the (111) crystal plane and calculated according to the Scherrer formula, the Scherrer formula is: k is a constant value, taking the value 0.9; λ refers to the wavelength of the incident light. When using this formula to calculate the grain size, the full width at half maximum (FWHM) of the diffraction peak (β) is converted to radians for calculation.

[0084] (2) Particle size and distribution: The particle size and distribution of the prepared cobalt carbonate and cobalt tetroxide were tested using a Malvern 3000 laser particle size analyzer.

[0085] (3) Scanning electron microscopy (SEM): Field emission scanning electron microscopy was used to observe and analyze the surface morphology of cobalt tetroxide.

[0086] (4) Particle size Dv50 change rate (ΔD%): The powder compaction density meter was used to test the compressive strength of the material particles by the particle size Dv50 change rate (ΔD%). ΔD% = (Dv50-Dv50') / Dv50×100%, where Dv50 and Dv50' are the median particle size of the material before and after compaction, respectively, and the compaction pressure is 7500N.

[0087] (5) Charge and discharge test: The coin cell was assembled with lithium cobalt oxide as the positive electrode material and the charge and discharge test was carried out. The test temperature was 25℃, the voltage range was 3.0V~4.50V, and the rate was 0.1C. Specifically, the assembly of the coin cell included the following steps: ① Preparation of lithium cobalt oxide: Cobalt tetroxide and lithium carbonate were mixed with n(Co):n(Li) at a ratio of 1:1.05, ground, dried, calcined at 1050℃ for 30h, crushed, and sieved to obtain lithium cobalt oxide; ② Preparation of positive electrode sheet: Lithium cobalt oxide:acetylene black:PVDF were mixed into a uniform slurry at a mass ratio of 75:15:10, uniformly coated on an aluminum foil substrate and dried; ③ Battery assembly: The electrolyte was a 1mol / L LiPF6 solution, and the solvent was a mixed solvent of EC and DMC with a volume ratio of 1:1; the negative electrode was graphite; the positive electrode, negative electrode, electrolyte, and separator were assembled into a battery in an argon-protected glove box.

[0088] The XRD patterns of cobalt tetroxide prepared in Examples 1, 6, and Comparative Examples 1 and 2 of this invention are shown in Figures 5 to 8 of the specification. As can be seen from the figures, cobalt tetroxide was successfully prepared in the examples of this invention. The grain size of the (111) crystal plane can be calculated from the diffraction angle and full width at half maximum (FWHM) of the crystal plane in the XRD pattern.

[0089] Example 1

[0090] A method for preparing cobalt tetroxide includes the following steps:

[0091] (1) 100 L of 1.5 mol / L sodium carbonate solution was added to the reactor as the base liquid. 2.0 mol / L cobalt chloride solution was added to the reactor at a rate of 20 L / h and 1.5 mol / L sodium carbonate solution at a rate of 30 L / h, in parallel flow. At the same time, the stirring speed was turned on and adjusted to 300 rpm, and the temperature was adjusted to 40℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt chloride solution and sodium carbonate solution were added in parallel flow, and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 8 times to obtain cobalt carbonate with a median particle size Dv50 of 4.0 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 54.62%.

[0092] (2) The filter cake obtained in step (1) is put into a flash dryer for drying and sintering to obtain pre-sintered cobalt carbonate; the inlet air temperature of the flash dryer is set to 300℃, the outlet air temperature is set to 150℃, the main unit speed is set to 20Hz, and the feeding frequency is set to 10Hz.

[0093] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 3Hz, the furnace tube rotation frequency is set to 12Hz, the material residence time in the furnace tube is 3h, and the calcination temperature is 710℃.

[0094] Figure 1 in the instruction manual shows the cobalt tetroxide prepared in Example 1. As can be seen from the figure, the cobalt tetroxide particles have good dispersibility, uniform primary particle size, and narrow particle size distribution.

[0095] Example 2

[0096] A method for preparing cobalt tetroxide includes the following steps:

[0097] (1) 200 L of 2.0 mol / L ammonium bicarbonate solution was added to the reactor as the base liquid. Cobalt sulfate solution with a concentration of 2.5 mol / L was added to the reactor in parallel at a rate of 25 L / h and ammonium bicarbonate solution with a concentration of 2.0 mol / L at a rate of 30 L / h. At the same time, the stirring speed was turned on and adjusted to 200 rpm, and the temperature was adjusted to 48℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to stand until the material settled completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt sulfate solution and ammonium bicarbonate solution were added in parallel and the stirring was turned on for reaction. The above standing, removal of part of the supernatant and feeding operation was repeated 12 times to obtain cobalt carbonate with a median particle size Dv50 of 6.2 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 64.85%.

[0098] (2) The filter cake obtained in step (1) is put into a flash dryer for drying and sintering to obtain pre-sintered cobalt carbonate; the inlet air temperature of the flash dryer is set to 400℃, the outlet air temperature is set to 180℃, the main unit speed is set to 30Hz, and the feeding frequency is set to 20Hz.

[0099] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 9Hz, the furnace tube rotation frequency is set to 15Hz, the material residence time in the furnace tube is 5h, and the calcination temperature is 730℃.

[0100] Example 3

[0101] (1) 120 L of 3 mol / L potassium carbonate solution was added to the reactor as the base liquid. 2.2 mol / L cobalt sulfate solution was added to the reactor at a rate of 40 L / h and 20 L / h of 3 mol / L potassium carbonate solution, respectively. At the same time, the stirring speed was turned on and adjusted to 260 rpm, and the temperature was adjusted to 55℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. Half of the supernatant in the reactor cavity was removed. Then, the cobalt sulfate solution and potassium carbonate solution were added in parallel and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 13 times to obtain cobalt carbonate with a median particle size Dv50 of 6.9 μm. The cobalt carbonate was filtered by centrifuge and washed three times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 76.63%.

[0102] (2) The filter cake obtained in step (1) is put into a flash dryer for drying and sintering to obtain pre-sintered cobalt carbonate; the inlet air temperature of the flash dryer is set to 380℃, the outlet air temperature is set to 170℃, the main unit speed is set to 26Hz, and the feeding frequency is set to 12Hz.

[0103] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 5Hz, the furnace tube rotation frequency is set to 12Hz, the material residence time in the furnace tube is 3.5h, and the calcination temperature is 720℃.

[0104] Example 4

[0105] (1) 160 L of 2.6 mol / L sodium bicarbonate solution was added to the reactor as the base liquid. 2.3 mol / L cobalt nitrate solution was added to the reactor in parallel at a rate of 30 L / h and 2.6 mol / L sodium bicarbonate solution at a rate of 28 L / h. At the same time, the stirring speed was turned on and adjusted to 220 rpm, and the temperature was adjusted to 43℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt nitrate solution and sodium bicarbonate solution were added in parallel and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 9 times to obtain cobalt carbonate with a median particle size Dv50 of 4.2 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 58.71%.

[0106] Steps (2) to (3) are the same as in Example 1.

[0107] Example 5

[0108] The difference from Example 1 is that in step (3), the feeding frequency is set to 9Hz, the furnace tube rotation frequency is set to 15Hz, the material residence time in the furnace tube is 5h, and the calcination temperature is 730℃.

[0109] Example 6

[0110] (1) 100 L of 1.5 mol / L sodium carbonate solution was added to the reactor as the base liquid. 2.0 mol / L cobalt chloride solution was added to the reactor at a rate of 20 L / h and 1.5 mol / L sodium carbonate solution at a rate of 30 L / h, in parallel flow. At the same time, the stirring speed was turned on and adjusted to 200 rpm, and the temperature was adjusted to 40℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt chloride solution and sodium carbonate solution were added in parallel flow, and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 20 times to obtain cobalt carbonate with a median particle size Dv50 of 18.8 μm. The cobalt carbonate was filtered by centrifuge and washed three times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 30%.

[0111] (2) The filter cake obtained in step (1) is put into a flash dryer for drying and sintering to obtain pre-sintered cobalt carbonate; the inlet air temperature of the flash dryer is set to 360℃, the outlet air temperature is set to 150℃, the main unit speed is set to 22Hz, and the feeding frequency is set to 13Hz.

[0112] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 3Hz, the furnace tube rotation frequency is set to 12Hz, the material residence time in the furnace tube is 3h, and the calcination temperature is 740℃.

[0113] Figure 2 in the instruction manual shows the cobalt tetroxide prepared in Example 6. As can be seen from the figure, the cobalt tetroxide particles have good dispersibility, uniform primary particle size, and narrow particle size distribution.

[0114] Example 7

[0115] (1) 100 L of 1.5 mol / L sodium carbonate solution was added to the reactor as the base liquid. 2.0 mol / L cobalt chloride solution was added to the reactor at a rate of 20 L / h and 1.5 mol / L sodium carbonate solution at a rate of 30 L / h, in parallel flow. At the same time, the stirring speed was turned on and adjusted to 200 rpm, and the temperature was adjusted to 45℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt chloride solution and sodium carbonate solution were added in parallel flow, and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 22 times to obtain cobalt carbonate with a median particle size Dv50 of 21.0 μm. The cobalt carbonate was filtered by centrifuge and washed three times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 45%.

[0116] Step (2) is the same as in Example 6.

[0117] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 3Hz, the furnace tube rotation frequency is set to 12Hz, the material residence time in the furnace tube is 3h, and the calcination temperature is 750℃.

[0118] Example 8

[0119] (1) 100 L of 1.5 mol / L sodium carbonate solution was added to the reactor as the base liquid. 2.0 mol / L cobalt chloride solution was added to the reactor at a rate of 20 L / h and 1.5 mol / L sodium carbonate solution at a rate of 30 L / h, in parallel flow. At the same time, the stirring speed was turned on and adjusted to 200 rpm, and the temperature was adjusted to 55℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt chloride solution and sodium carbonate solution were added in parallel flow, and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 24 times to obtain cobalt carbonate with a median particle size Dv50 of 22.0 μm. The cobalt carbonate was filtered by centrifuge and washed three times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 60%.

[0120] Step (2) is the same as in Example 6.

[0121] (2) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 3Hz, the furnace tube rotation frequency is set to 12Hz, the material residence time in the furnace tube is 3h, and the calcination temperature is 760℃.

[0122] Comparative Example 1

[0123] The difference from Example 1 is that in step (2), the inlet air temperature of the flash dryer is set to 150°C, the outlet air temperature is set to 90°C, the main unit speed is set to 20Hz, and the feeding frequency is set to 10Hz.

[0124] Figure 3 in the instruction manual shows the cobalt tetroxide prepared in Comparative Example 1. As can be seen from the figure, large agglomerates appear in the sample, and the surface morphology of the agglomerates is different from that of the dispersed particles, indicating that the particles have undergone over-burning and fusion. The reason is that the fluidity of the agglomerated particles in the furnace tube becomes poor and the heating is uneven.

[0125] Comparative Example 2

[0126] The difference from Example 1 is that the reaction temperature in step (1) is 60°C, and the cobalt carbonate obtained has a median particle size Dv50 of 4.0 μm. The crystallinity of the cobalt carbonate sample was 87.48% as determined by XRD.

[0127] Figure 4 in the instruction manual shows the cobalt tetroxide prepared in Comparative Example 2. It can be seen from the figure that there is powder shedding on the surface of the sample particles. The reason is that the grain size of the (111) crystal plane is too small, the particle bonding force is poor, and the surface structure stability of the material is poor.

[0128] Comparative Example 3

[0129] (1) 170 L of 2.4 mol / L sodium bicarbonate solution was added to the reactor as the base liquid. 2.3 mol / L cobalt nitrate solution was added to the reactor in parallel at a rate of 29 L / h and 2.4 mol / L sodium bicarbonate solution at a rate of 26 L / h. At the same time, the stirring speed was turned on and adjusted to 220 rpm, and the temperature was adjusted to 35℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt nitrate solution and sodium bicarbonate solution were added in parallel and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 10 times to obtain cobalt carbonate with an average particle size of 4.2 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 43.61%.

[0130] Steps (2) to (3) are the same as in Example 1.

[0131] Comparative Example 4

[0132] The difference from Example 6 is that the reaction temperature in step (1) is 60°C, and the crystallinity of the cobalt carbonate sample is 90.7% as determined by XRD.

[0133] Comparative Example 5

[0134] The difference from Example 6 is that the reaction temperature in step (1) is 33°C, and the crystallinity of the cobalt carbonate sample is 25.6% as determined by XRD.

[0135] The physical parameters and properties of cobalt tetroxide prepared in the embodiments and comparative examples of the present invention are shown in Tables 1 and 2.

[0136] Table 1

[0137] Table 2

[0138] The data in the table show that the cobalt tetroxide prepared in the comparative example does not meet the requirements. The specific capacity of the lithium cobalt oxide prepared by these methods was worse than that of the examples, indicating that maintaining the numerical relationships of BET, Dv50, and D(111) of cobalt tetroxide at a reasonable level is beneficial for obtaining cobalt tetroxide with high mechanical and electrochemical performance. Specifically, Comparative Examples 1, 3, and 5... Less than 3.33g -1 Although the obtained cobalt tetroxide has a low ΔD% (i.e. better mechanical properties), it is easy to cause uneven particle size distribution of the product. Therefore, the broadening coefficients of comparative examples 1, 3, and 5 are large. Furthermore, due to the small BET, the lithium diffusion efficiency of the lithium cobalt oxide prepared by it decreases, thereby reducing the specific capacity.

[0139] Comparative Examples 2 and 4 More than 6.90g -1 Therefore, its ΔD% is much larger than that of the example. Due to its poor mechanical properties, the material is easily broken and pulverized during the subsequent preparation of lithium cobalt oxide, resulting in an excessively wide particle size distribution of the obtained lithium cobalt oxide, which in turn reduces its specific capacity.

[0140] In Example 2, [Dv50×D(111)] = 0.1978 μm 2 The [Dv50×D(111)] of Comparative Example 1 is 0.1935μm. 2 However, because the material particles in Example 2 have better dispersion, they have a higher BET, and therefore meet the requirements. By balancing good mechanical strength and sintering activity, the resulting cathode material has a large specific capacity, indicating that the numerical relationship between BET, Dv50 and D(111) is maintained at a reasonable level, which is conducive to obtaining cobalt tetroxide with high mechanical strength and good sintering activity.

[0141] Comparison of Examples 1 and 4 with Comparative Examples 2 and 3 shows that by adjusting the process parameters for preparing cobalt carbonate, cobalt carbonate with different crystallinities can be obtained. Analysis of the data in Table 1 shows that cobalt carbonate with different crystallinities has a significant impact on the grain size of the (111) crystal plane of the final product, cobalt tetroxide. Specifically, the higher the crystallinity of cobalt carbonate, the smaller the grain size of the (111) crystal plane of cobalt tetroxide. This is because when cobalt carbonate has a high crystallinity, it has a more regular crystal structure, the interfacial energy is reduced, and it is conducive to the formation of fine cobalt tetroxide grains during sintering, thereby reducing the grain size of the (111) crystal plane.

[0142] A comparison of Examples 1 and 5 shows that the calcination process conditions affect the grain size of the (111) crystal plane of cobalt tetroxide. This is because the higher the calcination temperature and the longer the time, the more sufficient the time and energy for grain growth and development, resulting in a larger grain size, and vice versa.

[0143] A comparison of Example 1 and Comparative Example 1 shows that the flash drying process conditions affect the particle size, agglomeration degree, and grain size of the (111) crystal plane of cobalt tetroxide. This is because when the flash temperature is low, only the drying effect is achieved, and the agglomeration and particle size of cobalt carbonate do not change. When the flash temperature is high, cobalt carbonate undergoes an oxidative decomposition reaction in addition to drying and dehydration. Furthermore, since Comparative Example 1 has an agglomerated structure and its (111) crystal plane grain size is higher than that of Example 1, its specific capacity is lower.

[0144] Example 9

[0145] (1) 138 L of 2.4 mol / L ammonium bicarbonate solution was added to the reactor as the base liquid. 2.0 mol / L cobalt nitrate solution was added to the reactor in parallel at a rate of 20 L / h and 2.4 mol / L ammonium bicarbonate solution at a rate of 25 L / h. At the same time, the stirring speed was turned on and adjusted to 276 rpm, and the temperature was adjusted to 41℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt nitrate solution and ammonium bicarbonate solution were added in parallel and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 10 times to obtain cobalt carbonate with a median particle size Dv50 of 7.8 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 57.1%.

[0146] Steps (2) to (3) are the same as in Example 3.

[0147] Example 10

[0148] (1) 124 L of 2.5 mol / L sodium bicarbonate solution was added to the reactor as the base liquid. 2.2 mol / L cobalt nitrate solution was added to the reactor in parallel at a rate of 35 L / h and 2.5 mol / L sodium bicarbonate solution at a rate of 29 L / h. At the same time, the stirring speed was turned on and adjusted to 220 rpm, and the temperature was adjusted to 46℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to settle completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt nitrate solution and sodium bicarbonate solution were added in parallel and the stirring was turned on for reaction. The above settling, removal of part of the supernatant, and feeding operations were repeated 14 times to obtain cobalt carbonate with a median particle size Dv50 of 13.9 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain a filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 52.3%.

[0149] Step (2) is the same as in Example 6.

[0150] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 6Hz, the furnace tube rotation frequency is set to 14Hz, the material residence time in the furnace tube is 3h, and the calcination temperature is 740℃.

[0151] Example 11

[0152] (1) 136 L of 1.2 mol / L ammonium bicarbonate solution was added to the reactor as the base liquid. Cobalt chloride solution with a concentration of 2.0 mol / L was added to the reactor in parallel at a rate of 25 L / h and ammonium bicarbonate solution with a concentration of 1.2 mol / L at a rate of 23 L / h. At the same time, the stirring speed was turned on and adjusted to 240 rpm, and the temperature was adjusted to 51℃ for reaction. When the material in the reactor reached the upper limit, the feeding and stirring were stopped, and the mixture was allowed to stand until the material settled completely. The supernatant equivalent to half the capacity of the reactor cavity was removed. Then, the cobalt chloride solution and sodium carbonate solution were added in parallel and the stirring was turned on for reaction. The above standing, removal of part of the supernatant and feeding operation was repeated 21 times to obtain cobalt carbonate with a median particle size Dv50 of 21.9 μm. The cobalt carbonate was filtered by centrifuge and washed 3 times with pure water to obtain filter cake. The crystallinity of the cobalt carbonate sample was tested by XRD and found to be 65%.

[0153] Step (2) is the same as in Example 6.

[0154] (3) The pre-sintered cobalt carbonate obtained in step (2) is fed into a rotary kiln for calcination to obtain cobalt tetroxide; the feeding frequency is set to 4Hz, the furnace tube rotation frequency is set to 15Hz, the material residence time in the furnace tube is 4.5h, and the calcination temperature is 755℃.

[0155] The physical parameters of the cobalt tetroxide prepared in Examples 9-11 are shown in Table 3.

[0156] Table 3

[0157] As shown in Table 3, the preparation method provided in this embodiment of the invention can produce Dv50 with a diameter of 3μm to 20μm, and meets the requirements. Cobalt tetroxide has a low particle size distribution coefficient and good mechanical properties.

Claims

1. A cobalt tetroxide, characterized in that, The Dv50, grain size D(111), and specific surface area BET of the cobalt tetroxide satisfy the following relationship: The Dv50 of the cobalt tetroxide is 3 μm to 20 μm. Dv50 refers to the particle size corresponding to a cumulative particle size distribution of 50% based on volumetric statistics. The unit of BET is meters. 2 / g, the unit of D(111) is μm.

2. The cobalt tetroxide according to claim 1, characterized in that, The grain size D(111) of the (111) crystal plane of the cobalt tetroxide is 0.0450μm~0.0510μm or 0.0560μm~0.0680μm; Or / and, the specific surface area (BET) of the cobalt tetroxide is 2 m². 2 / g~6.5m 2 / g; Or / and, the particle size broadening coefficient Span of the cobalt tetroxide is less than 1, where Span = (Dv90 - Dv10) / Dv50, and Dv10, Dv50, and Dv90 refer to the particle size corresponding to the cumulative particle size distribution based on volume statistics reaching 10%, 50%, and 90%, respectively. Or / and, the change rate ΔD% of the cobalt tetroxide Dv50 after pressing at 7500N relative to the unpressed state is less than 2.0%.

3. The cobalt tetroxide according to claim 1 or 2, characterized in that, The grain size D(111) of the (111) crystal plane of the cobalt tetroxide is 0.0450μm to 0.0510μm, and the median grain size Dv50 is 3μm to 6μm.

4. The method for preparing cobalt tetroxide according to any one of claims 1 to 3, characterized in that, The cobalt tetroxide is obtained by pre-sintering and calcining cobalt carbonate with a crystallinity of 30% to 80% and a median particle size Dv50 of 3 μm to 22 μm.

5. The method for preparing cobalt tetroxide according to claim 4, characterized in that, The method for preparing cobalt carbonate is as follows: cobalt salt solution and precipitant solution are added concurrently to a reactor containing a bottom liquid, and stirring is started simultaneously to carry out the reaction. When the material in the reactor reaches the upper limit, the feeding and stirring are stopped, and the mixture is allowed to settle. A portion of the supernatant is extracted, and the above feeding, stirring, settling, and extraction of a portion of the supernatant are repeated until the cobalt carbonate obtained reaches the target particle size. After solid-liquid separation, the solid is taken and washed.

6. The method for preparing cobalt tetroxide according to claim 5, characterized in that, The method for preparing cobalt carbonate further includes at least one of the following features: Feature 1: The cobalt salt in the cobalt salt solution is at least one of cobalt chloride, cobalt sulfate, and cobalt nitrate, and the concentration of the cobalt salt solution is 2.0 mol / L to 2.5 mol / L; Feature 2: The precipitant in the precipitant solution is at least one of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, and potassium carbonate, and the concentration of the precipitant solution is 1.0 mol / L to 3.0 mol / L; Feature 3: The cobalt salt solution is added at a flow rate of 20 L / h to 40 L / h, and the precipitant solution is added at a flow rate of 20 L / h to 30 L / h; Feature 4: The base liquid is the precipitant solution; Feature 5: The stirring speed is 200 rpm to 300 rpm, and the reaction temperature is 40℃ to 55℃; Feature 6: The aforementioned extraction of supernatant refers to the extraction of supernatant equivalent to half the capacity of the reactor chamber; Feature 7: The target particle size refers to the median particle size Dv50 of cobalt carbonate, which is 3μm to 22μm.

7. The method for preparing cobalt tetroxide according to claim 4, characterized in that, The pre-sintering process uses a flash dryer with an inlet air temperature of 300℃~400℃, an outlet air temperature of 150℃~180℃, a main unit speed of 20Hz~30Hz, and a feeding frequency of 10Hz~20Hz. Or / and, the calcination is carried out in a rotary kiln, the feeding frequency of the rotary kiln is 3Hz to 9Hz, the rotation frequency of the furnace tube is 12Hz to 15Hz, the temperature is 710℃ to 760℃, and the calcination time is 3h to 5h.

8. A lithium cobalt oxide, characterized in that, The lithium cobalt oxide is obtained by mixing cobalt tetroxide as described in any one of claims 1 to 3 with a lithium source and sintering.

9. A positive electrode sheet, characterized in that, The positive electrode comprises the lithium cobalt oxide as described in claim 8.

10. A battery, characterized in that, The battery includes the positive electrode sheet as described in claim 9.

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