A Mg-F co-doped cobalt tetroxide, its preparation method and application

Abstract

This invention relates to a Mg-F co-doped cobalt tetroxide, its preparation method, and its applications. The Mg-F co-doped cobalt tetroxide contains 2000ppm-5000ppm of Mg and 1000ppm-3000ppm of F. By employing a complexation mechanism between the magnesium dopant and precipitant ions, the problem of poor magnesium precipitation rate control and uneven dopant distribution during doping is solved. This invention improves the structural and electrochemical stability of the material through Mg-F co-doping. The more uniform distribution of the co-doped elements suppresses particle breakage and oxygen evolution during cycling, improves interfacial stability, and effectively enhances the high-voltage electrochemical performance of the material. The resulting lithium-ion battery exhibits high energy density and long-cycle stability.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a Mg-F co-doped cobalt tetroxide, its preparation method, and its application. Background Technology

[0002] With the continuous enrichment of functions in 3C electronic products such as mobile phones, laptops and digital cameras, the power consumption of these products has increased significantly. Lithium cobalt oxide (LCO) materials are widely used in these devices due to their advantages such as high specific capacity, good stability and high compaction density.

[0003] Consumer electronics products have increasingly higher requirements for the capacity of lithium-ion batteries, which necessitates further improvements in the charging voltage of lithium cobalt oxide materials. Cobalt tetroxide, as a precursor material for the positive electrode of lithium cobalt oxide, has material properties that greatly influence the performance of lithium cobalt oxide.

[0004] To further improve the energy density of batteries, bulk doping is one of the most widely studied techniques. Doping elements can suppress anisotropic changes in the structure, inhibit phase transitions in layered LCO structures, increase battery voltage, and effectively improve the thermal stability of the material, thereby enhancing high-voltage cycling performance.

[0005] To improve the energy density of 3C batteries while maintaining stability at high voltages, doping cobalt tetroxide precursors with Mg is an important development direction. The occupancy of Mg at Li sites can improve structural stability and increase Li... + The diffusion rate of ions is improved to prevent the destruction of Co octahedrons, thus ensuring good cycling stability under high pressure. In addition to cation doping, anions such as fluoride ions can also replace trace amounts of O in LCO through small-scale substitution. 2- To improve performance and prevent its precipitation under high pressure.

[0006] In actual production, magnesium doping in cobalt tetroxide faces numerous challenges, specifically the inhomogeneity of the doping process and the uncontrollable Mg precipitation rate. Poor precursor morphology and uniformity significantly negatively impact the performance of subsequent materials. The inhomogeneity of dopants in the precursor leads to regional differences in material properties, potentially making certain regions more susceptible to reduction or oxidation during heat treatment. This results in different phases and properties in different regions, ultimately affecting the capacity and cycle performance of the final material.

[0007] Therefore, how to develop a doped cobalt tetroxide material with uniform doping element distribution, stable material morphology and structure, and its preparation method has become an urgent technical problem to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a Mg-F co-doped cobalt tetroxide, its preparation method, and its application. The Mg-F co-doped cobalt tetroxide of the present invention exhibits more uniform elemental doping, and the co-doping suppresses the breakage of lithium cobalt oxide particles and oxygen evolution during cycling.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a Mg-F co-doped cobalt tetroxide, wherein the doping amount of Mg in the Mg-F co-doped cobalt tetroxide is 2000ppm-5000ppm, for example, it can be 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm or 5000ppm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0011] The doping amount of F in the Mg-F co-doped cobalt tetroxide is 1000ppm-3000ppm, for example, it can be 1000ppm, 1500ppm, 2000ppm, 2500ppm or 3000ppm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] This invention improves the structural and electrochemical stability of the material through Mg-F co-doping. The co-doping of magnesium and fluorine can change the crystal structure of lithium cobalt oxide, making it more stable during charging and discharging. Magnesium ions can be embedded into the lattice of lithium cobalt oxide, reducing the crystal structure instability that may occur under high voltage, while the incorporation of fluorine ions helps to further enhance the overall structural stability of the material. The two work synergistically to improve the structural and electrochemical stability of the lithium cobalt oxide cathode material.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0014] Preferably, the average particle size of the Mg-F co-doped cobalt tetroxide is 15μm-17μm, for example, it can be 15μm, 15.5μm, 16μm, 16.5μm or 17μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] In a second aspect, the present invention provides a method for preparing Mg-F co-doped cobalt tetroxide as described in the first aspect, the method comprising the following steps:

[0016] (1) The first precipitant is obtained by mixing the magnesium source and the carbonate solution;

[0017] (2) Using a carbonate solution as the base liquid, the first precipitant and the cobalt-containing solution are added to the base liquid, and after co-precipitation reaction, magnesium-doped cobalt carbonate is obtained;

[0018] (3) Mix the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2) and calcine it in two steps to obtain Mg-F co-doped cobalt tetroxide.

[0019] This invention first involves complexing the dopant magnesium with precipitant ions. After the magnesium salt is mixed with the precipitant, it first complexes with the precipitant to form complex ions, which are then slowly released with changes in pH to form a co-precipitate with cobalt. This solves the problems of poor control over magnesium precipitation rate and uneven distribution of dopant elements during the doping process, and prepares magnesium-doped cobalt carbonate via a liquid-phase method. Then, a fluorine source is introduced into the magnesium-doped cobalt carbonate using a solid-phase method. Through two-step calcination, the transformation of cobalt carbonate to cobalt tetroxide is achieved, and the uniform distribution of fluorine in cobalt tetroxide is ensured. In the first step, the cobalt carbonate is heated to a low temperature in air, and the initial decomposition reaction of cobalt carbonate occurs, producing cobalt oxide and carbon dioxide gas. The purpose of this stage is to ensure that the cobalt exists in the form of oxide and to initially remove some moisture. The second step of calcination promotes the crystal growth of cobalt oxide by increasing the temperature, thereby optimizing the structure and improving its electrochemical performance.

[0020] Preferably, the magnesium source in step (1) includes any one or a combination of at least two of magnesium nitrate, magnesium sulfate, magnesium carbonate, or magnesium chloride. Typical but non-limiting combinations include combinations of magnesium nitrate and magnesium sulfate, combinations of magnesium sulfate and magnesium carbonate, combinations of magnesium carbonate and magnesium chloride, combinations of magnesium nitrate, magnesium sulfate, and magnesium carbonate, combinations of magnesium sulfate, magnesium carbonate, and magnesium chloride, combinations of magnesium nitrate, magnesium sulfate, and magnesium chloride, and combinations of magnesium nitrate, magnesium sulfate, magnesium carbonate, and magnesium chloride.

[0021] Preferably, the carbonate comprises any one or a combination of at least two of ammonium bicarbonate, ammonium carbonate, sodium carbonate, or sodium bicarbonate. Typical but non-limiting combinations include combinations of ammonium bicarbonate and ammonium carbonate, combinations of ammonium carbonate and sodium carbonate, combinations of sodium carbonate and sodium bicarbonate, combinations of ammonium carbonate, sodium carbonate, and sodium bicarbonate, combinations of ammonium bicarbonate, ammonium carbonate, and sodium bicarbonate, and combinations of ammonium bicarbonate, ammonium carbonate, sodium carbonate, and sodium bicarbonate.

[0022] Preferably, the concentration of metallic Mg in the first precipitant is 0.8 g / L-1.2 g / L, for example, it can be 0.8 g / L, 0.85 g / L, 0.9 g / L, 0.95 g / L, 1.0 g / L, 1.05 g / L or 1.2 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the concentration of carbonate in the first precipitant is 200 g / L-300 g / L, for example, it can be 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, 260 g / L, 270 g / L, 280 g / L, 290 g / L or 300 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0024] Preferably, the concentration of carbonate in the base solution in step (2) is 10 g / L-30 g / L, for example, it can be 10 g / L, 12 g / L, 15 g / L, 18 g / L, 20 g / L, 22 g / L, 25 g / L, 28 g / L or 30 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the concentration of metallic Co in the cobalt-containing solution is 90 g / L-150 g / L, for example, it can be 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, 135 g / L, 140 g / L, 145 g / L or 150 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] Preferably, the cobalt-containing solution comprises a cobalt source and a carbonate solution.

[0027] Preferably, the cobalt source includes any one or a combination of at least two of cobalt nitrate, cobalt sulfate, or cobalt chloride. Typical but non-limiting combinations include a combination of cobalt nitrate and cobalt sulfate, a combination of cobalt sulfate and cobalt chloride, a combination of cobalt nitrate and cobalt chloride, or a combination of cobalt nitrate, cobalt sulfate, and cobalt chloride.

[0028] Preferably, the coprecipitation reaction includes a first coprecipitation reaction and a second coprecipitation reaction.

[0029] Preferably, the reaction conditions for the first step of coprecipitation reaction are as follows: reaction temperature is 40℃-45℃, mass ratio of cobalt-containing solution to first precipitant is 0.2-0.3, pH is 7.8-8.5, stirring speed is 250rpm-300rpm, and the reaction proceeds to the second step of coprecipitation reaction when the D50 of cobalt carbonate particles is 4μm-7μm.

[0030] Preferably, the reaction conditions for the second step coprecipitation reaction are: reaction temperature of 45℃-50℃, mass ratio of cobalt-containing solution to first precipitant of 0.3-0.4, pH of 7.2-7.8, and stirring speed of 100rpm-150rpm.

[0031] The present invention further optimizes the use of a two-step coprecipitation reaction, wherein the first step of the coprecipitation reaction is to prepare seed crystals, and in the second step of the coprecipitation reaction, the seed crystals grow to obtain the desired cobalt carbonate. If only a one-step coprecipitation reaction is used, the surface of the synthesized cobalt carbonate will have phase separation or segregation.

[0032] Preferably, the reaction temperature of the first coprecipitation reaction is lower than the reaction temperature of the second coprecipitation reaction.

[0033] In this invention, the reaction temperature of the first coprecipitation reaction is further controlled to be lower than that of the second coprecipitation reaction, in order to enable Co and Mg to precipitate uniformly.

[0034] Preferably, the mass ratio of the cobalt-containing solution to the first precipitant in the first coprecipitation reaction is less than the mass ratio of the cobalt-containing solution to the first precipitant in the second coprecipitation reaction.

[0035] In this invention, the mass ratio of the cobalt-containing solution to the first precipitant in the first coprecipitation reaction is further controlled to be less than the mass ratio of the cobalt-containing solution to the first precipitant in the second coprecipitation reaction, that is, the amount of the first precipitant is increased in order to enable Co and Mg to precipitate uniformly.

[0036] Preferably, the pH of the first coprecipitation reaction is greater than the pH of the second coprecipitation reaction.

[0037] In this invention, the pH of the first coprecipitation reaction is further controlled to be greater than that of the second coprecipitation reaction, in order to enable Co and Mg to precipitate uniformly.

[0038] When mixing the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2) in step (3), the mass ratio of Co to F is controlled to be 1:0.001-0.003, for example, it can be 1:0.001, 1:0.0015, 1:0.002, 1:0.0025 or 1:0.003, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the fluorine source includes any one or a combination of at least two of calcium fluoride, sodium fluoride, or aluminum fluoride. Typical but non-limiting combinations include combinations of calcium fluoride and sodium fluoride, combinations of sodium fluoride and aluminum fluoride, combinations of calcium fluoride and aluminum fluoride, and combinations of calcium fluoride, sodium fluoride, and aluminum fluoride.

[0040] Preferably, the two-step calcination includes a first-stage calcination and a second-stage calcination.

[0041] Preferably, the two-step calcination is carried out in an air atmosphere.

[0042] Preferably, the calcination temperature in the first stage is 300℃-500℃, for example, it can be 300℃, 320℃, 350℃, 380℃, 400℃, 420℃, 450℃, 480℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the calcination time in the first stage is 1-3 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the calcination temperature in the first stage is 500℃-800℃, for example, it can be 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, 680℃, 700℃, 720℃, 750℃, 780℃ or 800℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0045] Preferably, the calcination time in the first stage is 2h-5h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] This invention further optimizes the use of a two-step calcination method, controlling the calcination temperature of the first stage to be 300℃-500℃ and the calcination temperature of the second stage to be 500℃-800℃. This enables uniform doping of the element F and the conversion of cobalt carbonate to cobalt tetroxide. If the calcination temperature of the first stage is too low, the cobalt carbonate particles cannot be pre-oxidized; if the calcination temperature of the first stage is too high, over-oxidation will hinder subsequent shrinkage; if the calcination temperature of the second stage is too low, the particle shrinkage will be insufficient; if the calcination temperature of the second stage is too high, the particles will be over-burned, causing melting or cracking.

[0047] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0048] (1) Mix magnesium source and carbonate solution to obtain a first precipitant with a concentration of 0.8 g / L-1.2 g / L of metallic Mg and a concentration of 200 g / L-300 g / L of carbonate;

[0049] (2) Using a carbonate solution with a carbonate concentration of 10 g / L-30 g / L as the base liquid, the first precipitant and a cobalt-containing solution with a Co concentration of 90 g / L-150 g / L are added to the base liquid. The first co-precipitation reaction is carried out at 40℃-45℃ with a mass ratio of cobalt-containing solution to first precipitant of 0.2-0.3, pH of 7.8-8.5, and stirring at 250 rpm-300 rpm. When the D50 of the cobalt carbonate particles of the reaction product is 4 μm-7 μm, the second co-precipitation reaction is carried out at 45℃-50℃ with a mass ratio of cobalt-containing solution to first precipitant of 0.3-0.4, pH of 7.2-7.8, and stirring at 100 rpm-150 rpm. When the D50 of the cobalt carbonate particles of the reaction product is 15 μm-17 μm, the reaction is completed. After solid-liquid separation, washing and drying, magnesium-doped cobalt carbonate is obtained.

[0050] (3) Mix the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2), control the mass ratio of Co and F elements to be 1:0.001-0.003, calcine at 300℃-500℃ for 1-3 hours in the first stage, and then calcine at 500℃-800℃ for 2-5 hours in the second stage. Compressed air needs to be introduced during the calcination process, and the gas flow rate is 1L / min-10L / min to obtain Mg-F co-doped cobalt tetroxide.

[0051] Thirdly, the present invention provides a lithium cobalt oxide cathode material, which is prepared according to the Mg-F co-doped cobalt tetroxide method described in the first aspect.

[0052] The lithium cobalt oxide cathode material provided by this invention suppresses particle breakage and oxygen evolution during cycling and exhibits excellent high-voltage electrochemical stability.

[0053] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the lithium cobalt oxide cathode material described in the third aspect.

[0054] The lithium-ion battery prepared from the lithium cobalt oxide cathode material provided by this invention, through co-doping, suppresses the breakage of cathode material particles and oxygen evolution during cycling, improves interface stability, effectively enhances the high-voltage electrochemical performance of the material, and exhibits high energy density and long-cycle stability.

[0055] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0056] Compared with the prior art, the present invention has at least the following beneficial effects:

[0057] (1) The present invention improves the stability of the material structure and electrochemical stability by Mg-F co-doping, which can meet the market demand for high voltage.

[0058] (2) In this invention, magnesium doping element is complexed with precipitant ions, which solves the problem of poor control of magnesium precipitation rate and uneven distribution of doping element during the doping process. Magnesium-doped cobalt carbonate is prepared by liquid phase method. Then, a fluorine source is introduced into magnesium-doped cobalt carbonate by solid phase method. Through two-step calcination, on the one hand, the transformation of cobalt carbonate into cobalt tetroxide is realized, and on the other hand, the fluorine element is uniformly distributed in cobalt tetroxide, which reduces the crystal structure instability that may occur under high voltage and helps to further enhance the overall structural stability of the material.

[0059] (3) The lithium-ion battery prepared by the lithium cobalt oxide cathode material provided by the present invention has the effect of co-doping to suppress the breakage of cathode material particles and oxygen evolution during cycling, improve interface stability, effectively improve the high voltage electrochemical performance of the material, and has high energy density and long cycle stability. Attached Figure Description

[0060] Figure 1 This is a SEM image of Mg-F co-doped cobalt tetroxide prepared in Example 1 of this invention;

[0061] Figure 2 This is a SEM image of the Mg-F co-doped cobalt tetroxide prepared in Comparative Example 2 of this invention. Detailed Implementation

[0062] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0063] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0064] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0065] Example 1

[0066] This embodiment provides a Mg-F co-doped cobalt tetroxide, wherein the doping amount of Mg in the Mg-F co-doped cobalt tetroxide is 3500ppm and the doping amount of F is 2000ppm; the average particle size of the Mg-F co-doped cobalt tetroxide is 16.5μm.

[0067] The preparation method of the Mg-F co-doped cobalt tetroxide includes the following steps:

[0068] (1) Mix magnesium nitrate and ammonium carbonate to obtain a first precipitant with a metal Mg concentration of 1.0 g / L and a carbonate concentration of 250 g / L;

[0069] (2) Using a carbonate solution with an ammonium carbonate concentration of 15 g / L as the base liquid, the first precipitant and cobalt nitrate with a metal Co concentration of 120 g / L were added to the base liquid. The first co-precipitation reaction was carried out at 42°C with a mass ratio of cobalt solution to first precipitant of 0.25, pH of 8.1, and stirring at 280 rpm. When the D50 of the cobalt carbonate particles of the reaction product was 5 μm, the second co-precipitation reaction was carried out at 48°C with a mass ratio of cobalt solution to first precipitant of 0.35, pH of 7.4, and stirring at 120 rpm. When the D50 of the cobalt carbonate particles of the reaction product was 16 μm, the reaction was completed. After solid-liquid separation, washing and drying, magnesium-doped cobalt carbonate was obtained.

[0070] (3) Mix calcium fluoride with the magnesium-doped cobalt carbonate obtained in step (2), control the mass ratio of Co and F elements to be 1:0.002, calcine at 400℃ for 2 hours in the first stage, and then calcine at 700℃ for 3 hours in the second stage. Compressed air needs to be introduced during the calcine process, and the gas flow rate is 3L / min, to obtain Mg-F co-doped cobalt tetroxide.

[0071] Example 2

[0072] This embodiment provides a Mg-F co-doped cobalt tetroxide, wherein the doping amount of Mg in the Mg-F co-doped cobalt tetroxide is 2500ppm and the doping amount of F is 1100ppm; the average particle size of the Mg-F co-doped cobalt tetroxide is 15.6μm.

[0073] The preparation method of the Mg-F co-doped cobalt tetroxide includes the following steps:

[0074] (1) Mix magnesium sulfate and ammonium bicarbonate solutions to obtain a first precipitant with a metal Mg concentration of 0.8 g / L and a carbonate concentration of 200 g / L;

[0075] (2) Using a carbonate solution with an ammonium bicarbonate concentration of 10 g / L as the base solution, the first precipitant and cobalt sulfate with a metal Co concentration of 90 g / L were added to the base solution. The first co-precipitation reaction was carried out at 40°C with a mass ratio of cobalt solution to first precipitant of 0.2, pH of 7.8, and stirring at 250 rpm. When the D50 of the cobalt carbonate particles of the reaction product was 4 μm, the second co-precipitation reaction was carried out at 45°C with a mass ratio of cobalt solution to first precipitant of 0.3, pH of 7.2, and stirring at 100 rpm. When the D50 of the cobalt carbonate particles of the reaction product was 15.2 μm, the reaction was completed. After solid-liquid separation, washing and drying, magnesium-doped cobalt carbonate was obtained.

[0076] (3) Mix sodium fluoride with the magnesium-doped cobalt carbonate obtained in step (2), control the mass ratio of Co and F elements to be 1:0.001, calcine at 300℃ for 3 hours in the first stage, and then calcine at 500℃ for 5 hours in the second stage. Compressed air needs to be introduced during the calcine process, and the gas flow rate is 1L / min to obtain Mg-F co-doped cobalt tetroxide.

[0077] Example 3

[0078] This embodiment provides a Mg-F co-doped cobalt tetroxide, wherein the doping amount of Mg in the Mg-F co-doped cobalt tetroxide is 4500ppm and the doping amount of F is 3000ppm; the average particle size of the Mg-F co-doped cobalt tetroxide is 16.8μm.

[0079] The preparation method of the Mg-F co-doped cobalt tetroxide includes the following steps:

[0080] (1) Mix magnesium chloride and sodium bicarbonate solutions to obtain a first precipitant with a metal Mg concentration of 1.2 g / L and a carbonate concentration of 300 g / L;

[0081] (2) Using a carbonate solution with a sodium bicarbonate concentration of 10 g / L-30 g / L as the base solution, the first precipitant and cobalt chloride with a concentration of 150 g / L of metallic Co were added to the base solution. The first co-precipitation reaction was carried out at 45°C with a mass ratio of cobalt solution to first precipitant of 0.3, pH of 8.5, and stirring at 300 rpm. When the D50 of the cobalt carbonate particles of the reaction product was 7 μm, the second co-precipitation reaction was carried out at 50°C with a mass ratio of cobalt solution to first precipitant of 0.4, pH of 7.8, and stirring at 150 rpm. When the D50 of the cobalt carbonate particles of the reaction product was 16.0 μm, the reaction was completed. After solid-liquid separation, washing and drying, magnesium-doped cobalt carbonate was obtained.

[0082] (3) Mix aluminum fluoride with magnesium-doped cobalt carbonate obtained in step (2), control the mass ratio of Co and F elements to be 1:0.003, calcine at 500℃ for 1 hour in the first stage, and then calcine at 800℃ for 2 hours in the second stage. Compressed air needs to be introduced during the calcine process, and the gas flow rate is 10 L / min to obtain Mg-F co-doped cobalt tetroxide.

[0083] Example 4

[0084] This embodiment provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that the conditions of the second coprecipitation reaction in step (2) are replaced with the same conditions as the first coprecipitation reaction when preparing the Mg-F co-doped cobalt tetroxide, while the other preparation steps remain unchanged.

[0085] Example 5

[0086] This embodiment provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that the conditions of the first step co-precipitation reaction in step (2) are replaced with the same conditions as the second step co-precipitation reaction when preparing the Mg-F co-doped cobalt tetroxide, while the other preparation steps remain unchanged.

[0087] Example 6

[0088] This embodiment provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that the calcination temperature in the first stage of step (3) is 200°C when preparing the Mg-F co-doped cobalt tetroxide, while the other preparation steps remain unchanged.

[0089] Example 7

[0090] This embodiment provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that the calcination temperature in the first stage of step (3) is 800℃ when preparing the Mg-F co-doped cobalt tetroxide, while the other preparation steps remain unchanged.

[0091] Example 8

[0092] This embodiment provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that the calcination temperature in the second stage of step (3) is 1000℃ when preparing the Mg-F co-doped cobalt tetroxide, while the other preparation steps remain unchanged.

[0093] Comparative Example 1

[0094] This comparative example provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that the Mg doping amount is 1000 ppm.

[0095] Comparative Example 2

[0096] This comparative example provides a Mg-F co-doped cobalt tetroxide, which differs from Example 1 only in that step (1) is omitted when preparing the Mg-F co-doped cobalt tetroxide, and step (2) is replaced with the following steps: using a carbonate solution with a carbonate concentration of 10 g / L as the base liquid, equal amounts of magnesium source, cobalt-containing solution and carbonate are added to the base liquid in parallel, and after co-precipitation reaction, magnesium-doped cobalt carbonate is obtained; the conditions of step (3) remain unchanged.

[0097] Application Example 1

[0098] This application example provides a lithium cobalt oxide cathode material, which is prepared using the Mg-F co-doped cobalt tetroxide material of Example 1. The specific preparation method is as follows:

[0099] The Mg-F co-doped cobalt tetroxide material obtained in Example 1 was ball-milled and mixed with lithium carbonate at a molar ratio of 1:1.03. The mixture was then reacted at 700°C for 7 hours in an air atmosphere, followed by heating at 3°C / min, holding at 900°C for 10 hours, and cooling at 5°C / min to obtain lithium cobalt oxide.

[0100] Application Examples 2-8

[0101] Application Examples 2-8 provide a lithium cobalt oxide cathode material, which is prepared by using the Mg-F co-doped cobalt tetroxide material of Examples 2-8, with the other preparation methods remaining unchanged.

[0102] Comparative Application Example 1 - Comparative Application Example 2

[0103] Comparative Application Examples 1 and 2 provide a lithium cobalt oxide cathode material, which is prepared by Mg-F co-doped cobalt tetroxide material as described in Comparative Examples 1 and 2, respectively, with the other preparation methods remaining unchanged.

[0104] test:

[0105] Preparation of positive electrode sheet: First, PVDF binder is dissolved in NMP, and conductive agent and lithium cobalt oxide positive electrode material are added, mixed and dispersed. The mass ratio of lithium cobalt oxide positive electrode material, carbon black and PVDF is 95:3:2. The prepared slurry is uniformly coated on a 10-20μm thick aluminum foil current collector by a coating machine. After drying, rolling and slitting, positive electrode sheet is obtained. The prepared slurry is used with the lithium cobalt oxide positive electrode material prepared by Application Examples 1-8 and Comparative Application Examples 1-2.

[0106] The SEM images of Mg-F co-doped cobalt tetroxide prepared in Example 1 and Comparative Example 2 are shown below. Figure 1 and Figure 2As shown in the figure, the cobalt tetroxide particles prepared in Example 1 are uniform in size, and all elements are directly and uniformly distributed without segregation. In contrast, some cobalt tetroxide particles prepared in Comparative Example 2 show obvious elemental segregation and phase separation. Therefore, it is proven that the cobalt tetroxide material prepared by the present invention effectively suppresses the problems of uneven elemental doping and phase separation, which helps to further improve the cycle stability of lithium cobalt oxide batteries.

[0107] Battery assembly: The negative electrode is graphite, and the electrolyte is dimethyl carbonate, forming a coin cell. Electrochemical performance testing was then conducted at 4.55V: the first-cycle discharge specific capacity was tested within an electrochemical window of 2.5V to 4.55V; subsequently, cycle tests were performed at 0.2C / 0.5C within the same electrochemical window, and the cycle capacity retention after 100 cycles was obtained.

[0108] The lithium cobalt oxide cathode materials prepared in the corresponding use cases and comparative application examples were tested, and the test results are shown in Table 1 below.

[0109] Table 1

[0110]

[0111] The test results show that:

[0112] (1) As can be seen from Application Examples 1-3, the present invention improves the stability of the material structure and electrochemical stability by Mg-F co-doping. By using the method of complexing the doping element magnesium with the precipitant ions, the problem of poor control of magnesium precipitation rate and uneven distribution of doping elements during the doping process is solved. Magnesium-doped cobalt carbonate is prepared by liquid phase method. Then, a fluorine source is introduced into the magnesium-doped cobalt carbonate by solid phase method. Through two-step calcination, on the one hand, the transformation of cobalt carbonate into cobalt tetroxide is realized, and on the other hand, the fluorine element is uniformly distributed in cobalt tetroxide, which helps to further enhance the overall structural stability of the material.

[0113] (2) By comparing Application Example 1 with Application Examples 6-7, it can be seen that the present invention further employs a two-step co-precipitation reaction. In the first step of the co-precipitation reaction, cobalt carbonate seed crystals of suitable particle size are prepared, and the seed crystals grow to obtain the desired cobalt carbonate. If only a one-step co-precipitation reaction is used, the synthesized cobalt carbonate will have phase separation or segregation on the surface.

[0114] (3) By comparing Application Example 1 with Application Examples 8-10, it can be seen that by further controlling the temperature of the first stage calcination to 300℃-500℃ and the temperature of the first stage calcination to 500℃-800℃, the present invention can achieve uniform doping of F element and conversion of cobalt carbonate to cobalt tetroxide. If the first stage calcination temperature is too low, the cobalt carbonate particles cannot be pre-oxidized; if the first stage calcination temperature is too high, the pre-oxidation will be excessive and not conducive to the later shrinkage; if the second stage calcination temperature is too low, the particle shrinkage will be insufficient; if the second stage calcination temperature is too high, the particles will be over-burned, causing melting or cracking, which will ultimately affect the performance of the battery.

[0115] (4) As can be seen from Example 1 and Comparative Application Example 1, the present invention can improve the cycle stability of lithium cobalt oxide materials by further controlling the amount of Mg doping. However, the improvement effect is not obvious when the amount of doping is small.

[0116] (5) As can be seen from Example 1 and Comparative Application Example 2, the present invention mixes magnesium salt with precipitant to form complex ions with precipitant, and then slowly releases them with pH change to form co-precipitate with cobalt, thereby achieving uniform doping; when this mixing method is not used, the precursor is affected by uneven doping or segregation, thus affecting the cycle performance of the battery.

[0117] In summary, this invention enhances the structural and electrochemical stability of the material through Mg-F co-doping. By employing a complexation mechanism between the dopant element magnesium and the precipitant ions, the problem of poor magnesium precipitation rate control and uneven dopant distribution during the doping process is solved. Magnesium-doped cobalt carbonate is prepared via a liquid-phase method. Subsequently, a fluorine source is introduced into the magnesium-doped cobalt carbonate via a solid-phase method. Through two-step calcination, the transformation of cobalt carbonate into cobalt tetroxide is achieved. On the other hand, the fluorine element is uniformly distributed in cobalt tetroxide, reducing the possibility of crystal structure instability under high voltage. The doping further enhances the overall structural stability of the material.

[0118] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A Mg-F co-doped cobalt tetroxide, characterized in that, The doping amount of Mg in the Mg-F co-doped cobalt tetroxide is 2000ppm-5000ppm, and the doping amount of F is 1000ppm-3000ppm. The Mg-F co-doped cobalt tetroxide is obtained by the following preparation method, which includes the following steps: (1) The first precipitant is obtained by mixing the magnesium source and the carbonate solution; (2) Using a carbonate solution as the base liquid, the first precipitant and the cobalt-containing solution are added to the base liquid, and after co-precipitation reaction, magnesium-doped cobalt carbonate is obtained; (3) Mix the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2), and calcine it in two steps to obtain Mg-F co-doped cobalt tetroxide; The coprecipitation reaction includes a first coprecipitation reaction and a second coprecipitation reaction; The reaction conditions for the first step of the co-precipitation reaction are as follows: reaction temperature is 40℃-45℃, mass ratio of cobalt-containing solution to first precipitant is 0.2-0.3, pH is 7.8-8.5, stirring speed is 250rpm-300rpm, and the reaction proceeds to the second step of co-precipitation reaction when the D50 of cobalt carbonate particles is 4μm-7μm. The reaction conditions for the second step coprecipitation reaction are as follows: reaction temperature is 45℃-50℃, mass ratio of cobalt-containing solution to first precipitant is 0.3-0.4, pH is 7.2-7.8, and stirring speed is 100rpm-150rpm. The reaction temperature of the first coprecipitation reaction is lower than the reaction temperature of the second coprecipitation reaction. The mass ratio of the cobalt-containing solution to the first precipitant in the first coprecipitation reaction is less than the mass ratio of the cobalt-containing solution to the first precipitant in the second coprecipitation reaction. The pH of the first coprecipitation reaction is greater than the pH of the second coprecipitation reaction; The two-step calcination includes a first-stage calcination and a second-stage calcination. The calcination temperature in the first stage is 300℃-500℃; The calcination time in the first stage is 1-3 hours; The calcination temperature in the second stage is 500℃-800℃; The second stage of calcination takes 2-5 hours.

2. The Mg-F co-doped cobalt tetroxide according to claim 1, characterized in that, The average particle size of the Mg-F co-doped cobalt tetroxide is 15μm-17μm.

3. A method for preparing Mg-F co-doped cobalt tetroxide according to claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) The first precipitant is obtained by mixing the magnesium source and the carbonate solution; (2) Using a carbonate solution as the base liquid, the first precipitant and the cobalt-containing solution are added to the base liquid, and after co-precipitation reaction, magnesium-doped cobalt carbonate is obtained; (3) Mix the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2), and calcine it in two steps to obtain Mg-F co-doped cobalt tetroxide; The coprecipitation reaction includes a first coprecipitation reaction and a second coprecipitation reaction; The reaction conditions for the first step of the co-precipitation reaction are as follows: reaction temperature is 40℃-45℃, mass ratio of cobalt-containing solution to first precipitant is 0.2-0.3, pH is 7.8-8.5, stirring speed is 250rpm-300rpm, and the reaction proceeds to the second step of co-precipitation reaction when the D50 of cobalt carbonate particles is 4μm-7μm. The reaction conditions for the second step coprecipitation reaction are as follows: reaction temperature is 45℃-50℃, mass ratio of cobalt-containing solution to first precipitant is 0.3-0.4, pH is 7.2-7.8, and stirring speed is 100rpm-150rpm. The reaction temperature of the first coprecipitation reaction is lower than the reaction temperature of the second coprecipitation reaction. The mass ratio of the cobalt-containing solution to the first precipitant in the first coprecipitation reaction is less than the mass ratio of the cobalt-containing solution to the first precipitant in the second coprecipitation reaction. The pH of the first coprecipitation reaction is greater than the pH of the second coprecipitation reaction; The two-step calcination includes a first-stage calcination and a second-stage calcination. The calcination temperature in the first stage is 300℃-500℃; The calcination time in the first stage is 1-3 hours; The calcination temperature in the second stage is 500℃-800℃; The second stage of calcination takes 2-5 hours.

4. The preparation method according to claim 3, characterized in that, The carbonate includes any one or a combination of at least two of ammonium bicarbonate, ammonium carbonate, sodium carbonate, or sodium bicarbonate.

5. The preparation method according to claim 3, characterized in that, The concentration of metallic Mg in the first precipitant is 0.8 g / L-1.2 g / L.

6. The preparation method according to claim 3, characterized in that, The concentration of carbonate in the first precipitant is 200g / L-300g / L.

7. The preparation method according to claim 3, characterized in that, The concentration of carbonate in the bottom solution in step (2) is 10 g / L-30 g / L.

8. The preparation method according to claim 3, characterized in that, The concentration of metallic Co in the cobalt-containing solution is 90 g / L-150 g / L.

9. The preparation method according to claim 3, characterized in that, When mixing the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2) in step (3), the mass ratio of Co and F elements is controlled to be 1:0.001-0.

003.

10. The preparation method according to claim 3, characterized in that, The fluorine source includes any one or a combination of at least two of calcium fluoride, sodium fluoride, or aluminum fluoride.

11. The preparation method according to claim 3, characterized in that, The preparation method includes the following steps: (1) Mix magnesium source and carbonate solution to obtain a first precipitant with a concentration of 0.8 g / L-1.2 g / L of metallic Mg and a concentration of 200 g / L-300 g / L of carbonate; (2) Using a carbonate solution with a carbonate concentration of 10 g / L-30 g / L as the base liquid, the first precipitant and a cobalt-containing solution with a Co concentration of 90 g / L-150 g / L are added to the base liquid. The first co-precipitation reaction is carried out at 40℃-45℃ with a mass ratio of cobalt-containing solution to first precipitant of 0.2-0.3, pH of 7.8-8.5, and stirring at 250 rpm-300 rpm. When the D50 of the cobalt carbonate particles of the reaction product is 4 μm-7 μm, the second co-precipitation reaction is carried out at 45℃-50℃ with a mass ratio of cobalt-containing solution to first precipitant of 0.3-0.4, pH of 7.2-7.8, and stirring at 100 rpm-150 rpm. When the D50 of the cobalt carbonate particles of the reaction product is 15 μm-17 μm, the reaction ends. After solid-liquid separation, washing and drying, magnesium-doped cobalt carbonate is obtained. (3) Mix the fluorine source with the magnesium-doped cobalt carbonate obtained in step (2), control the mass ratio of Co and F elements to be 1:0.001-0.003, calcine at 300℃-500℃ for 1-3 hours in the first stage, and then calcine at 500℃-800℃ for 2-5 hours in the second stage. Compressed air needs to be introduced during the calcination process, and the gas flow rate is 1L / min-10L / min to obtain Mg-F co-doped cobalt tetroxide.

12. A lithium cobalt oxide cathode material, characterized in that, The lithium cobalt oxide cathode material is prepared by Mg-F co-doping of cobalt tetroxide as described in claim 1 or 2.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium cobalt oxide cathode material as described in claim 12.

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