CN115676909A - Cobalt carbonate precursor and preparation method and application thereof - Google Patents

Cobalt carbonate precursor and preparation method and application thereof Download PDF

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CN115676909A
CN115676909A CN202211313012.0A CN202211313012A CN115676909A CN 115676909 A CN115676909 A CN 115676909A CN 202211313012 A CN202211313012 A CN 202211313012A CN 115676909 A CN115676909 A CN 115676909A
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cobalt carbonate
solution
cobalt
coating layer
concentration
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CN115676909B (en
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刘文泽
于杨
许开华
张坤
段小波
赵亚强
陈颖
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Jingmen GEM New Material Co Ltd
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Abstract

The invention provides a cobalt carbonate precursor, a preparation method and application thereof, wherein the cobalt carbonate comprises an Al-doped cobalt carbonate matrix and a cobalt carbonate coating layer coated on the surface of the Al-doped cobalt carbonate matrix, and the cobalt carbonate coating layer contains Al and other doping elements. According to the invention, the surface of the Al-doped cobalt carbonate substrate is coated with the cobalt carbonate coating layer containing Al and other doped elements, and after calcination, the elements of the surface coating layer and the substrate elements can diffuse mutually to form the multifunctional surface gradient coating layer, so that aluminum segregation on the particle surface can be effectively inhibited, cracking of particles during calcination can be prevented, the surface appearance can be improved, the anode material can be effectively prevented from being corroded by electrolyte, and the cycle and rate performance of the battery can be improved.

Description

Cobalt carbonate precursor and preparation method and application thereof
Technical Field
The invention belongs to the technical field of anode materials, and particularly relates to a cobalt carbonate precursor, and a preparation method and application thereof.
Background
Lithium cobaltate is widely applied to 3C digital electronic products, along with the diversification of functions and the diversification of use scenes of portable equipment, the market has higher and higher requirements on the energy density of a lithium cobaltate battery, and the common process in the industry at present is to increase the charging voltage of a positive electrode material by doping an element Al so as to increase the energy density of the battery.
There are many ways of doping Al, al salt can be added in the stage of calcining for preparing Li, and Al salt can also be added in the stage of synthesizing cobalt carbonate to realize element doping through coprecipitation. However, as the amount of Al is increased, the problems of local occurrence of lamellar segregation and calcination cracking on the particle surface during the reaction process, washing and calcination are mostly solved by improving the surface morphology or increasing the reaction temperature.
CN113307308A discloses a doped large-particle cobalt carbonate and a preparation method thereof, the large-particle cobalt carbonate is doped with metal elements, the shape of primary particles is conical, the primary particles form spherical secondary particles, and the preparation method comprises the steps of nucleation, concentration, growth in a seed crystal kettle and seed crystal kettle-by-kettle growth. The doped large-particle cobalt carbonate has high crystallinity, is beneficial to uniform distribution of doped element aluminum, has high tap density and narrow particle size distribution, and is beneficial to reducing aluminum segregation phenomenon. However, this is only applicable to the method of doping with Al at a low concentration.
CN114014374A discloses a preparation method and application of a cobalt carbonate composite precursor with a core-shell structure and a sintered lithium cobaltate coating, the method is realized by the following steps: 1) Solution preparation and synthesis; 2) Primary sintering; 3) Secondary sintering; 4) Ball milling; 5) And sintering for the third time to obtain the lithium cobaltate with the coated CNTs and the core-shell structure. However, the coating layer obtained by the method is not uniform and is inconsistent with the crystal lattice structure of the matrix, so that the coating layer is easy to fall off, and the body performance is influenced by three times of sintering.
Therefore, how to inhibit aluminum segregation and avoid poor morphology and calcination cracking caused by high aluminum doping is an urgent technical problem to be solved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a cobalt carbonate precursor, and a preparation method and application thereof. The invention provides a cobalt carbonate precursor with a cobalt carbonate coating layer, which takes cobalt carbonate as a matrix, and the surface of the cobalt carbonate precursor comprises the cobalt carbonate coating layer containing a first doping element. After calcination, the elements of the cobalt oxide surface coating layer and the matrix elements are mutually diffused to form multifunctional surface gradient coating, so that aluminum segregation on the surface of particles can be effectively inhibited, cracking of the particles during calcination is prevented, the surface appearance is improved, the anode material can be effectively prevented from being corroded by electrolyte, and the cycle and rate performance of the battery are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides cobalt carbonate, which comprises an Al-doped cobalt carbonate substrate and a cobalt carbonate coating layer coated on the surface of the Al-doped cobalt carbonate substrate, wherein the cobalt carbonate coating layer contains Al and other doping elements.
The invention provides a cobalt carbonate precursor which takes aluminum-doped cobalt carbonate as a matrix and has a cobalt carbonate coating layer containing Al element and other doped elements on the surface. The coating containing the Al element can effectively prevent the segregation of Al in the matrix, and other elements are supplemented to replace Al to protect the particle structure and provide corresponding functions, so that the multifunctional surface coating is obtained, the Li transmission speed of the anode material can be accelerated, the capacity is improved, the corrosion of electrolyte is relieved, and the cycle and rate performance are improved.
In the present invention, if the cobalt carbonate coating layer is not coated on the surface of the cobalt carbonate substrate, problems such as segregation of local flaky Al and cracking of particles occur on the surface of the particles in the subsequent calcination step.
It should be noted that the main composition of the surface coating layer contains cobalt carbonate, and if the surface coating layer is replaced by a pure compound of a doping element as a coating layer, the lattice difference is too large, the coating layer is easy to fall off, and the capacity of the cathode material is reduced.
Preferably, the other doping elements in the cobalt carbonate coating layer comprise any one of Mn, ni, mg, zr or La or a combination of at least two thereof.
Preferably, the amount of Al doped in the Al-doped cobalt carbonate matrix is 8000ppm to 20000ppm, such as 8000ppm, 9000ppm, 10000ppm, 11000ppm, 12000ppm, 13000ppm, 14000ppm, 15000ppm, 16000ppm, 17000ppm, 18000ppm, 19000ppm or 20000ppm and the like.
Preferably, the content of Al in the cobalt carbonate coating layer is 10-50%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or the like, of the amount of Al doped in the Al-doped cobalt carbonate matrix, based on 100% by mass of the cobalt carbonate coating layer.
In the present invention, if the content of the Al element in the cobalt carbonate coating layer is too small, the effect of modifying the material is weakened, whereas if the content is too large, the effect of preventing segregation is not exerted.
Preferably, the content of other doping elements in the cobalt carbonate coating layer is the difference between the doping amount of Al in the cobalt carbonate matrix and the content of Al in the cobalt carbonate coating layer, wherein the mass of the cobalt carbonate matrix is 100%. If the content of other doping elements in the cobalt carbonate coating layer is larger than the difference value, the specific capacity of the material can be reduced; and the content of other doping elements in the cobalt carbonate coating layer is less than the difference, so that the supporting effect is weakened, and the capacity, the first effect and the cycle performance of the battery prepared by the cobalt carbonate coating layer are reduced.
Preferably, the content of the other doping elements in the cobalt carbonate coating layer is 50% -90% of the Al doping amount in the Al-doped cobalt carbonate matrix, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%.
Preferably, the content of the other doping elements in the cobalt carbonate matrix is less than 0.05%, such as 0.01%, 0.02%, 0.03%, 0.04%, or the like, based on 100% by mass of the Al-doped cobalt carbonate matrix.
Preferably, the thickness of the cobalt carbonate coating is 1-2 μm, such as 1 μm, 1.5 μm, or 2 μm, etc.
In the present invention, if the thickness of the cobalt carbonate coating layer is too thin, the cobalt carbonate coating layer is liable to fall off during the calcination process, and the problems of segregation and cracking cannot be effectively suppressed, while if the thickness is too thick, the electrochemical performance of the body is affected.
In a second aspect, the present invention provides a method for preparing cobalt carbonate as described in the first aspect, the method comprising:
co-precipitation reaction is carried out by adopting metal solution containing Co and Al and alkaline solution to prepare cobalt carbonate, when cobalt carbonate particles grow to be close to a preset particle size, any one of (a) or (b) is carried out, and then the reaction is continued to obtain the cobalt carbonate, wherein,
(a) Changing the metal solution into a first coating solution, wherein the first coating solution comprises the following components: cobalt salt solution, al and other doping elements;
(b) And replacing part of the metal solution with a second coating solution to obtain a mixed coating solution, wherein the components of the second coating solution comprise Al and other doping elements.
In the invention, a Co and Al-containing metal solution and an alkaline solution are used as raw materials of a cobalt carbonate precursor, the raw materials are added into a reaction container for coprecipitation reaction, when the particle size of cobalt carbonate particles grows to be close to a preset particle size, the original Co and Al-containing metal solution is completely replaced by a cobalt salt-containing solution and a first coating solution of Al and other doping elements, or part of the Co and Al-containing metal solution is replaced by a second coating solution of Al and other doping elements, and the coprecipitation reaction is continued to finally obtain the cobalt carbonate precursor with the preset particle size. The coating process is realized by replacing the raw materials in the coprecipitation reaction process, so that Al segregation can be prevented, full coating can be realized on the surface of the cobalt carbonate substrate, complete coverage is achieved, and a better protection effect is realized.
Preferably, the approximately preset particle size is: the difference between the predetermined particle size and the actual particle size is 1-2 μm, for example 1 μm, 1.5 μm or 2 μm, etc.
In the invention, if the difference between the preset particle size and the actual particle size is too large, the thickness of the coating layer is affected.
Preferably, the method for preparing cobalt carbonate by using Co and Al containing metal solution and alkaline solution to perform coprecipitation reaction comprises the following steps:
(1) Respectively preparing a metal solution containing Co and Al, an alkaline solution and a base solution;
(2) Adding a base solution into a reaction container, adding a metal solution containing Co and Al and an alkaline solution in a cocurrent mode, and carrying out coprecipitation reaction.
The preparation sequence of the cobalt-containing solution, the alkaline solution and the base solution is not limited, and the preparation of the solution can be carried out sequentially or synchronously.
In one embodiment, the base solution is placed inside a container, and the Co and Al containing metal solution and the alkaline solution are added to the container in a cocurrent manner to perform the coprecipitation reaction. And (2) along with the continuous reaction, the particle size is gradually close to the preset particle size, when the particle size is close to the preset particle size, part of the Co and Al containing metal solution is replaced to be a second coating solution, at the moment, the mixed solution of the second coating solution and the cobalt containing solution and the alkaline solution are continuously added into the container for reaction, finally, a cobalt carbonate precursor with the preset particle size is obtained, and a cobalt carbonate coating layer containing Al and other doping elements is formed on the surface of the cobalt carbonate substrate.
Preferably, the Co-containing solution comprises CoCl 2 、CoSO 4 Or CoNO 3 Any one or a combination of at least two of them.
Preferably, the Al-containing compound comprises AlCl and AlSO 4 Or AlNO 3 Any one or a combination of at least two of them.
Preferably, the Co concentration of the Co and Al containing metal solution is 90-130g/L, such as 90g/L, 95g/L, 100g/L, 105g/L, 110g/L, 115g/L, 120g/L, 125g/L, 130g/L, or the like.
Preferably, the Co and Al containing metal solution has an Al concentration of 1-2g/L, such as 1g/L, 1.2g/L, 1.4g/L, 1.6g/L, 1.8g/L, 2g/L, or the like.
Preferably, the alkaline solution is a carbonate and/or bicarbonate containing salt solution, preferably an ammonium bicarbonate solution.
Preferably, the concentration of the alkaline solution is 220-260g/L, such as 220g/L, 225g/L, 230g/L, 235g/L, 240g/L, 245g/L, 250g/L, 255g/L, 260g/L, and the like.
Preferably, the base solution has a concentration of 0-50g/L and does not contain 0g/L, such as 5g/L, 10g/L, 15g/L, 20g/L, 25g/L, 30g/L, 35g/L, 40g/L, 45g/L, or 50g/L, and the like.
Preferably, after step (a) is performed, the first coating solution has an Al concentration of 0.2-1g/L, such as 0.2g/L, 0.4g/L, 0.6g/L, 0.8g/L, or 1g/L, etc.
Preferably, after step (b) is performed, the Al concentration of the mixed coating solution is 0.2-1g/L, such as 0.2g/L, 0.4g/L, 0.6g/L, 0.8g/L, or 1g/L.
In the present invention, if the content of the Al element in the coating liquid is too small, the effect of modifying the material is weakened, and if the content is too large, the effect of preventing segregation is not exerted.
Preferably, the temperature of the co-precipitation reaction is 35-55 ℃, such as 35 ℃, 40 ℃, 45 ℃, 50 ℃, or 55 ℃ and the like.
Preferably, the pH of the co-precipitation reaction is 7.2-7.6, such as 7.2, 7.3, 7.4, 7.5, or 7.6, etc.
Preferably, the coprecipitation reaction is carried out under stirring conditions, with a rotation speed of 100-300r/min, such as 100r/min, 150r/min, 200r/min, 250r/min or 300r/min, etc.
Preferably, the temperature of the continued reaction is 40-55 ℃, such as 40 ℃, 45 ℃, 50 ℃ or 55 ℃ and the like.
Preferably, the pH of the continued reaction is 7.2-7.6, such as 7.2, 7.3, 7.4, 7.5 or 7.6, etc.
In a third aspect, the present invention provides a cobalt oxide material obtained by calcining cobalt carbonate as described in the first aspect.
Preferably, the cobalt oxide material comprises a cobalt oxide inner core and a cobalt oxide coating layer positioned on the surface of the cobalt oxide inner core, wherein Al and other doping elements in the cobalt oxide coating layer are distributed in a gradient manner.
According to the invention, the elements of the surface coating layer can diffuse with the elements of the matrix after calcination to form surface gradient coating, so that the function diversification of the surface coating layer is realized, the problems of surface segregation, appearance cracking and the like can be effectively avoided, the Li transmission speed of the anode material can be increased, the corrosion of electrolyte can be relieved, and the cycle and rate performance can be improved.
Preferably, the coating is a full coating.
In the invention, the coating mode is full coating, so that particle cracking and Al segregation can be prevented.
Preferably, the preparation method of the cobalt oxide material comprises the following steps: preparing cobalt carbonate by the method of the second aspect, aging and calcining to obtain cobalt oxide.
In the invention, the aging is to stand for a period of time, so that the particle size of the cobalt oxide obtained by calcination is more uniform.
Preferably, the aging time is 1-2h, such as 1h, 1.5h, 2h, or the like.
Preferably, the temperature of the calcination is 500-800 ℃, such as 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, or 800 ℃ and the like.
Preferably, the calcination is carried out for a period of 1 to 4 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, etc.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(1) Mixing a cobalt salt solution and an Al salt solution to prepare a solution A with the Co concentration of 90-130g/L and the Al concentration of 1-2g/L; preparing an alkaline solution B with the concentration of 220-260g/L; preparing a solution C containing a cobalt salt solution, al and any one or combination of at least two of Mn, ni, mg, zr or La, wherein the concentration of Al is 0.2-1g/L; preparing a base solution of the reaction container, wherein the concentration of the base solution is 0-50g/L and does not contain 0g/L;
(2) Adding a base solution into a reaction container, adding the solution A and the solution B in a parallel flow mode, and carrying out coprecipitation reaction at the temperature of 35-55 ℃ and under the condition that the pH value is 7.2-7.6;
(3) When the cobalt carbonate particles grow to be close to the preset particle size, changing the solution A into a solution C, and continuing to react to obtain cobalt carbonate;
(4) And aging the obtained cobalt carbonate particles for 1-2h, and calcining at 500-800 ℃ for 1-4h to obtain the cobalt oxide.
In a fourth aspect, the present invention provides a lithium ion battery, wherein a positive electrode of the lithium ion battery comprises the cobalt oxide of the third aspect.
The recitation of numerical ranges herein includes not only the above-recited values, but also any values between any of the above-recited numerical ranges not recited, and for brevity and clarity, is not intended to be exhaustive of the specific values encompassed within the range.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a cobalt carbonate precursor with a cobalt carbonate coating, which takes cobalt carbonate as a matrix, and the surface of the cobalt carbonate precursor is the cobalt carbonate coating containing a first doping element. After calcination, elements of the cobalt oxide surface coating layer and matrix elements can be mutually diffused to form a multifunctional surface gradient coating layer, so that aluminum segregation on the surface of particles is effectively inhibited, cracking of the particles during calcination is prevented, the surface appearance is improved, the anode material is effectively prevented from being corroded by electrolyte, the Li transmission speed of the anode material is increased, and the cycle and rate performance of the battery are improved.
Drawings
Fig. 1 is a schematic structural diagram of a cobalt carbonate precursor provided in embodiment 1 of the present invention.
Fig. 2 is a scanned image of the coated and modified cobalt carbonate particles provided in example 1 of the present invention, with a magnification of 10000 times.
Fig. 3 is a scanned image of the coated and modified cobalt oxide particles provided in example 1 of the present invention, with a magnification of 10000 times.
Wherein, 1-cobalt carbonate matrix; 2-cobalt carbonate coating.
Detailed Description
The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The present embodiment provides a cobalt carbonate, as shown in fig. 1, the cobalt carbonate includes a cobalt carbonate substrate 1 and a cobalt carbonate coating layer 2 coated on the surface of the cobalt carbonate substrate 1, the cobalt carbonate coating layer 2 contains elements Al and Mn, and the cobalt carbonate substrate 1 contains element Al. The content of the Al element in the cobalt carbonate coating layer 2 was 4200ppm, the content of the Mn element was 9800ppm, and the content of the Al element in the cobalt carbonate base body 1 was 14000ppm, wherein the content of the Al element in the cobalt carbonate coating layer 2 was 30% of the content of the Al element in the cobalt carbonate base body 1, and the content of the Mn element was 70% of the content of the Al element in the cobalt carbonate base body 1.
The embodiment also provides a preparation method of the cobalt carbonate and the cobalt oxide obtained by calcination, and the preparation method specifically comprises the following steps:
(1) Adding CoCl 2 Solution and Al 2 (SO 4 ) 3 Mixing the solutions to prepare a solution A with the Co concentration of 90g/L and the Al concentration of 1.35 g/L; preparing an ammonium bicarbonate solution B with the concentration of 220 g/L; preparation of a composition containing CoCl 2 The first coating liquid C comprises Al element and Mn element, wherein the Al concentration of the first coating liquid C is 0.6g/L; preparing a base solution ammonium bicarbonate solution of the reaction container, wherein the concentration is 15g/L;
(2) Adding a base solution into a reaction container, adding the solution A and the solution B in a parallel flow mode, and carrying out coprecipitation reaction at the temperature of 45 ℃ and the pH value of 7.4 at the rotating speed of 150r/min;
(3) When the cobalt carbonate particles grow to 15 micrometers, replacing the solution A with a first coating solution C, adjusting the reaction temperature to 50 ℃, adjusting the pH to 7.4, continuing the reaction to obtain a cobalt carbonate precursor with the particle size of 16.5 micrometers, wherein the thickness of the cobalt carbonate coating is 1.5 micrometers.
Fig. 2 is a scanned graph of the coated and modified cobalt carbonate particles provided in example 1 of the present invention, and it can be seen from the graph that after coating modification, the cobalt carbonate coating layer is dense and uniform, and complete coating is achieved.
The embodiment also provides cobalt oxide, which is prepared by calcining the cobalt carbonate serving as a precursor, and the preparation method comprises the following steps:
the obtained cobalt carbonate particles were aged for 1.5h and calcined at 650 ℃ for 2.5h to obtain cobalt oxide.
Fig. 3 is a scanned graph of the coated and modified cobalt oxide particles provided in example 1 of the present invention, and it can be seen from the graph that, after the coating and modification, the cobalt oxide particles have compact surfaces, uniform crystal forms, no cracking, and good coating effects.
Example 2
The embodiment provides cobalt carbonate, which comprises a cobalt carbonate matrix and a cobalt carbonate coating layer coated on the surface of the cobalt carbonate matrix, wherein the cobalt carbonate coating layer contains elements Al and Mn, and the cobalt carbonate matrix contains element Al. The content of Al element in the cobalt carbonate coating layer is 4000ppm, the content of Mn element is 4000ppm, and the content of Al element in the cobalt carbonate matrix is 8000ppm, wherein the content of Al element in the cobalt carbonate coating layer is 50% of the content of Al element in the cobalt carbonate matrix, and the content of Mn element is 50% of the content of Al element in the cobalt carbonate matrix.
The embodiment also provides a preparation method of the cobalt carbonate and the cobalt oxide obtained by calcination, and the preparation method specifically comprises the following steps:
(1) Adding CoSO 4 Solution and Al 2 NO 3 Mixing the solutions to prepare a solution A with the Co concentration of 110g/L and the Al concentration of 1.5 g/L; preparing an ammonium bicarbonate solution B with the concentration of 240 g/L; preparation of a composition containing CoSO 4 The concentration of the first coating liquid C containing Al element and Mn element is 0.3g/L; preparing a base solution ammonium bicarbonate solution of the reaction container, wherein the concentration is 25g/L;
(2) Adding a base solution into a reaction container, adding the solution A and the solution B in a parallel flow mode, and carrying out coprecipitation reaction at the temperature of 35 ℃ and the pH value of 7.2 at the rotating speed of 100r/min;
(3) When the cobalt carbonate particles grow to 16 mu m, the solution A is replaced by the first coating solution C, the reaction temperature is adjusted to 40 ℃, the pH value is 7.2, the reaction is continued, a cobalt carbonate precursor with the particle size of 17 mu m is obtained, and the thickness of the cobalt carbonate coating is 1 mu m.
The embodiment also provides cobalt oxide, which is prepared by calcining the cobalt carbonate serving as a precursor, and the preparation method comprises the following steps:
the obtained cobalt carbonate particles were aged for 1h and calcined at 500 ℃ for 4h to obtain cobalt oxide.
Example 3
The embodiment provides cobalt carbonate, which comprises a cobalt carbonate matrix and a cobalt carbonate coating layer coated on the surface of the cobalt carbonate matrix, wherein the cobalt carbonate coating layer contains elements Al, mn and Ni, and the cobalt carbonate matrix contains element Al. The content of Al element in the cobalt carbonate coating layer is 2000ppm, the content of Mn element is 10000ppm, the content of Ni element is 8000ppm, and the content of Al element in the cobalt carbonate matrix is 20000ppm, wherein the content of Al element in the cobalt carbonate coating layer is 10% of the content of Al element in the cobalt carbonate matrix, and the sum of the content of Mn element and the content of Ni element is 90% of the content of Al element in the cobalt carbonate matrix.
The embodiment also provides a preparation method of the cobalt carbonate and the cobalt oxide obtained by calcination, and the preparation method specifically comprises the following steps:
(1) Reacting CoNO 3 Solution and AlCl 3 Mixing the solutions to prepare a solution A with the Co concentration of 130g/L and the Al concentration of 2g/L; preparing an ammonium bicarbonate solution B with the concentration of 260g/L; formulation containing CoNO 3 The concentration of the first coating liquid C of Al element, mn element and Ni element is 1g/L; preparing a base solution ammonium bicarbonate solution of the reaction container, wherein the concentration is 50g/L;
(2) Adding a base solution into a reaction container, adding the solution A and the solution B in a cocurrent flow mode, and carrying out coprecipitation reaction at the temperature of 55 ℃ and the pH value of 7.6 at the rotating speed of 300r/min;
(3) When the cobalt carbonate particles grow to 18 mu m, the solution A is replaced by the first coating solution C, the reaction temperature is adjusted to 40 ℃, the pH value is 7.2, the reaction is continued, a cobalt carbonate precursor with the particle size of 20 mu m is obtained, and the thickness of the cobalt carbonate coating is 2 mu m.
The embodiment also provides cobalt oxide, which is prepared by calcining the cobalt carbonate serving as a precursor, and the preparation method comprises the following steps:
the obtained cobalt carbonate particles are aged for 2h and calcined at 800 ℃ for 1h to obtain cobalt oxide.
Example 4
The difference between this example and example 1 is that the content of Al element in the cobalt carbonate coating layer is 1120ppm, that is, 8% of the content of Al element in the cobalt carbonate matrix.
The remaining preparation methods and parameters were in accordance with example 1.
Example 5
This example is different from example 1 in that the content of Al element in the cobalt carbonate coating layer was 7700ppm, that is, 55% of the content of Al element in the cobalt carbonate matrix.
The remaining preparation methods and parameters were in accordance with example 1.
Example 6
This example is different from example 1 in that the content of Mn element in the cobalt carbonate coating layer was 5600ppm, that is, 40% of the content of Al element in the cobalt carbonate matrix.
The remaining preparation methods and parameters were in accordance with example 1.
Example 7
The difference between this example and example 1 is that the content of Mn element in the cobalt carbonate coating layer is 13300ppm, that is, 95% of the content of Al element in the cobalt carbonate matrix.
The remaining preparation methods and parameters were in accordance with example 1.
Example 8
This example is different from example 1 in that the thickness of the cobalt carbonate coating layer obtained in step (3) was 0.5 μm
The remaining preparation methods and parameters were in accordance with example 1.
Example 9
This example is different from example 1 in that the thickness of the cobalt carbonate coating layer obtained in step (3) was 2.5 μm
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 1
The comparative example is different from example 1 in that Al element is contained in the preparation in the step (1)Elemental and Mn without CoCl 2 The first coating liquid C of (1).
The remaining preparation methods and parameters were in accordance with example 1.
Comparative example 2
This comparative example differs from example 1 in that CoCl-containing was prepared in step (1) 2 And a first coating liquid C of Al element.
The remaining preparation methods and parameters were in accordance with example 1.
And (3) performance testing:
preparing a positive active material by using the cobalt oxide prepared in the embodiments 1 to 9 and the comparative examples 1 to 2 as a precursor, and assembling the positive active material into a lithium ion battery, wherein the preparation method of the positive electrode is that the cobalt oxide precursor and a lithium salt are mixed according to a proportion and calcined at 800 ℃ for 24 hours to prepare the positive active material, the active material, a conductive agent and a binder are uniformly mixed and coated on a cut aluminum foil according to a proportion of 75;
the negative electrode is a lithium sheet;
the electrolyte comprises the following components: 1mol/L LiPF 6 The solvent is a mixed solvent of DMC, EC, DEC and EMC according to a volume ratio of 1;
the type of the diaphragm: celgard 2400;
testing specific capacity: charging at 0.1C, discharging at 0.1C, testing specific capacity under a voltage window of 2-4.5V, and recording the specific discharge capacity;
testing the cycle performance: the cycle performance is tested under the conditions of 0.1C charging, 0.2C discharging and 2-4.5V voltage window;
and (3) testing rate performance: and (4) testing the rate capability under the conditions of 0.5C charging, 1C discharging and a voltage window of 2-4.5V, and recording the specific discharge capacity.
TABLE 1
Figure BDA0003907793870000141
And (3) analysis:
the data results of examples 1-9 show that after being coated by the cobalt carbonate coating containing Al and other doping elements, al segregation on the particle surface is inhibited, the surface morphology of the particle is improved, and the performance of the prepared lithium ion battery is obviously improved.
As can be seen from the comparison of the data of example 1 with those of examples 4 and 5, when the content of Al element in the cobalt carbonate coating layer is too low, the modification effect on the material is weakened, and thus the specific capacity and the cycle stability of the battery are reduced, and the rate performance is also poor, whereas when the content of Al element in the cobalt carbonate coating layer is too high, the function of inhibiting Al segregation is weakened, resulting in a significant reduction in the rate performance of the battery.
As can be seen from the comparison of the data obtained in example 1 with those obtained in examples 6 and 7, the stability and rate capability of the battery are reduced when the content of other doping elements in the cobalt carbonate coating layer is too low, while the specific capacity of the material is reduced and the cycling stability of the battery is reduced when the content of other doping elements in the cobalt carbonate coating layer is too high.
Comparing the data results of example 1 and examples 8 and 9, it is known that when the thickness of the cobalt carbonate coating layer is too thin, the calcination process is easy to fall off, thereby effectively suppressing segregation and solving the cracking problem, and thus the specific capacity of the material and the cycle stability and rate capability of the battery are reduced, while when the thickness of the cobalt carbonate coating layer is too thick, the electrochemical performance of the battery body is affected, so that the specific capacity of the material is reduced, and the cycle stability and rate capability of the battery are reduced.
As can be seen from the comparison of the data results of example 1 and comparative example 1, when the coating is a coating of Al and other doping elements and does not contain cobalt carbonate, al segregation on the particle surface cannot be effectively inhibited, the surface morphology is improved, the specific capacity of the material is significantly reduced, and the cycling stability and rate capability of the battery are also significantly reduced.
As can be seen from the comparison of the data results of example 1 and comparative example 2, the cobalt carbonate coating layer does not contain doping elements other than Al, and thus the multifunction of the surface coating layer cannot be realized, so that the specific capacity of the material is significantly reduced, and the cycling stability and rate capability of the battery are significantly reduced.
In conclusion, after the coating, the segregation of Al is inhibited, the specific capacity of the material is obviously improved, and the cycle performance is also greatly improved, so that the coating is stable and is not easy to fall off, and the situations such as the structural collapse of the anode material can be effectively prevented; the rate performance improvement effect is obvious, and the coating layer can provide a rapid lithium ion transmission channel to serve as a lithium ion transmission transfer station, so that the rate performance of the material is optimized.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of the raw materials of the product of the present invention, and the addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (10)

1. The cobalt carbonate is characterized by comprising an Al-doped cobalt carbonate matrix and a cobalt carbonate coating layer coated on the surface of the Al-doped cobalt carbonate matrix, wherein the cobalt carbonate coating layer contains Al and other doping elements.
2. Cobalt carbonate according to claim 1, characterized in that the further doping element in the cobalt carbonate coating layer comprises any one or a combination of at least two of Mn, ni, mg, zr or La;
preferably, the Al doping amount in the Al-doped cobalt carbonate matrix is 8000ppm-20000ppm;
preferably, the content of Al in the cobalt carbonate coating layer is 10-50% of the Al doping amount in the Al-doped cobalt carbonate matrix, wherein the mass of the cobalt carbonate coating layer is 100%;
preferably, the content of other doping elements in the cobalt carbonate coating layer is the difference between the doping amount of Al in the cobalt carbonate matrix and the content of Al in the cobalt carbonate coating layer, wherein the mass of the cobalt carbonate matrix is 100%;
preferably, the content of other doping elements in the cobalt carbonate coating layer is 50% -90% of the Al doping amount in the Al-doped cobalt carbonate substrate;
preferably, the content of other doping elements in the cobalt carbonate matrix is less than 0.05 percent based on 100 percent of the mass of the Al-doped cobalt carbonate matrix;
preferably, the thickness of the cobalt carbonate coating layer is 1-2 μm.
3. A method for preparing cobalt carbonate according to any one of claims 1 or 2, comprising:
co-precipitation reaction is carried out by adopting metal solution containing Co and Al and alkaline solution to prepare cobalt carbonate, when cobalt carbonate particles grow to be close to a preset particle size, any one of (a) or (b) is carried out, and then the reaction is continued to obtain the cobalt carbonate, wherein,
(a) Changing the metal solution into a first coating solution, wherein the first coating solution comprises the following components: cobalt salt solution, al and other doping elements;
(b) Replacing part of the metal solution with a second coating solution to obtain a mixed coating solution, wherein the components of the second coating solution comprise Al and other doped elements;
preferably, the approximately preset particle size is: the difference between the preset particle size and the actual particle size is 1-2 μm.
4. The preparation method according to claim 3, wherein the method for preparing the cobalt carbonate by using the Co and Al containing metal solution and the alkaline solution to perform the coprecipitation reaction comprises the following steps:
(1) Respectively preparing a metal solution containing Co and Al, an alkaline solution and a base solution;
(2) Adding a base solution into a reaction container, adding a metal solution containing Co and Al and an alkaline solution in a cocurrent mode, and carrying out coprecipitation reaction.
5. The production method according to claim 3 or 4, wherein the Co-and Al-containing metal solution includes a Co-containing compound and an Al-containing compound;
preferably, the Co-containing compound comprises CoCl 2 、CoSO 4 Or CoNO 3 Any one or a combination of at least two of;
preferably, the Al-containing compound comprises AlCl and AlSO 4 Or AlNO 3 Any one or a combination of at least two of;
preferably, the Co concentration of the Co-and Al-containing metal solution is 90-130g/L;
preferably, the Al concentration of the Co-and Al-containing metal solution is 1-2g/L;
preferably, the alkaline solution is a carbonate and/or bicarbonate containing salt solution, preferably an ammonium bicarbonate solution;
preferably, the concentration of the alkaline solution is 220-260g/L;
preferably, the concentration of the base solution is 0-50g/L, and 0g/L is not contained;
preferably, after step (a), the first coating solution has an Al concentration of 0.2-1g/L;
preferably, after performing step (b), the Al concentration of the mixed coating solution is 0.2-1g/L.
6. The method according to any one of claims 3 to 5, wherein the temperature of the coprecipitation reaction is 35 to 55 ℃;
preferably, the pH of the coprecipitation reaction is 7.2 to 7.6;
preferably, the coprecipitation reaction is carried out under the condition of stirring, and the rotating speed of stirring is 100-300r/min;
preferably, the temperature of the continuous reaction is 40-55 ℃;
preferably, the pH of the continued reaction is 7.2 to 7.6.
7. A cobalt oxide material obtained by calcining cobalt carbonate according to any one of claims 1 to 3;
preferably, the cobalt oxide material comprises a cobalt oxide inner core and a cobalt oxide coating layer positioned on the surface of the cobalt oxide inner core, wherein Al and other doping elements in the cobalt oxide coating layer are distributed in a gradient way;
preferably, the coating is a full coating.
8. A method for preparing a cobalt oxide material according to claim 7, wherein the method for preparing a cobalt oxide material comprises:
preparing cobalt carbonate by the method of any one of claims 3 to 6, aging and calcining to obtain cobalt oxide;
preferably, the aging time is 1-2h;
preferably, the temperature of the calcination is 500-800 ℃;
preferably, the calcination time is 1-4h.
9. The method of manufacturing according to claim 8, comprising the steps of:
(1) Mixing a cobalt salt solution and an Al salt solution to prepare a solution A with the Co concentration of 90-130g/L and the Al concentration of 1-2g/L; preparing an alkaline solution B with the concentration of 220-260g/L; preparing a solution C containing a cobalt salt solution, al and any one or combination of at least two of Mn, ni, mg, zr or La, wherein the concentration of Al is 0.2-1g/L; preparing a base solution of the reaction container, wherein the concentration of the base solution is 0-50g/L and does not contain 0g/L;
(2) Adding a base solution into a reaction container, adding the solution A and the solution B in a cocurrent mode, and carrying out coprecipitation reaction at the temperature of 35-55 ℃ and under the condition that the pH value is 7.2-7.6;
(3) When the cobalt carbonate particles grow to be close to the preset particle size, changing the solution A into a solution C, and continuing to react to obtain cobalt carbonate;
(4) And aging the obtained cobalt carbonate particles for 1-2h, and calcining at 500-800 ℃ for 1-4h to obtain the cobalt oxide.
10. A lithium ion battery comprising the cobalt oxide material of claim 7 in a positive electrode thereof.
CN202211313012.0A 2022-10-25 2022-10-25 Cobalt carbonate precursor and preparation method and application thereof Active CN115676909B (en)

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