An inner-tight outer-loose type cobaltosic oxide, a preparation method and application thereof

Abstract

This invention provides a cobalt tetroxide with a compact inner structure and a loose outer structure, its preparation method, and its application. The preparation method includes the following steps: first, a reaction solution containing seed crystals is prepared; then, a second cobalt-aluminum mixed salt solution and a second precipitant solution are co-flowed into the reaction solution containing seed crystals to perform a crystal growth stage, obtaining a reaction solution containing a first intermediate; subsequently, a salt solution containing doped elements, a third cobalt-aluminum mixed salt solution, and a third precipitant solution are co-flowed into the reaction solution containing the first intermediate to perform a second co-precipitation reaction, obtaining a second intermediate; finally, the intermediate is calcined to obtain the cobalt tetroxide with a compact inner structure and a loose outer structure. This preparation method, by controlling the reaction conditions in stages, obtains a cobalt tetroxide with a compact inner structure and a loose outer structure, meeting the requirements for high tap density, high structural strength, and good conductivity, thereby improving the energy density and electrochemical performance of lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of cathode precursor material technology, specifically relating to an internally compact and externally loose type of cobalt tetroxide, its preparation method, and its application. Background Technology

[0002] With the continuous development of technology, the improvement of energy density of lithium-ion batteries, as a key component of energy storage, has become a focus in many research and application fields. Cathode materials, as an important component of lithium-ion batteries, have conductivity and compaction density that are key factors affecting battery cycle performance and energy density.

[0003] On the one hand, to improve the conductivity of cathode materials, researchers typically employ techniques such as element doping and surface coating to significantly enhance the overall conductivity. However, these methods often suffer from uneven distribution of doping elements and coating layers. Furthermore, while higher doping levels can increase capacity, they may disrupt the overall crystal structure, thus reducing conductivity and electrochemical performance. On the other hand, to increase the energy density of lithium-ion batteries, existing technologies disclose the ability to control the size and shape of cathode material particles to achieve close packing, thereby increasing compaction density and significantly improving battery energy density. However, these particle gradation methods are no longer sufficient to meet the requirements of high-voltage lithium cobalt oxide. The performance of cathode materials largely depends on the performance of the precursor, whose quality directly determines the final product's energy density, cycle life, and other core electrochemical properties.

[0004] Therefore, how to prepare a high-voltage lithium cobalt oxide precursor with high tap density, high conductivity and good structural stability, so that the prepared lithium cobalt oxide can have better cycle performance and rate performance while maintaining high capacity, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a cobalt tetroxide with an internally compact and externally loose structure, its preparation method, and its applications. The preparation method provided by the present invention obtains a cobalt tetroxide with an internally compact and externally loose structure by controlling the reaction conditions in stages, thereby meeting the requirements for high tap density, high structural strength, and good conductivity. This allows for improved energy density and electrochemical performance of lithium-ion batteries without the need for particle size distribution.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing cobalt tetroxide with a tight inner structure and a loose outer structure, the method comprising the following steps: S1. The first cobalt-aluminum mixed salt solution and the first precipitant solution are fed into the reaction base liquid in parallel to carry out the nucleation stage of the first coprecipitation reaction, and a reaction solution containing seed crystals is obtained. The reaction substrate includes a first cobalt-aluminum mixed salt solution; S2. The second cobalt-aluminum mixed salt solution and the second precipitant solution are fed into the reaction solution containing the seed crystals in parallel to carry out the growth stage of the first co-precipitation reaction, and a reaction solution containing the first intermediate is obtained. S3. The salt solution containing the doped element, the third cobalt-aluminum mixed salt solution, and the third precipitant solution are fed into the reaction solution containing the first intermediate in parallel to carry out a second coprecipitation reaction to obtain the second intermediate; S4. The second intermediate is calcined to obtain the internally compact and externally loose type of cobalt tetroxide; The feed flow rate of the first cobalt-aluminum mixed salt solution is greater than that of the second cobalt-aluminum mixed salt solution, and the feed flow rate of the first precipitant solution is less than that of the second precipitant solution.

[0007] This invention, by separately controlling the specific reaction conditions at different co-precipitation stages, prepared a high-tap-density cobalt tetroxide with a compact internal structure and a loose, porous external structure. This structure can better adapt to the stress deformation generated by charging and discharging at high voltages. Simultaneously, the loose outer shell structure doped on the surface improves the conductivity and structural stability of the material, thereby enhancing the electrochemical performance of the prepared lithium cobalt oxide cathode material under high voltages. When used in lithium-ion batteries, it can achieve high energy density and excellent cycle stability, as specifically shown below: (1) In the nucleation stage of the first coprecipitation reaction, the present invention uses an aqueous solution containing a first cobalt-aluminum mixed salt solution as the reaction base liquid, which can increase the supersaturation around the first cobalt-aluminum mixed salt feed solution and control the morphology of the formed seed crystals to meet the later structural design. This allows the prepared lithium cobalt oxide cathode material to be used directly without particle gradation to maximize space utilization, thereby better improving the energy density of lithium-ion batteries.

[0008] (2) In the growth stage of the first coprecipitation reaction, the present invention controls the feed flow rate of the second cobalt-aluminum mixed salt solution to be less than that of the first cobalt-aluminum mixed salt solution, and the feed flow rate of the second precipitant solution to be greater than that of the first precipitant solution, thereby further regulating the growth rate and sphericity of the crystal, thereby achieving an internally tight and externally loose structure, and improving the uniformity of aluminum element distribution.

[0009] (3) In order to improve the structural strength of the lithium cobalt oxide cathode material during the second co-precipitation reaction, the present invention performs element doping on the surface of the precursor material to support the material structure and meet the conductivity requirements in the later stage, thereby preventing the subsequent loose shell structure from collapsing.

[0010] Preferably, in step S1, the feed flow rate of the first cobalt-aluminum mixed salt solution is 50L / h to 70L / h, for example, it can be 50L / h, 52L / h, 55L / h, 58L / h, 60L / h, 62L / h, 65L / h, 68L / h or 70L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0011] Preferably, in step S1, the concentration of cobalt ions in the first cobalt-aluminum mixed salt solution is 90 g / L to 130 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 or 130 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0012] Preferably, in step S1, the concentration of aluminum ions in the first cobalt-aluminum mixed salt solution is 1 g / L to 2.5 g / L, for example, it can be 1 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, 2.2 g / L or 2.5 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] Preferably, in step S1, the feed flow rate of the first precipitant solution is 50L / h to 70L / h, for example, it can be 50L / h, 52L / h, 55L / h, 58L / h, 60L / h, 62L / h, 65L / h, 68L / h or 70L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Preferably, in step S1, the concentration of the first precipitant solution is 180 g / L to 250 g / L, for example, it can be 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L, 205 g / L, 210 g / L, 215 g / L, 220 g / L, 225 g / L, 230 g / L, 235 g / L, 240 g / L, 245 g / L, or 250 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, in step S1, the pH of the reaction substrate is 2 to 7, for example, it can be 2, 3, 4, 5, 6 or 7, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, in step S1, the nucleation stage of the first coprecipitation reaction is carried out under the first stirring. The stirring speed of the first stirring is 100 r / min to 200 r / min, for example, it can be 100 r / min, 120 r / min, 150 r / min, 180 r / min or 200 r / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Most existing coprecipitation methods use an aqueous solution of the precipitant as the base liquid. This maintains a stable supersaturation level, promotes the formation of uniform crystal nuclei, and thus achieves the desired product with good sphericity. Unlike existing technologies, this invention uses an aqueous solution containing a first cobalt-aluminum mixed salt solution as the reaction base liquid during the nucleation stage of the first coprecipitation reaction. This increases the supersaturation around the first cobalt-aluminum mixed salt solution. Combined with a larger feed flow rate of the first cobalt-aluminum mixed salt solution and a lower stirring speed, a large number of irregular crystal nuclei can be formed to meet the later requirement of a dense inner and loose outer crystal structure.

[0018] Preferably, in step S1, the temperature of the nucleation stage of the first coprecipitation reaction is 50℃~60℃, for example, it can be 50℃, 52℃, 55℃, 58℃ or 60℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] In this invention, in step S1, the nucleation stage of the first coprecipitation reaction takes 1 to 4 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, in step S1, the pH value of the nucleation stage of the first coprecipitation reaction is 5 to 7, for example, it can be 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8 or 7, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, in step S1, the D of the seed crystal V The particle size is 0.5μm to 2μm, for example, it can be 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm or 2μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, in step S2, the feed flow rate of the second cobalt-aluminum mixed salt solution is 20L / h to 30L / h, for example, it can be 20L / h, 22L / h, 25L / h, 28L / h or 30L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, in step S2, the concentration of cobalt ions in the second cobalt-aluminum mixed salt solution is 90 g / L to 130 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 or 130 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, in step S2, the concentration of aluminum ions in the second cobalt-aluminum mixed salt solution is 1 g / L to 2.5 g / L, for example, it can be 1 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, 2.2 g / L or 2.5 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, in step S2, the feed flow rate of the second precipitant solution is 60L / h to 90L / h, for example, it can be 60L / h, 65L / h, 70L / h, 75L / h, 80L / h, 85L / h or 90L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, in step S2, the concentration of the second precipitant solution is 180 g / L to 250 g / L, for example, it can be 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L, 205 g / L, 210 g / L, 215 g / L, 220 g / L, 225 g / L, 230 g / L, 235 g / L, 240 g / L, 245 g / L, or 250 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] Preferably, in step S2, the growth stage of the first coprecipitation reaction is carried out under a second stirring. The stirring speed of the second stirring is 200 r / min to 250 r / min, for example, it can be 200 r / min, 210 r / min, 220 r / min, 230 r / min, 240 r / min or 250 r / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, in step S2, the temperature of the growth stage of the first coprecipitation reaction is 30℃~40℃, for example, it can be 30℃, 32℃, 35℃, 38℃ or 40℃, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, in step S2, the pH value of the growth stage of the first coprecipitation reaction is 7~8, for example, it can be 7, 7.2, 7.5, 7.8 or 8, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0030] In the growth stage of the first coprecipitation reaction, this invention reduces the feed flow rate of the second cobalt-aluminum mixed salt solution and increases the feed flow rate of the second precipitant solution. At the same time, it combines a lower growth temperature and a higher stirring speed to achieve directional growth of a loose outer shell on the surface of the seed crystal. Furthermore, the larger feed flow rate of the second precipitant solution can prevent aluminum segregation, which is beneficial for the formation of cobalt tetroxide with uniform aluminum distribution.

[0031] If the feed flow rate of the second cobalt-aluminum mixed salt solution is greater than that of the first cobalt-aluminum mixed salt solution, the sphericity of the seed crystals will be rapidly repaired, and the internally tight and externally loose structure will not be formed, resulting in a lower compaction density of the prepared lithium cobalt oxide cathode material.

[0032] If the temperature of the growth stage of the first coprecipitation reaction is not lower than the temperature of the nucleation stage of the first coprecipitation reaction, the sphericity of the precursor particles obtained will be poor. If the temperature is too high, it will lead to uneven distribution of aluminum elements, making the structure of the obtained lithium cobalt oxide cathode material unstable.

[0033] Preferably, in step S2, the D of the first intermediate V 50 The particle size is 7μm~10μm, for example, it can be 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm or 10μm, etc., not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] Preferably, in step S3, the feed flow rate of the salt solution containing the doped element is 10L / h to 30L / h, for example, it can be 10L / h, 12L / h, 15L / h, 18L / h, 20L / h, 22L / h, 25L / h, 28L / h or 30L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, in step S3, the concentration of dopant ions in the salt solution containing dopant elements is 0.5 g / L to 5 g / L, for example, it can be 0.5 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] This invention enables effective doping of the surface layer of cobalt tetroxide by controlling the feed flow rate of the salt solution containing doped elements and the concentration of the doped element ions, thereby increasing its conductivity and structural stability.

[0037] Preferably, the doping element includes any one or a combination of at least two of nickel, magnesium, zirconium, yttrium, or niobium.

[0038] Preferably, the feed flow rate of the third cobalt-aluminum mixed salt solution is greater than the feed flow rate of the first cobalt-aluminum mixed salt solution.

[0039] This invention increases the feed flow rate of the third cobalt-aluminum mixed salt solution, enabling the particles to grow rapidly, thus making the resulting growth layer gradually looser.

[0040] Preferably, in step S3, the feed flow rate of the third cobalt-aluminum mixed salt solution is 100L / h to 150L / h, for example, it can be 100g / L, 105g / L, 110g / L, 115g / L, 120g / L, 125g / L, 130g / L, 135g / L, 140g / L, 145g / L or 150g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] This invention increases the feed flow rate of the third cobalt-aluminum mixed salt solution, enabling rapid particle growth and the formation of a loose outer shell structure.

[0042] Preferably, in step S3, the concentration of cobalt ions in the third cobalt-aluminum mixed salt solution is 90 g / L to 130 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 or 130 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, in step S3, the concentration of aluminum ions in the third cobalt-aluminum mixed salt solution is 1 g / L to 2.5 g / L, for example, it can be 1 g / L, 1.2 g / L, 1.5 g / L, 1.8 g / L, 2 g / L, 2.2 g / L or 2.5 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] Preferably, in step S3, the feed flow rate of the third precipitant solution is 50L / h to 70L / h, for example, it can be 50L / h, 52L / h, 55L / h, 58L / h, 60L / h, 62L / h, 65L / h, 68L / h or 70L / h, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, in step S3, the concentration of the third precipitant solution is 180 g / L to 250 g / L, for example, it can be 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L, 205 g / L, 210 g / L, 215 g / L, 220 g / L, 225 g / L, 230 g / L, 235 g / L, 240 g / L, 245 g / L, or 250 g / L, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, in step S3, the second coprecipitation reaction is carried out under a third stirring, and the stirring speed of the third stirring is 200 r / min to 250 r / min, for example, it can be 200 r / min, 210 r / min, 220 r / min, 230 r / min, 240 r / min or 250 r / min, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] Preferably, in step S3, the temperature of the second coprecipitation reaction is 40℃~50℃, for example, it can be 40℃, 42℃, 45℃, 48℃ or 50℃, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0048] Preferably, in step S3, the pH value of the second coprecipitation reaction is 7~8, for example, it can be 7, 7.2, 7.5, 7.8 or 8, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, in step S3, the D of the second intermediate VThe particle size of 50 is 10μm to 12μm, for example, it can be 10μm, 10.5μm, 10.8μm, 11μm, 11.5μm, 11.8μm or 12μm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, in step S4, the calcination treatment includes a first calcination treatment and a second calcination treatment performed sequentially.

[0051] Preferably, the temperature of the first calcination treatment is 250℃~350℃, and the time of the first calcination treatment is 60min~120min.

[0052] Specifically, the temperature of the first calcination treatment can be, for example, 250℃, 280℃, 300℃, 320℃ or 350℃, and the time of the first calcination treatment can be, for example, 60min, 70min, 80min, 90min, 100min, 110min or 120min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] Preferably, the heating rate of the first calcination treatment is 1℃ / min to 5℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the temperature of the second calcination treatment is 600℃~700℃, and the time of the second calcination treatment is 30min~180min.

[0055] Specifically, the temperature of the second calcination treatment can be, for example, 600℃, 620℃, 650℃, 680℃ or 700℃, and the time of the second calcination treatment can be, for example, 30min, 50min, 80min, 100min, 120min, 150min or 180min, etc., not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0056] Preferably, the heating rate of the second calcination treatment is 5℃ / min to 10℃ / min, for example, it can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] This invention promotes the formation of cobalt tetroxide with a compact inner core and a loose outer layer by controlling the specific conditions of two calcination processes. Due to the difference in growth rates between the particle core and surface, their crystallinity differs; specifically, the core has better crystallinity, while the surface layer has poorer crystallinity. The more crystalline core precursor, due to its higher reactivity, reacts more readily at lower calcination temperatures. Therefore, to achieve the compact inner core and loose outer layer structure, the first calcination process is performed to remove moisture and allow the internal particles to undergo a slow, deep oxidation reaction. The surface precursor, due to its lower reactivity and the presence of numerous ions, which improves its temperature resistance, does not react during the first calcination. During the second calcination, as the calcination temperature increases, the core precursor begins to melt and grow, gradually becoming denser, while the surface precursor also begins to oxidize with the rising temperature. Due to the faster heating rate, the surface oxidation produces a large amount of carbon dioxide, resulting in a loose and porous morphology for the surface precursor.

[0058] In a second aspect, the present invention provides a cobalt tetroxide with a tight inner structure and a loose outer structure, wherein the cobalt tetroxide with a tight inner structure and a loose outer structure is prepared by the preparation method of the cobalt tetroxide with a tight inner structure and a loose outer structure according to the first aspect.

[0059] Preferably, the tap density of the inner-tight and outer-loose type cobalt tetroxide is 2.6 g / cm³. 3 ~2.9g / cm 3 For example, it can be 2.6 g / cm³. 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 2.85g / cm 3 Or 2.9g / cm 3 The term "etc." is not limited to the listed values; it also applies to other unlisted values ​​within the range.

[0060] Preferably, the specific surface area of ​​the internally compact and externally loose cobalt tetroxide is 5 m². 2 / g~8m 2 / g, such as 5m 2 / g、6m 2 / g、7m 2 / g or 8m 2 / g, etc., are not limited to the listed values; other unlisted values ​​within this range also apply.

[0061] The tap density of the cobalt tetroxide precursor obtained by the preparation method provided in this invention is 2.6 g / cm³. 3 ~2.9g / cm 3 Specific surface area is 5m²2 / g~8m 2 / g can further improve the specific capacity, cycle performance and structural stability of lithium cobalt oxide cathode materials under high voltage.

[0062] In this invention, the inner-tight and outer-loose cobalt tetroxide includes a core and a doped outer shell covering the surface of the core.

[0063] In this invention, the doping amount of the doped element in the doped shell is 11000ppm~13000ppm, for example, it can be 11000ppm, 11500ppm, 12000ppm, 12500ppm or 13000ppm, etc., and is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] Thirdly, the present invention provides a lithium cobalt oxide, which is prepared by calcining cobalt tetroxide of the inner-tight and outer-loose type according to the second aspect with a lithium source.

[0065] Specifically, the preparation method of the lithium cobalt oxide includes: ball milling cobalt tetroxide of the internally compact and externally loose type as described in the second aspect with a lithium source at a molar ratio of cobalt to lithium of 1:(1~1.02), and then calcining at 900℃~1000℃ for 6h~8h to obtain lithium cobalt oxide.

[0066] Fourthly, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode comprises lithium cobalt oxide as described in the third aspect.

[0067] In this invention, the electrolytes include, for example, liquid electrolytes, gel electrolytes, and solid electrolytes.

[0068] 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.

[0069] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing cobalt tetroxide with a compact internal structure and a loose external structure. By controlling the specific reaction conditions at different co-precipitation stages, a high-tap-density cobalt tetroxide with a compact internal structure and a loose, porous external structure is obtained. This structure can better adapt to the stress deformation generated by charging and discharging at high voltages. At the same time, the loose outer shell structure doped on the surface can improve the conductivity and structural stability of the material, thereby enhancing the electrochemical performance of the prepared lithium cobalt oxide cathode material under high voltages. When used in lithium-ion batteries, it can achieve high energy density and excellent cycle stability, as shown below: (1) In the nucleation stage of the first coprecipitation reaction, the present invention uses an aqueous solution containing a first cobalt-aluminum mixed salt solution as the reaction base liquid, which can increase the supersaturation around the first cobalt-aluminum mixed salt feed solution and control the morphology of the formed seed crystals to meet the later structural design. This allows the prepared lithium cobalt oxide cathode material to be used directly without particle gradation to maximize space utilization, thereby better improving the energy density of lithium-ion batteries.

[0070] (2) In the growth stage of the first coprecipitation reaction, the present invention controls the feed flow rate of the second cobalt-aluminum mixed salt solution to be less than that of the first cobalt-aluminum mixed salt solution, and the feed flow rate of the second precipitant solution to be greater than that of the first precipitant solution, thereby further regulating the growth rate and sphericity of the crystal, thereby achieving an internally tight and externally loose structure, and improving the uniformity of aluminum element distribution.

[0071] (3) During the second co-precipitation reaction, the present invention optimizes the feed flow rate of the third cobalt-aluminum mixed salt solution to enable rapid particle growth, thereby making the resulting growth layer gradually loose. In order to improve the structural strength of the lithium cobalt oxide cathode material, the present invention further performs element doping on the surface of the precursor material to support the material structure and meet the conductivity requirements in the later stage, thereby preventing the subsequent loose shell structure from collapsing. Attached Figure Description

[0072] Figure 1 The image shown is an SEM image of the internally compact and externally loose type of cobalt tetroxide provided in Example 1, with a scale bar of 30 μm.

[0073] Figure 2 The image shown is a SEM image of the internally compact and externally loose type of cobalt tetroxide provided in Example 1, with a scale bar of 3 μm. Detailed Implementation

[0074] The technical solution of the present invention will be further described below with reference to specific embodiments and accompanying drawings. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0075] Example 1 This embodiment provides a cobalt tetroxide with a tight inner structure and a loose outer structure, and a method for preparing the same. The preparation method includes the following steps: S1. Prepare an aluminum-cobalt mixed salt solution with an Al concentration of 1.5 g / L and a Co concentration of 130 g / L by mixing aluminum chloride and cobalt chloride. Prepare a precipitant solution with a mass concentration of 250 g / L by mixing ammonium bicarbonate and water. Prepare a reaction base solution by mixing the above aluminum-cobalt mixed salt solution with water. The pH value of the reaction base solution is 4.5.

[0076] The cobalt-aluminum mixed salt solution and the precipitant solution were fed concurrently into the reaction substrate at feed rates of 60 L / h and 60 L / h, respectively. The first co-precipitation reaction nucleation stage was carried out for 2 hours at 55°C and pH=6, with a stirring speed of 150 r / min, yielding a reaction solution containing seed crystals; wherein, the D of the seed crystals... V 50 particles have a diameter of 2μm.

[0077] S2. A cobalt-aluminum mixed salt solution with an Al concentration of 1.5 g / L and a Co concentration of 130 g / L, and an ammonium bicarbonate precipitant solution with a mass concentration of 250 g / L, were fed concurrently into the above-mentioned reaction solution containing seed crystals at feed flow rates of 25 L / h and 80 L / h, respectively. The first co-precipitation reaction growth stage was carried out for 100 h at 35 °C and pH=7, with a stirring speed of 200 r / min, to obtain a reaction solution containing the first intermediate; wherein, the first intermediate D... V 50 particles have a diameter of 8 μm.

[0078] S3. Prepare a salt solution containing doped elements, with a Ni concentration of 1.5 g / L and a Nb concentration of 1 g / L, by mixing nickel chloride and niobium chloride.

[0079] The above-mentioned salt solution containing doped elements, a cobalt-aluminum mixed salt solution with an Al concentration of 1.5 g / L and a Co concentration of 130 g / L, and an ammonium bicarbonate precipitant solution with a mass concentration of 250 g / L were fed concurrently into the above-mentioned reaction solution containing the first intermediate at feed flow rates of 15 L / h, 100 L / h, and 50 L / h, respectively. A second co-precipitation reaction was carried out at 45 °C and pH=7, with a stirring speed of 250 r / min, to obtain the second intermediate; wherein, the D of the second intermediate... V The particle size of 50 is 12μm.

[0080] S4. The above-mentioned second intermediate is washed with hot water (80°C) to reduce the content of impurity ions to below 100 ppm. The washed material is then fed into a calcining furnace for two calcination treatments. Specifically, the temperature is first increased to 300°C at a rate of 5°C / min and held for 100 min, then increased to 700°C at a rate of 10°C / min and held for 80 min, yielding the following result: Figures 1 to 2 The internally tight and externally loose type of cobalt tetroxide shown is illustrated.

[0081] Example 2 This embodiment provides a cobalt tetroxide with a tight inner structure and a loose outer structure, and a method for preparing the same. The preparation method includes the following steps: S1. Prepare an aluminum-cobalt mixed salt solution with an Al concentration of 1 g / L and a Co concentration of 90 g / L by mixing aluminum chloride and cobalt chloride. Prepare a precipitant solution with a mass concentration of 180 g / L by mixing ammonium bicarbonate and water. Prepare a reaction base solution by mixing the above aluminum-cobalt mixed salt solution with water. The pH value of the reaction base solution is 2.

[0082] The cobalt-aluminum mixed salt solution and the precipitant solution were fed concurrently into the reaction substrate at feed rates of 50 L / h and 50 L / h, respectively. The first co-precipitation reaction nucleation stage was carried out for 1 hour at 50°C and pH=5, with a stirring speed of 100 r / min, yielding a reaction solution containing seed crystals; wherein, the D of the seed crystals... V 50 particles have a diameter of 0.5 μm.

[0083] S2. A cobalt-aluminum mixed salt solution with an Al concentration of 1 g / L and a Co concentration of 90 g / L, and an ammonium bicarbonate precipitant solution with a mass concentration of 180 g / L, were fed concurrently into the above-mentioned reaction solution containing seed crystals at feed flow rates of 20 L / h and 60 L / h, respectively. The first co-precipitation reaction growth stage was carried out for 100 h at 30 °C and pH = 7.5, with a stirring speed of 220 r / min, to obtain a reaction solution containing the first intermediate; wherein, the first intermediate D... V 50 particles have a diameter of 9 μm.

[0084] S3. Prepare a salt solution containing doped elements by mixing nickel chloride and niobium chloride, with a Ni concentration of 0.5 g / L and a Nb concentration of 1 g / L.

[0085] The above-mentioned salt solution containing doped elements, a cobalt-aluminum mixed salt solution with an Al concentration of 1 g / L and a Co concentration of 90 g / L, and an ammonium bicarbonate precipitant solution with a mass concentration of 180 g / L were fed concurrently into the above-mentioned reaction solution containing the first intermediate at feed flow rates of 10 L / h, 120 L / h, and 60 L / h, respectively. A second co-precipitation reaction was carried out at 40 °C and pH = 7.5, with a stirring speed of 200 r / min, to obtain the second intermediate; wherein, the D of the second intermediate... V 50 particles have a diameter of 10 μm.

[0086] S4. The above-mentioned second intermediate is washed with hot water (80°C) at a certain temperature to reduce the content of impurity ions to below 100ppm. Then, the washed material is put into a calcining furnace for two calcination treatments. The specific process includes first heating to 250°C at a heating rate of 1°C / min and holding for 120min, and then heating to 600°C at a heating rate of 5°C / min and holding for 180min to obtain the internally tight and externally loose type of cobalt tetroxide.

[0087] Example 3 This embodiment provides a cobalt tetroxide with a tight inner structure and a loose outer structure, and a method for preparing the same. The preparation method includes the following steps: S1. Prepare an aluminum-cobalt mixed salt solution with an Al concentration of 2.5 g / L and a Co concentration of 100 g / L by mixing aluminum chloride and cobalt chloride. Prepare a precipitant solution with a mass concentration of 200 g / L by mixing ammonium bicarbonate and water. Prepare a reaction base solution by mixing the above aluminum-cobalt mixed salt solution with water. The pH value of the reaction base solution is 7.

[0088] The cobalt-aluminum mixed salt solution and the precipitant solution were fed concurrently into the reaction substrate at feed rates of 70 L / h and 70 L / h, respectively. The first co-precipitation reaction nucleation stage was carried out for 4 hours at 60°C and pH=7, with a stirring speed of 200 r / min, yielding a reaction solution containing seed crystals; wherein, the D of the seed crystals... V 50 particles have a diameter of 1 μm.

[0089] S2. A cobalt-aluminum mixed salt solution with an Al concentration of 2.5 g / L and a Co concentration of 100 g / L, and an ammonium bicarbonate precipitant solution with a mass concentration of 200 g / L, were fed concurrently into the above-mentioned reaction solution containing seed crystals at feed flow rates of 30 L / h and 90 L / h, respectively. The first co-precipitation reaction growth stage was carried out for 100 h at 40 °C and pH=8, with a stirring speed of 250 r / min, to obtain a reaction solution containing the first intermediate; wherein, the first intermediate D... V 50 particles have a diameter of 10 μm.

[0090] S3. Prepare a salt solution containing doped elements by dissolving nickel chloride and niobium chloride in a solution with a Ni concentration of 2.5 g / L and a Nb concentration of 2.5 g / L.

[0091] The above-mentioned salt solution containing doped elements, a cobalt-aluminum mixed salt solution with an Al concentration of 2.5 g / L and a Co concentration of 100 g / L, and an ammonium bicarbonate precipitant solution with a mass concentration of 200 g / L were fed concurrently into the above-mentioned reaction solution containing the first intermediate at feed flow rates of 30 L / h, 150 L / h, and 70 L / h, respectively. A second co-precipitation reaction was carried out at 50 °C and pH=8, with a stirring speed of 250 r / min, to obtain the second intermediate; wherein, the D of the second intermediate... V The particle size of 50 is 11 μm.

[0092] S4. The above-mentioned second intermediate is washed with hot water (80°C) at a certain temperature to reduce the content of impurity ions to below 100ppm. Then, the washed material is put into a calcining furnace for two calcination treatments. The specific process includes first heating to 350°C at a heating rate of 2°C / min and holding for 60min, and then heating to 650°C at a heating rate of 7°C / min and holding for 100min to obtain the internally tight and externally loose type of cobalt tetroxide.

[0093] Example 4 The difference between this embodiment and Embodiment 1 is that the feed flow rate of the cobalt-aluminum mixed salt solution in step S1 is 30 L / h, and the feed flow rate of the second cobalt-aluminum mixed salt solution in step S2 is 20 L / h. All other aspects are the same as in Embodiment 1.

[0094] Example 5 The difference between this embodiment and Embodiment 1 is that, in step S1, the temperature of the nucleation stage of the first coprecipitation reaction is 30°C, while all other aspects are the same as in Embodiment 1.

[0095] Example 6 The difference between this embodiment and Embodiment 1 is that, in step S1, the rotation speed of the nucleation stage of the first coprecipitation reaction is 300 r / min, while all other aspects are the same as in Embodiment 1.

[0096] Example 7 The difference between this embodiment and Embodiment 1 is that, in step S2, the temperature of the growth stage of the first coprecipitation reaction is 50°C, while all other aspects are the same as in Embodiment 1.

[0097] Example 8 The difference between this embodiment and Example 1 is that in step S1, the rotation speed of the growth stage of the first coprecipitation reaction is 150 r / min, while all other aspects are the same as in Example 1.

[0098] Example 9 The difference between this embodiment and Embodiment 1 is that in step S3, the feed flow rate of the cobalt-aluminum mixed salt solution is 90 L / h, while all other aspects are the same as in Embodiment 1.

[0099] Comparative Example 1 The difference between this comparative example and Example 1 is that the feed flow rate of the cobalt-aluminum mixed salt solution in step S1 is 10 L / h, and the feed flow rate of the cobalt-aluminum mixed salt solution in step S2 is 30 L / h. All other aspects are the same as in Example 1.

[0100] Comparative Example 2 The difference between this comparative example and Example 1 is that the type of reaction base solution is adjusted. Specifically, ammonium bicarbonate is mixed with water to prepare a reaction base solution with a mass concentration of 10 g / L. Everything else is the same as in Example 1.

[0101] Comparative Example 3 The difference between this comparative example and Example 1 is that the doping treatment of nickel and niobium in step S3 is not performed. Instead, the first intermediate is directly subjected to the two calcination treatments in step S4 to prepare the precursor. All other aspects are the same as in Example 1.

[0102] Test conditions Lithium cobalt oxide was prepared using the cobalt tetroxide provided in the above examples and comparative examples, and then lithium-ion batteries were fabricated and their performance was tested, as detailed below: The cobalt tetroxide and lithium carbonate provided in the above examples and comparative examples were ball-milled and mixed in a molar ratio of cobalt to lithium of 1:1.02, and then calcined at 900°C for 7 hours to obtain lithium cobalt oxide.

[0103] Preparation of positive electrode sheet: The lithium cobalt oxide positive electrode material, Super P conductive agent and polyvinylidene fluoride binder prepared in the above examples and comparative examples are mixed in a mass ratio of 96:2:2. N-methylpyrrolidone is added and stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry is then coated onto aluminum foil, dried and rolled to obtain a positive electrode sheet.

[0104] Preparation of lithium-ion battery: The above-mentioned positive electrode, separator, electrolyte and lithium metal negative electrode are assembled to obtain CR2032 coin cell, thus obtaining the lithium-ion battery. The electrolyte is prepared by dissolving lithium hexafluorophosphate (LiPF6) in a mixed solvent, which is prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1.

[0105] Electrochemical performance testing: The prepared lithium-ion batteries were subjected to electrochemical performance testing at a test voltage of 3.0V~4.5V. The specific capacity of the lithium-ion batteries during the first discharge at 25℃ and 0.1C rate, the capacity retention rate after 200 charge-discharge cycles, and the discharge capacity retention rate at 3C rate were tested.

[0106] The test results are shown in Table 1.

[0107] Table 1 As can be seen from Table 1, compared with Comparative Examples 1 to 3, the lithium cobalt oxide cathode material (Examples 1 to 3) prepared by the preparation method provided by the present invention with "internal tight and external loose cobalt tetroxide" has a higher initial discharge specific capacity at 0.1C rate, and exhibits better cycle stability (capacity retention rate of more than 95.3% after 200 cycles at room temperature and 0.1C) and high rate performance (discharge capacity retention rate of more than 85.2% at 3C rate).

[0108] In contrast, when the parameters in the preparation process deviated from the preferred range (Examples 4 to 9), the overall electrochemical performance of the prepared lithium cobalt oxide cathode materials all decreased to varying degrees, especially in terms of cycle stability. The materials obtained using the preparation method provided in the comparative examples (Comparative Examples 1 to 3) exhibited the worst electrochemical performance, with not only a lower initial discharge capacity but also significantly lower cycle capacity retention and high-rate performance compared to Examples 1 to 3. This fully demonstrates that the present invention's method of "stage-wise control of reaction conditions" (including using a reaction substrate with a specific composition, controlling the feed flow rate relationship between the salt solution and the precipitant at each stage, and surface doping) to prepare a cobalt tetroxide precursor with a "tight internal and loose external" structure is key to improving the energy density, cycle life, and rate performance of lithium cobalt oxide cathode materials.

[0109] 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 method for preparing cobalt tetroxide with a tight inner structure and a loose outer structure, characterized in that, The preparation method includes the following steps: S1. The first cobalt-aluminum mixed salt solution and the first precipitant solution are fed into the reaction base liquid in parallel to carry out the nucleation stage of the first coprecipitation reaction, and a reaction solution containing seed crystals is obtained. The reaction substrate includes a first cobalt-aluminum mixed salt solution; S2. The second cobalt-aluminum mixed salt solution and the second precipitant solution are fed into the reaction solution containing the seed crystals in parallel to carry out the growth stage of the first co-precipitation reaction, and a reaction solution containing the first intermediate is obtained. S3. The salt solution containing the doped element, the third cobalt-aluminum mixed salt solution, and the third precipitant solution are fed into the reaction solution containing the first intermediate in parallel to carry out a second coprecipitation reaction to obtain the second intermediate; S4. The second intermediate is calcined to obtain the internally compact and externally loose type of cobalt tetroxide; The feed flow rate of the first cobalt-aluminum mixed salt solution is greater than that of the second cobalt-aluminum mixed salt solution, and the feed flow rate of the first precipitant solution is less than that of the second precipitant solution.

2. The production method according to claim 1, characterized by, In step S1, the feed flow rate of the first cobalt-aluminum mixed salt solution is 50 L / h to 70 L / h; Preferably, in step S1, the concentration of cobalt ions in the first cobalt-aluminum mixed salt solution is 90 g / L to 130 g / L; Preferably, in step S1, the concentration of aluminum ions in the first cobalt-aluminum mixed salt solution is 1 g / L to 2.5 g / L; Preferably, in step S1, the feed flow rate of the first precipitant solution is 50 L / h to 70 L / h; Preferably, in step S1, the concentration of the first precipitant solution is 180 g / L to 250 g / L; Preferably, in step S1, the pH of the reaction substrate is 2 to 7.

3. The production method according to claim 1 or 2, characterized by, In step S1, the nucleation stage of the first coprecipitation reaction is carried out under the first stirring, and the stirring speed of the first stirring is 100 r / min to 200 r / min; Preferably, in step S1, the temperature of the nucleation stage of the first coprecipitation reaction is 50℃~60℃; Preferably, in step S1, the pH value of the nucleation stage of the first coprecipitation reaction is 5-7; Preferably, in step S1, the D of the seed crystal V The particle size of 50 particles ranges from 0.5 μm to 2 μm.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step S2, the feed flow rate of the second cobalt-aluminum mixed salt solution is 20 L / h to 30 L / h; Preferably, in step S2, the concentration of cobalt ions in the second cobalt-aluminum mixed salt solution is 90 g / L to 130 g / L; Preferably, in step S2, the concentration of aluminum ions in the second cobalt-aluminum mixed salt solution is 1 g / L to 2.5 g / L; Preferably, in step S2, the feed flow rate of the second precipitant solution is 60 L / h to 90 L / h; Preferably, in step S2, the concentration of the second precipitant solution is 180 g / L to 250 g / L.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step S2, the growth stage of the first coprecipitation reaction is carried out under a second stirring, and the stirring speed of the second stirring is 200 r / min to 250 r / min; Preferably, in step S2, the temperature of the growth stage of the first coprecipitation reaction is 30℃~40℃; Preferably, in step S2, the pH value of the growth stage of the first coprecipitation reaction is 7-8; Preferably, in step S2, the D of the first intermediate V The particle size of 50 particles is 7μm~10μm.

6. The production method according to any one of claims 1 to 5, characterized by, In step S3, the feed flow rate of the salt solution containing the doped element is 10L / h to 30L / h; Preferably, in step S3, the concentration of dopant ions in the salt solution containing dopant elements is 0.5 g / L to 5 g / L; Preferably, the doping element includes any one or a combination of at least two of nickel, magnesium, zirconium, yttrium, or niobium. Preferably, the feed flow rate of the third cobalt-aluminum mixed salt solution is greater than the feed flow rate of the first cobalt-aluminum mixed salt solution; Preferably, in step S3, the feed flow rate of the third cobalt-aluminum mixed salt solution is 100L / h~150L / h; Preferably, in step S3, the concentration of cobalt ions in the third cobalt-aluminum mixed salt solution is 90 g / L to 130 g / L; Preferably, in step S3, the concentration of aluminum ions in the third cobalt-aluminum mixed salt solution is 1 g / L to 2.5 g / L; Preferably, in step S3, the feed flow rate of the third precipitant solution is 50 L / h to 70 L / h; Preferably, in step S3, the concentration of the third precipitant solution is 180 g / L to 250 g / L; Preferably, in step S3, the second coprecipitation reaction is carried out under a third stirring, and the stirring speed of the third stirring is 200 r / min to 250 r / min; Preferably, in step S3, the temperature of the second coprecipitation reaction is 40℃~50℃; Preferably, in step S3, the pH value of the second coprecipitation reaction is 7-8; Preferably, in step S3, the D of the second intermediate V The particle size of 50 particles is 10μm~12μm.

7. The production method according to any one of claims 1 to 6, characterized by, In step S4, the calcination treatment includes a first calcination treatment and a second calcination treatment performed sequentially; Preferably, the temperature of the first calcination treatment is 250℃~350℃, and the time of the first calcination treatment is 60min~120min; Preferably, the heating rate of the first calcination treatment is 1℃ / min to 5℃ / min; Preferably, the temperature of the second calcination treatment is 600℃~700℃, and the time of the second calcination treatment is 30min~180min; Preferably, the heating rate of the second calcination treatment is 5℃ / min to 10℃ / min.

8. An inner-tight outer-loose type of tricobalt tetraoxide, characterized by, The inner-tight and outer-loose type cobalt tetroxide is prepared by the method for preparing the inner-tight and outer-loose type cobalt tetroxide according to any one of claims 1 to 7.

9. A lithium cobaltate characterized by, The lithium cobalt oxide is prepared by calcining cobalt tetroxide (with an inner tight and outer loose structure) with a lithium source according to claim 8.

10. A secondary battery characterized by comprising: The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode includes lithium cobalt oxide as described in claim 9.

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