WO2022142327A1 - Aluminum-doped cobaltosic oxide core-shell material and preparation method therefor - Google Patents

Abstract

Disclosed is an aluminum-doped cobaltosic oxide core-shell material. The core is aluminum-doped cobaltosic oxide, and the shell is cobaltosic oxide. The preparation method therefor comprises: firstly, preparing a cobalt carbonate seed slurry in a reaction kettle; simultaneously adding a cobalt salt and aluminum salt mixed solution and a precipitating agent into the reaction kettle for reaction; controlling the reaction temperature to be 50-60°C and the rotational speed to be 600-800 rpm; stopping feeding when particles grow to a median particle size of 18-20 μm; adjusting the reaction temperature to be 45-50°C and the rotational speed to be 400-600 rpm; adding a cobalt salt solution and the precipitating agent for reaction; continuously growing the particles until the median particle size is 20-23 μm; and washing, drying and calcining same to obtain the aluminum-doped cobaltosic oxide core-shell material. The aluminum-doped cobaltosic oxide of the present invention has a core-shell structure, and the shell of the outer layer does not contain Al, so that segregation is unlikely to occur, and the cycle performance of the material can be improved.

Description

A kind of aluminum-doped cobalt tetroxide core-shell material and preparation method thereof technical field

The invention belongs to the field of positive electrode materials for lithium ion batteries, in particular to an aluminum-doped cobalt tetroxide core-shell material and a preparation method thereof.

Background technique

In recent years, people's requirements for the performance of consumer electronic products tend to be smarter, lighter, and have longer standby time. Among them, lighter and longer standby time, these two performances depend on the battery design. It is necessary to design a battery with a smaller volume and a higher energy density, and the energy density depends largely on the positive electrode material in the battery. At present, in 3C electronic products, lithium cobalt oxide has been widely used as the preferred cathode material for small lithium-ion batteries. The compaction density and voltage direction of lithium are unfolded. The production of lithium cobalt oxide is basically prepared by a high temperature solid phase method using lithium carbonate and cobalt tetroxide as raw materials. The performance of lithium cobalt oxide largely depends on the physical indicators of its precursor, cobalt tetroxide, such as particle size distribution, morphology, tap density, and specific surface area. Therefore, it is necessary to develop and research cobalt tetroxide precursor materials that can improve the physicochemical index of lithium cobaltate and improve its electrochemical performance. At present, the problem of heterogeneous nucleation during the synthesis of large particles of cobalt tetroxide has not been well solved in the industry, which will affect the particle size distribution and vibration of lithium cobalt oxide, and thus affect the performance of electrochemical performance.

Publication number CN108217753A discloses a method for preparing a gradient-doped tricobalt tetroxide material. Precipitation of cobalt is obtained under set conditions, and doping elements are added to obtain the doping precipitate through co-precipitation. The precipitate is moderately sintered to obtain a cobalt tetroxide material whose doping concentration gradually increases from the inside to the outside along the radius of the particle. The preparation method is simple and the reaction process is controllable. Structural stability and electrical properties of the material lithium cobaltate at high voltages.

Publication number CN108609666A discloses a preparation method of metal element gradient doped tricobalt tetroxide, provides a kind of preparation method of dopant element center distribution, less outer layer distribution, gradient doped metal element preparation method, can ensure The doping elements are mostly distributed in the cobalt tetroxide lattice, rather than in the form of metal oxides on the surface of the cobalt tetroxide.

The above method has certain beneficial effects on the structural stability of lithium cobaltate from the perspective of element distribution of particles, but does not mention the situation that large particle precursors grow to a certain particle size and will nucleate out of phase to produce small particles. This problem has not been well solved in the industry, and the small particles produced are difficult to separate. Even if separated, it will cause loss of Al content and affect the yield. As a result, its electrical performance is difficult to improve.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide an aluminum-doped cobalt tetroxide core-shell material and a preparation method thereof.

In order to solve the above-mentioned technical problems, the technical scheme proposed by the present invention is:

An aluminum-doped cobalt tetroxide core-shell material, the core is aluminum-doped cobalt tetroxide, the general chemical formula is Co ₃ O ₄ ·xAl ₂ O ₃ , x≤0.5%, the shell is cobalt tetroxide, and the general chemical formula is Co ₃ O ₄ .

In the above-mentioned aluminum-doped cobalt tetroxide core-shell material, preferably, the diameter of the core is 14-22 μm, and the thickness of the shell is 1-3 μm.

In the above-mentioned aluminum-doped cobalt tetroxide core-shell material, preferably, the tap density of the aluminum-doped cobalt tetroxide core-shell material is ≥2.2 g/cm ³ , and the specific surface area is 2.5-5 m ² /g.

As a general inventive concept, the present invention also provides a preparation method of the above-mentioned aluminum-doped cobalt tetroxide core-shell material, comprising the following steps:

(1) Add a precipitant to the reactor as the bottom liquid, add the mixed solution of cobalt salt and aluminum salt, and the precipitant to the reactor simultaneously to react, and stop feeding when the particle grows to a median size of 8 to 11 μm , to obtain cobalt carbonate seed slurry;

(2) The mixed solution of cobalt salt and aluminum salt and the precipitant are simultaneously added to the reaction kettle for reaction, and the reaction temperature is controlled to be 50-60 ° C, and the rotating speed is 600-800 rpm. When the particles grow to a median diameter of 18 to 20 μm Stop feeding later;

(3) adjusting the reaction temperature to be 45-50° C. and the rotating speed to be 400-600 rpm, adding a cobalt salt solution and a precipitant, continuing to grow to a median particle size of 20-23 μm, washing and drying to obtain a semi-finished product of core-shell cobalt carbonate;

(4) calcining the semi-finished product of core-shell cobalt carbonate to obtain a finished product of cobalt tetroxide.

In the above preparation method, preferably, in step (4), the calcination includes a low temperature section and a high temperature section, the temperature of the low temperature section is 400-500 °C, and the temperature of the high temperature section is 750-850 °C.

In the above preparation method, preferably, the calcination time of the low temperature section is 2-5h, and the calcination time of the high temperature section is 2-8h.

In the above-mentioned preparation method, preferably, in step (1), the reaction temperature is controlled to be 50-60° C., the rotating speed of the reactor stirrer is 800-1000 rpm, and the pH of the system in the reactor is 7.8-8.1.

In the above-mentioned preparation method, preferably, in step (2), the pH in the reaction kettle is controlled to be 7.5-7.8.

In the above preparation method, preferably, in step (1) and step (2), the concentration of cobalt salt in the mixed solution of cobalt salt and aluminum salt is 100-120g/L, and the concentration of aluminum salt is 0.7-1.5g /L;

In step (3), the concentration of the cobalt salt solution is 100-120 g/L.

Further preferably, the cobalt salt is at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate; the aluminum salt is at least one of aluminum sulfate, aluminum chloride, and aluminum nitrate.

In the above preparation method, preferably, the precipitating agent is at least one of ammonium bicarbonate and sodium carbonate, and the concentration of the precipitating agent is 200-250 g/L.

Compared with the prior art, the advantages of the present invention are:

(1) The aluminum-doped tricobalt tetroxide of the present invention has a core-shell structure, and the outer shell does not contain Al, which is not easy to produce segregation, and can improve the cycle performance of the material.

(2) the present invention adopts the co-precipitation method to prepare the Al-doped cobalt carbonate with uniform particle size and narrow distribution, and then obtains cobalt tetroxide by the method of high temperature thermal decomposition. The particle size is larger, and at the same time, it can avoid the heterogeneous nucleation of the reaction system and produce a large number of small particles (the doping elements are easy to be enriched in the small particles, thus causing the problem of uneven distribution of aluminum elements in the large and small particles), Doping is more uniform.

(3) The present invention prepares the precursor cobalt salt doped with metal elements by the liquid phase co-precipitation method, so that the metal elements are evenly distributed in the cobalt salt system, and after high temperature decomposition, the precursor cobalt salt with a loose structure is fused into a tight and stable precursor The precursor of cobalt tetroxide.

(4) The present invention adopts the co-precipitation reaction, firstly reducing the rotational speed during the growth process of the cobalt carbonate seed crystal, which greatly suppresses the phenomenon that the nucleus material produces small particles during the growth process, and prepares the nucleus with a larger median diameter. Then start to co-precipitate a layer of cobalt tetroxide, a shell material that does not contain aluminum, on the surface of the core material. This process not only further reduces the rotational speed, but also reduces the temperature and pH value, so that the particle size is not easy to grow while further growing. produce small particles.

(5) The shell of the cobalt tetroxide core-shell structure finally obtained by the present invention does not contain aluminum. By calculating the ratio of cobalt salt and aluminum salt in the core-shell salt solution, controlling the particle size of the core before generating the particle size node of small particles and The thickness of the shell can finally obtain the product with the target doping amount, and the process method has strong controllability.

(6) The core-shell structure cobalt tetroxide prepared by the present invention is used in the positive electrode material, and the cycle performance is better.

Description of drawings

1 is a particle size distribution diagram of the aluminum-doped cobalt tetroxide core-shell material prepared in Example 1.

FIG. 2 is a scanning electron microscope image of the aluminum-doped cobalt tetroxide core-shell material prepared in Example 2. FIG.

3 is a scanning electron microscope image of the aluminum-doped cobalt tetroxide core-shell material prepared in Example 2.

FIG. 4 is a cross-sectional view and EDS spectrum of the aluminum-doped cobalt tetroxide core-shell material prepared in Example 2. FIG.

5 is a scanning electron microscope image of the aluminum-doped cobalt tetroxide core-shell material prepared in Example 2.

6 is a scanning electron microscope image of the aluminum-doped cobalt tetroxide core-shell material prepared in Comparative Example 1.

Detailed ways

In order to facilitate understanding of the present invention, the present invention will be described more comprehensively and in detail below with reference to the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

Example 1:

An aluminum-doped cobalt tetroxide core-shell material of the present invention is spherical, the inner core of the spherical shape is aluminum-doped cobalt tetroxide (Co ₃ O ₄ ·0.1Al ₂ O ₃ ), and the outer shell is cobalt tetroxide (Co ₃ O ₄ ). , the diameter of the core is about 14.13 μm, and the thickness of the shell is about 1 μm. The tap density of the aluminum-doped cobalt tetroxide core-shell material is 2.35 g/cm ³ and the specific surface area is 2.67 m ² /g.

The preparation method of the aluminum-doped cobalt tetroxide core-shell material of the present embodiment includes the following steps:

(1) add 10L precipitation agent ammonium bicarbonate solution (concentration is 230g/L) as bottom liquid in reactor, control temperature of reaction is 55 ℃, and the rotating speed of reactor stirrer is 1000rpm, by cobalt chloride and aluminum sulfate Mixed solution (cobalt concentration is 110g/L, aluminum concentration is 1.21g/L) and ammonium bicarbonate solution (concentration is 230g/L) are added in the reactor simultaneously to react, and the pH in the control reactor is between 7.8-8.1 , when the particles grow to a median diameter of 11 μm, stop feeding to obtain cobalt carbonate seed crystal slurry, let stand, and extract the supernatant;

(2) the mixed solution of cobalt chloride and aluminum sulfate (cobalt concentration is 110g/L, aluminum concentration is 1.21g/L), ammonium bicarbonate solution are added in the reactor simultaneously and react, control reaction temperature is 55 ℃, rotating speed 800rpm, pH between 7.5-7.8, stop feeding when the particles grow to a median size of 18μm;

(3) regulating reaction temperature is 48 ℃, rotating speed is 500rpm, then adds cobalt chloride solution (cobalt concentration is 110g/L) and ammonium bicarbonate solution (concentration is 230g/L) simultaneously, the pH in the control reactor is at 7.5 Between -7.8, continue to grow until the median particle size is 20 μm, wash and dry to obtain the semi-finished cobalt carbonate core-shell structure;

(4) The semi-finished cobalt carbonate with core-shell structure is calcined first at a low temperature of 450 °C for 5 hours, and then at a high temperature of 800 °C for 5 hours to obtain aluminum-doped cobalt tetroxide. Its particle size distribution is shown in Figure 1, and it can be seen from the figure It is found that the D50 of the material is 16.13 μm, and the Span is 0.76. The diameter of the particles prepared by this method is narrow and the particle size distribution is concentrated. The physicochemical indexes of the aluminum-doped cobalt tetroxide are shown in Table 1.

The Al-doped tricobalt tetroxide prepared in this example is mixed with lithium salt, sintered into a lithium cobalt oxide positive electrode material, and assembled into a battery, tested under the test conditions of 3-4.45V, the battery discharge capacity 0.1C is 212.9mAh/g, 40 The second cycle capacity retention rate was 94.6%.

Example 2:

An aluminum-doped cobalt tetroxide core-shell material of the present invention is spherical, the spherical inner core is aluminum-doped cobalt tetroxide (Co ₃ O ₄ ·0.05Al ₂ O ₃ ), and the outer shell is cobalt tetroxide (Co ₃ O ₄ ). , the diameter of the core is about 14.4 μm, and the thickness of the shell is about 2 μm. The tap density of the aluminum-doped cobalt tetroxide core-shell material is 2.38 g/cm ³ and the specific surface area is 2.64 m ² /g.

The preparation method of the aluminum-doped cobalt tetroxide core-shell material of the present embodiment includes the following steps:

(1) in reactor, add the ammonium bicarbonate solution (concentration is 230g/L) of 10L as bottom liquid, control reaction temperature is 60 ℃, rotating speed is 1000rpm, with cobalt chloride and aluminum sulfate mixed solution (cobalt concentration is 110g /L, aluminum concentration is 0.78g/L) and ammonium bicarbonate solution are added to the reaction kettle at the same time for reaction, the pH in the control reaction kettle is between 7.8-8.1, when the particles grow to a median size of 11 μm, stop feeding material to obtain cobalt carbonate seed crystal slurry, let stand, and extract the supernatant.

(2) cobalt chloride and aluminum sulfate mixed solution (cobalt concentration is 110g/L, aluminum concentration is 0.78g/L), ammonium bicarbonate solution are added in the reactor simultaneously and react, control reaction temperature is 60 ℃, rotating speed is At 750 rpm, the pH in the reactor was controlled between 7.5-7.8; when the particles grew to a median size of 20 μm, the feeding was stopped.

(3) regulating reaction temperature is 50 ℃, rotating speed is 600rpm, then adds cobalt chloride solution (cobalt concentration is 110g/L) and ammonium bicarbonate solution simultaneously, the pH in the control reactor is between 7.5-7.8, continues to grow to a median particle size of 22 μm, washing and drying to obtain a semi-finished product of core-shell cobalt carbonate;

(4) The semi-finished product of core-shell cobalt carbonate is calcined, first calcined at a low temperature of 450 °C for 5 hours, and then calcined at a high temperature of 800 °C for 5 hours to obtain an aluminum-doped cobalt tetroxide product. It can be seen from the SEM image that the particles are uniform, and there are no obvious small particles in the field of view. The scanning electron microscope image at high magnification is shown in Figure 5. It can be seen from Figure 5 that the morphology of the aluminum-doped cobalt tetroxide product is good. The physicochemical indexes of the aluminum-doped cobalt tetroxide are shown in Table 1.

The cross-sectional view and EDS spectrum of the aluminum-doped cobalt tetroxide prepared in this example are shown in FIG. 4 . It can be seen from FIG. 4 that the light and shade are the boundary between the core and the shell, and the elements are uniformly distributed inside the core.

The Al-doped tricobalt tetroxide prepared in this example was mixed with lithium salt according to the same conditions as in Example 1, sintered into a lithium cobalt oxide positive electrode material, and assembled into a battery. The battery discharge capacity was 0.1C, 213.9mAh/g, 40 The second cycle capacity retention rate was 94%.

Comparative Example 1:

The aluminum-doped cobalt tetroxide of this comparative example is spherical, the diameter of the precursor is 16.69 μm, the tap density of the aluminum-doped cobalt tetroxide material is 2.07 g/cm ³ , and the specific surface area is 2.13 m ² /g.

The preparation method of the aluminum-doped cobalt tetroxide material of the present comparative example comprises the following steps:

(1) add 10L precipitation agent ammonium bicarbonate solution (concentration is 230g/L) as bottom liquid in reactor, control temperature of reaction is 55 ℃, and the rotating speed of reactor stirrer is 1000rpm, by cobalt chloride and aluminum sulfate Mixed solution (cobalt concentration is 110g/L, aluminum concentration is 1.21g/L) and ammonium bicarbonate solution (concentration is 230g/L) are added in the reactor simultaneously to react, and the pH in the control reactor is between 7.8-8.1 , when the particles grow to a median diameter of 11 μm, stop feeding to obtain cobalt carbonate seed crystal slurry, let stand, and extract the supernatant;

(2) the mixed solution of cobalt chloride and aluminum sulfate (cobalt concentration is 110g/L, aluminum concentration is 1.21g/L), ammonium bicarbonate solution are added in the reactor simultaneously and react, control reaction temperature is 55 ℃, rotating speed It is 800rpm, and the pH in the reaction kettle is controlled between 7.5-7.8. When the particles grow to a median diameter of 20μm, the feeding is stopped;

(3) regulating reaction temperature is 48 ℃, rotating speed is 500rpm, then simultaneously adds the mixed solution of cobalt chloride and aluminum sulfate (cobalt concentration is 110g/L, aluminum concentration is 1.21g/L) and ammonium bicarbonate solution (concentration is 230g/L), the pH in the control reactor is between 7.5-7.8, continue to grow to the median particle diameter and be 22 μm, wash, dry, obtain the cobalt carbonate semi-finished product;

(4) The semi-finished cobalt carbonate was first calcined at a low temperature of 450 °C for 5 hours, and then at a high temperature of 800 °C for 5 hours to obtain aluminum-doped cobalt tetroxide. particles are present. The physicochemical indexes of the aluminum-doped cobalt tetroxide are shown in Table 1.

The Al-doped tricobalt tetroxide prepared in this comparative example was mixed with lithium salt under the same conditions as in Example 1, sintered into a lithium cobalt oxide positive electrode material, and assembled into a battery. The battery discharge capacity was 0.1C, 208.2mAh/g, 40 The second cycle capacity retention rate was 93.2%.

From the comparison of the test process and results of Example 1 and the comparative example, it can be seen that the outer layer of the aluminum-doped cobalt tetroxide secondary spherical particles prepared in the comparative example contains Al, and the Al in the outer layer of the secondary spherical particles is more likely to segregate, which affects the cycle performance of the material. Moreover, there are a large number of fine particles in the cobalt tetroxide particles prepared in the comparative example, which easily causes uneven distribution of aluminum elements in the large and small particles, and also affects the chemical properties of the material.

Table 1 Physical and chemical indexes of aluminum-doped cobalt tetroxide of embodiment and comparative example

	D50(μm)	Span	TD(g/cm 3 )	BET(m 2 /g)	Co(%)	Al(%)
Example 1	16.13	0.76	2.35	2.67	72.75	0.71
Example 2	18.4	0.63	2.38	2.64	72.58	0.44
Comparative Example 1	16.69	0.32	2.07	2.13	72.67	0.60

Claims (10)

1. An aluminum-doped cobalt tetroxide core-shell material, characterized in that the core is aluminum-doped cobalt tetroxide, and its chemical formula is Co ₃ O ₄ ·xAl ₂ O ₃ , x≤0.5%, the shell is cobalt tetroxide, and its chemical The general formula is Co ₃ O ₄ .
2. The aluminum-doped cobalt tetroxide core-shell material according to claim 1, wherein the diameter of the core is 14-22 μm, and the thickness of the shell is 1-3 μm.
3. The aluminum-doped cobalt tetroxide core-shell material according to claim 1, wherein the tap density of the aluminum-doped cobalt tetroxide core-shell material is ≥2.2 g/cm ³ , and the specific surface area is 2.5-5 m ² /g.
4. A method for preparing an aluminum-doped tricobalt tetroxide core-shell material as claimed in any one of claims 1-3, characterized in that, comprising the following steps:

   (1) Add a precipitant to the reaction kettle as the bottom liquid, add the mixed solution of cobalt salt and aluminum salt, and the precipitant to the reaction kettle simultaneously to react, and stop feeding when the particle grows to a median diameter of 8 to 11 μm , to obtain cobalt carbonate seed slurry;

   (2) The mixed solution of cobalt salt and aluminum salt and the precipitant are simultaneously added to the reaction kettle for reaction, and the reaction temperature is controlled to be 50-60 ° C, and the rotating speed is 600-800 rpm. When the particles grow to a median diameter of 18 to 20 μm stop feeding;

   (3) adjust the reaction temperature to be 45-50°C, the rotating speed to be 400-600rpm, add a cobalt salt solution and a precipitant to react, the particles continue to grow to a median diameter of 20-23 μm, wash and dry to obtain core-shell cobalt carbonate semi-finished products;

   (4) calcining the semi-finished product of core-shell cobalt carbonate to obtain an aluminum-doped cobalt tetroxide core-shell material.
5. The preparation method according to claim 4, wherein in step (4), the calcination includes a low temperature section and a high temperature section, the temperature of the low temperature section is 400-500°C, and the temperature of the high temperature section is 750°C ~850°C.
6. The preparation method according to claim 5, wherein the calcination time of the low temperature section is 2-5h, and the calcination time of the high temperature section is 2-8h.
7. The preparation method according to claim 4, wherein, in step (1), the control reaction temperature is 50-60 DEG C, the rotating speed of the reactor stirrer is 800-1000rpm, and the pH of the system in the reactor is 7.8-8.1 .
8. The preparation method according to claim 4, characterized in that, in step (2), the pH in the reaction kettle is controlled to be 7.5-7.8.
9. The preparation method according to any one of claims 4-8, wherein in step (1) and step (2), the concentration of cobalt salt in the mixed solution of cobalt salt and aluminum salt is 100-120g /L, the concentration of aluminum salt is 0.7-1.5g/L;

   In step (3), the concentration of the cobalt salt solution is 100-120 g/L.
10. The preparation method according to any one of claims 4-8, wherein the precipitating agent is at least one of ammonium bicarbonate and sodium carbonate, and the concentration of the precipitating agent is 200-250 g/L.

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