Doped modified cobaltosic oxide as well as preparation method and application thereof

Abstract

The invention provides doped modified cobaltosic oxide as well as a preparation method and application thereof. The preparation method comprises the following steps: continuously introducing a precipitant solution into a mixed metal salt solution containing a cobalt source and a doped metal source, and carrying out a co-precipitation reaction to prepare a precursor precipitate; and sintering the precursor precipitate to prepare the doped modified cobaltosic oxide. According to the preparation method provided by the invention, the precipitator solution is continuously injected into the mixed metal salt solution containing the cobalt source and the doped metal source, so that the doped metal ions and Co < 2 + > are uniformly coprecipitated at an atomic level, and the doping uniformity is improved; the precipitant solution is injected into the mixed metal salt solution for instantaneous nucleation, the nanoscale precursor with the uniform particle size is generated, and compared with a traditional preparation method that the mixed metal salt solution and the precipitant solution are injected into a base solution in parallel, the size distribution of the material is narrower.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to cathode materials, and more particularly to a doped and modified cobalt tetroxide, its preparation method, and its application. Background Technology

[0002] Ternary cathode materials (such as LiNi) x Co y Mn z O2 or LiNi x Co y Al z O2 (x+y+z=1) is widely used in power batteries due to its high energy density, but its poor interface stability and rapid capacity decay limit its further application. Surface coating is an effective means to improve its performance, and cobalt tetroxide (Co3O4) has become an ideal coating material due to its high electrical conductivity and chemical stability. Metal element doping can further regulate the electronic structure of Co3O4 and enhance its interfacial compatibility with ternary cathode materials.

[0003] CN117185360A discloses a doped cobalt tetroxide, its preparation method, and its application. This invention introduces anions and performs doping; when metal cations are further introduced, they enhance the doping effect with the doped anions. The anions and metal cations are uniformly doped, effectively reducing oxygen evolution in lithium cobalt oxide and improving its structural stability during charge and discharge processes, as well as its cycling stability under high voltage.

[0004] CN108373175A discloses a method for preparing aluminum-doped cobalt tetroxide, comprising the following steps: (1) mixing an aluminum salt solution with a complexing agent to obtain a mixed solution; (2) adding a cobalt salt solution, a precipitant solution containing carbonate ions, and the mixed solution obtained in step (1) into a reaction apparatus in a parallel flow manner to co-precipitate aluminum-doped cobalt carbonate; (3) calcining the aluminum-doped cobalt carbonate obtained in step (2) to obtain aluminum-doped cobalt tetroxide. The aluminum-doped cobalt tetroxide prepared by this invention has a uniform distribution of each element.

[0005] CN112010355A discloses a method for preparing zirconium-doped cobalt tetroxide, comprising mixing a suspension of zirconium oxide with a cobalt salt solution to obtain a mixed solution; adding the mixed solution and a precipitant solution containing carbonate ions in a co-current manner to a reaction apparatus for a co-precipitation reaction to obtain cobalt carbonate encapsulating zirconium oxide; and calcining the cobalt carbonate encapsulating zirconium oxide to obtain cobalt tetroxide. The zirconium-doped cobalt tetroxide prepared by this invention, as a main raw material for lithium cobalt oxide, can improve the rate performance and cycle stability of lithium cobalt oxide under high voltage charge and discharge.

[0006] In existing technologies, metal element doping often relies on complex processes or requires high-temperature, long-duration reactions, resulting in high costs and uneven doping. Therefore, providing a nanoscale cobalt tetroxide with uniform metal element doping is of great significance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a doped and modified cobalt tetroxide, its preparation method, and its applications. In the preparation method provided by the present invention, a precipitant solution is continuously injected into a mixed metal salt solution comprising a cobalt source and a dopant metal source, ensuring the interaction between the dopant metal ions and Co. 2+ Uniform co-precipitation at the atomic level improves doping uniformity; instantaneous nucleation occurs when the precipitant solution is injected into the mixed metal salt solution, generating nanoscale precursors with uniform particle size. Compared with the traditional preparation method of parallel flow of mixed metal salt solution and precipitant solution into the bottom liquid, the size distribution of the material is narrower.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing doped and modified cobalt tetroxide, the method comprising: A precipitant solution is continuously passed into a mixed metal salt solution including a cobalt source and a doped metal source to conduct a co-precipitation reaction and prepare a precursor precipitate; the precursor precipitate is then sintered to prepare the doped modified cobalt tetroxide.

[0009] This invention prepares nanoscale doped and modified cobalt tetroxide based on a coprecipitation-sintering process.

[0010] In the preparation method provided by this invention, a mixed metal salt solution is first prepared by mixing a cobalt source and a doping metal source, providing a foundation for the uniform bulk doping of the doping metal element in cobalt tetroxide. Then, a precipitant solution is continuously injected into the mixed metal salt solution. This direct addition method avoids the component segregation caused by local concentration gradients in traditional co-precipitation processes where the mixed metal salt solution and precipitant solution are flowed concurrently into the base solution, ensuring the uniform doping of the doping metal ions and Co. 2+ Uniform co-precipitation at the atomic level improves doping uniformity; instantaneous nucleation occurs when the precipitant solution is injected into the mixed metal salt solution, generating nanoscale precursors with uniform particle size. Compared with the traditional preparation method of parallel flow of mixed metal salt solution and precipitant solution into the bottom liquid, the size distribution of the material is narrower.

[0011] Preferably, in the mixed metal salt solution, the concentration of cobalt is 100 g / L to 140 g / L, based on the cobalt content in the cobalt source.

[0012] Preferably, in the mixed metal salt solution, the concentration of the dopant metal is 1 g / L to 1.5 g / L, based on the content of the dopant metal in the dopant metal source.

[0013] Preferably, the cobalt source includes any one or a combination of at least two of cobalt chloride, cobalt acetate, or cobalt nitrate.

[0014] Preferably, the doped metal source includes any one or a combination of at least two of aluminum chloride, aluminum nitrate, magnesium chloride, magnesium nitrate, zinc chloride, zinc nitrate, nickel chloride, or nickel nitrate.

[0015] Preferably, the precipitant solution contains any one or a combination of at least two of ammonium carbonate, ammonium bicarbonate, or ammonia water.

[0016] Preferably, the concentration of the precipitant in the precipitant solution is 200 g / L to 260 g / L.

[0017] Preferably, the volume of the mixed metal salt solution is V, and the flow rate of the precipitant solution is 0.8V / min to 2V / min.

[0018] Preferably, the temperature of the coprecipitation reaction is 40℃~50℃.

[0019] Preferably, the precipitant solution is stopped when the co-precipitation reaction reaches a pH of 7.5-8.0.

[0020] Preferably, the coprecipitation reaction is carried out under stirring.

[0021] Preferably, the stirring speed is 500 rpm to 700 rpm.

[0022] Preferably, after washing, NH4 + According to the mass meter, the precursor precipitate still retains ammonium salts with a mass percentage of 3000ppm~4000ppm.

[0023] Preferably, the sintering temperature is 300℃~500℃.

[0024] Preferably, the sintering time is 2h to 4h.

[0025] Preferably, the sintering heating rate is 2℃ / min to 5℃ / min.

[0026] Preferably, the preparation method further includes washing and drying the precursor precipitate.

[0027] Preferably, the sintering atmosphere includes air.

[0028] Secondly, the present invention provides a doped modified cobalt tetroxide, which is prepared by the preparation method described in the first aspect.

[0029] Preferably, the D50 particle size of the doped and modified cobalt tetroxide is 5 nm to 25 nm.

[0030] Preferably, in the doped modified cobalt tetroxide, the doping amount of the doped metal element is 9000ppm~10000ppm.

[0031] Thirdly, the present invention provides a ternary cathode material, the ternary cathode material including a surface coating layer, the material of the surface coating layer including doped and modified cobalt tetroxide as described in the second aspect.

[0032] Fourthly, the present invention provides a lithium-ion battery comprising, as described in the second aspect, doped and modified cobalt tetroxide, or comprising, as described in the third aspect, a ternary cathode material.

[0033] Compared with the prior art, the present invention has the following beneficial effects: In the preparation method provided by this invention, by continuously injecting the precipitant solution into a mixed metal salt solution including a cobalt source and a doped metal source, the interaction between the doped metal ions and Co is ensured. 2+ Uniform co-precipitation at the atomic level improves doping uniformity; instantaneous nucleation occurs when the precipitant solution is injected into the mixed metal salt solution, generating nanoscale precursors with uniform particle size. Compared with the traditional preparation method of parallel flow of mixed metal salt solution and precipitant solution into the bottom liquid, the size distribution of the material is narrower. Attached Figure Description

[0034] Figure 1 This is a SEM image of the doped and modified cobalt tetroxide provided in Example 1 of the present invention.

[0035] Figure 2 This is an EDS diagram of cobalt distribution in doped and modified cobalt tetroxide provided in Example 1 of the present invention.

[0036] Figure 3 This is an EDS diagram of aluminum distribution in doped and modified cobalt tetroxide provided in Example 1 of the present invention. Detailed Implementation

[0037] 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.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having” and any variations thereof in this invention are intended to cover non-exclusive inclusion.

[0039] In the description of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0040] In one specific embodiment, the present invention provides a method for preparing doped and modified cobalt tetroxide, the method comprising: A precipitant solution is continuously passed into a mixed metal salt solution including a cobalt source and a doped metal source to conduct a co-precipitation reaction and prepare a precursor precipitate; the precursor precipitate is then sintered to prepare the doped modified cobalt tetroxide.

[0041] This invention is based on a co-precipitation-sintering process. First, a cobalt source and a doping metal source are mixed to prepare a mixed metal salt solution, providing a foundation for uniform bulk doping of the doping metal element in cobalt tetroxide. Then, a precipitant solution is continuously injected into the mixed metal salt solution. This direct addition method avoids the component segregation caused by local concentration gradients in traditional co-precipitation processes where the mixed metal salt solution and precipitant solution are flowed concurrently into the base solution. This ensures that the doping metal ions and Co are uniformly doped. 2+ Uniform co-precipitation at the atomic level improves doping uniformity; instantaneous nucleation occurs when the precipitant solution is injected into the mixed metal salt solution, generating nanoscale precursors with uniform particle size. Compared with the traditional preparation method of parallel flow of mixed metal salt solution and precipitant solution into the bottom liquid, the size distribution of the material is narrower.

[0042] In some embodiments, the concentration of cobalt in the mixed metal salt solution is 100 g / L to 140 g / L, based on the cobalt content in the cobalt source. For example, it can be 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, 135 g / L, or 140 g / L, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] In some embodiments, the concentration of the dopant metal in the mixed metal salt solution is 1 g / L to 1.5 g / L, based on the content of the dopant metal in the dopant metal source. For example, it can be 1 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L or 1.5 g / L, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In some embodiments, the cobalt source includes any one or a combination of at least two of cobalt chloride, cobalt acetate, or cobalt nitrate. Typical but non-limiting combinations include a combination of cobalt chloride and cobalt acetate, a combination of cobalt nitrate and cobalt chloride, or a combination of cobalt acetate and cobalt nitrate.

[0045] In some embodiments, the doped metal source includes any one or a combination of at least two of aluminum chloride, aluminum nitrate, magnesium chloride, magnesium nitrate, zinc chloride, zinc nitrate, nickel chloride, or nickel nitrate.

[0046] In this invention, the precipitant is preferably a compound containing ammonium ions. After the co-precipitation reaction, the ammonium ions remain on the surface of the precursor precipitate in the form of ammonium salts. The ammonium salts produced serve as sintering aids in the subsequent sintering process, which helps to reduce the sintering temperature and improve the crystallinity of the prepared doped modified cobalt tetroxide.

[0047] In some embodiments, the precipitant solution comprises any one or a combination of at least two of ammonium carbonate, ammonium bicarbonate, or ammonia. Typical but non-limiting combinations include a combination of ammonium carbonate and ammonium bicarbonate, a combination of ammonia and ammonium carbonate, or a combination of ammonium bicarbonate and ammonia.

[0048] In some embodiments, the concentration of the precipitant in the precipitant solution is 200 g / L-260 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 or 260 g / L, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0049] In this invention, a suitable flow rate of the precipitant solution is beneficial for generating nanoscale crystals with uniform dispersion and narrow particle size distribution. If the flow rate is too fast, the crystal nucleation rate will be too fast, and the crystals will easily agglomerate. If the flow rate is too slow, the crystals will grow excessively and become micron-sized particles.

[0050] In some embodiments, with the volume of the mixed metal salt solution as V, the flow rate of the precipitant solution is 0.8V / min to 2V / min, for example, 0.8V / min, 1V / min, 1.2V / min, 1.4V / min, 1.6V / min, 1.8V / min or 2V / min, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0051] In this invention, the coprecipitation temperature affects the uniformity of doping and the crystallinity of the crystal. A suitable coprecipitation temperature is conducive to the formation of a precursor with uniform metal element doping. If the coprecipitation temperature is too low, it will lead to incomplete crystal growth and low crystallinity. If the coprecipitation temperature is too high, it will easily cause segregation of the doped metal element.

[0052] In some embodiments, the temperature of the coprecipitation reaction is 40°C to 50°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C or 50°C, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0053] In this invention, the feeding of the precipitant solution is stopped when the co-precipitation reaction reaches a suitable pH value. If the pH value is too low at the time of stopping the feed, the cobalt content in the supernatant will be high, resulting in a low yield; if the pH value is too high at the time of stopping the feed, the cobalt ions will react with CO3. 2- and OH - Simultaneously, the reaction produces basic cobalt carbonate, which degrades the performance of cobalt tetroxide.

[0054] In some embodiments, the coprecipitation reaction is stopped when the pH reaches 7.5 to 8.0. For example, the pH can be 7.6, 7.5, 7.6, 7.7, 7.8, 7.9, or 8.0, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] In some embodiments, the coprecipitation reaction is carried out under stirring.

[0056] In some embodiments, the stirring speed is 500 rpm to 700 rpm, for example, it can be 500 rpm, 525 rpm, 550 rpm, 575 rpm, 600 rpm, 625 rpm, 650 rpm, 675 rpm or 700 rpm, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] In some embodiments, the preparation method further includes washing and drying the precursor precipitate.

[0058] In some embodiments, after the washing, NH4+ The mass meter indicates that the precursor precipitate still retains ammonium salts with a mass percentage of 3000ppm to 4000ppm. For example, the mass percentage of ammonium salts can be 3000ppm, 3200ppm, 3400ppm, 3600ppm, 3800ppm, or 4000ppm.

[0059] In the preparation method provided by this invention, after the co-precipitation reaction, ammonium ions remain on the surface of the precursor precipitate in the form of ammonium salts. The generated ammonium salts act as sintering aids, helping to lower the sintering temperature and improve the crystallinity of the prepared doped modified cobalt tetroxide. If the sintering temperature is too low, the phase purity is low and the impurity content is high; if the sintering temperature is too high, melting will occur between the grains, leading to an increase in grain size.

[0060] In some embodiments, the sintering temperature is 300°C to 500°C, for example, it can be 300°C, 350°C, 400°C, 450°C or 500°C, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0061] In some embodiments, the sintering time is 2h to 4h, for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0062] In some embodiments, the sintering heating rate is 2℃ / min to 5℃ / min, for example, it can be 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0063] In another specific embodiment, the present invention provides a doped modified cobalt tetroxide, which is prepared by the preparation method described in the first aspect of the foregoing specific embodiment.

[0064] In some embodiments, the D50 particle size of the doped and modified cobalt tetroxide is 5nm to 25nm, for example, it can be 5nm, 10nm, 15nm, 20nm or 25nm, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0065] In some embodiments, the doping amount of the doped metal element in the doped modified cobalt tetroxide is 9000ppm to 10000ppm, for example, it can be 9000ppm, 9200ppm, 9400ppm, 9600ppm, 9800ppm or 10000ppm, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0066] In some embodiments, the sintering atmosphere includes air.

[0067] In yet another specific embodiment, the present invention provides a ternary cathode material, the ternary cathode material including a surface coating layer, the material of the surface coating layer including doped and modified cobalt tetroxide as described in the second aspect of another specific embodiment.

[0068] In a fourth aspect of another specific embodiment, the present invention provides a lithium-ion battery comprising, as described in the second aspect of another specific embodiment, doped and modified cobalt tetroxide, or comprising, as described in the third aspect of yet another specific embodiment, a ternary cathode material.

[0069] Example 1 This embodiment provides a method for preparing doped and modified cobalt tetroxide, the method comprising: Cobalt chloride and aluminum chloride were dissolved in water to prepare a mixed metal salt solution with a cobalt concentration of 120 g / L and an aluminum concentration of 1.15 g / L. 10 L of the mixed metal salt solution was added to a 50 L reactor, followed by the addition of a 220 g / L ammonium bicarbonate solution at a feed rate of 10 L / min until the pH of the reaction system reached 7.8. The ammonium bicarbonate solution was then stopped. The reactor rotation speed was 650 rpm, and the reaction temperature was controlled at 45 °C. The resulting precursor precipitate was centrifuged and washed until the mass percentage of residual ammonium salts was reduced to 3500 ppm. It was then vacuum dried at 80 °C for 12 hours, followed by sintering in air at a rate of 3.5 °C / min to 400 °C for 3 hours. After natural cooling, doped and modified cobalt tetroxide with a D50 particle size of 25 nm was obtained.

[0070] Example 2 This embodiment provides a method for preparing doped and modified cobalt tetroxide, the method comprising: Cobalt nitrate and aluminum nitrate were dissolved in water to prepare a mixed metal salt solution with a cobalt concentration of 100 g / L and an aluminum concentration of 1.02 g / L. 10 L of the mixed metal salt solution was added to a 50 L reactor, followed by the addition of a 260 g / L ammonium carbonate solution at a feed rate of 20 L / min until the pH of the reaction system reached 7.5. The ammonium carbonate solution was then stopped. The reactor rotation speed was 500 rpm, and the reaction temperature was controlled at 40 °C. The resulting precursor precipitate was centrifuged and washed until the mass percentage of residual ammonium salts was reduced to 3000 ppm. It was then vacuum dried at 80 °C for 12 hours, followed by sintering in air at a rate of 2 °C / min to 300 °C for 2 hours, and then allowed to cool naturally to obtain doped modified cobalt tetroxide with a D50 particle size of 20 nm.

[0071] Example 3 This embodiment provides a method for preparing doped and modified cobalt tetroxide, the method comprising: Cobalt nitrate and nickel nitrate were dissolved in water to prepare a mixed metal salt solution with a cobalt concentration of 140 g / L and a nickel concentration of 1.5 g / L. 10 L of the mixed metal salt solution was added to a 50 L reactor, followed by the addition of a 200 g / L ammonia solution at a feed rate of 8 L / min until the pH of the reaction system reached 8.0. The ammonia solution was then stopped. The reactor rotation speed was 700 rpm, and the reaction temperature was controlled at 50 °C. The resulting precursor precipitate was centrifuged and washed until the mass percentage of residual ammonium salts was reduced to 4000 ppm. It was then vacuum dried at 85 °C for 10 hours, followed by sintering in air at a rate of 5 °C / min to 500 °C for 4 hours, and then allowed to cool naturally to obtain doped modified cobalt tetroxide with a D50 particle size of 7 nm.

[0072] Example 4 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that the flow rate of the precipitant solution is 0.6 V / min.

[0073] Example 5 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that the flow rate of the precipitant solution is 2.5 V / min.

[0074] Example 6 This embodiment provides a method for preparing doped modified cobalt tetroxide. Except for the temperature of the coprecipitation reaction being 35°C, the preparation method is the same as in Example 1.

[0075] Example 7 This embodiment provides a method for preparing doped modified cobalt tetroxide. Except for the temperature of the coprecipitation reaction being 55°C, the preparation method is the same as in Example 1.

[0076] Example 8 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that the ammonia bicarbonate solution is stopped when the reaction reaches pH 7.3.

[0077] Example 9 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that the ammonia bicarbonate solution is stopped when the reaction reaches pH 8.2.

[0078] Example 10 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that the sintering temperature is 250°C.

[0079] Example 11 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that the sintering temperature is 550°C.

[0080] Example 12 This embodiment provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that a sodium bicarbonate solution of equal concentration is used instead of an ammonium bicarbonate solution.

[0081] Comparative Example 1 This comparative example provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that 220 g / L of ammonium bicarbonate solution is first added to the reaction vessel, and then a mixed metal salt solution with a cobalt concentration of 120 g / L and an aluminum concentration of 1.15 g / L is added at a feed rate of 10 L / min. The reaction is continued until the pH reaches 7.8 and then the feeding of the mixed metal salt solution is stopped.

[0082] Comparative Example 2 This comparative example provides a method for preparing doped modified cobalt tetroxide. The preparation method is the same as in Example 1, except that a cobalt chloride solution with a cobalt concentration of 120 g / L, an aluminum chloride solution with an aluminum concentration of 1.15 g / L, and an ammonium bicarbonate solution with a concentration of 220 g / L are introduced into the reaction vessel in parallel.

[0083] Performance testing: The doped and modified cobalt tetroxide prepared in Example 1 was subjected to SEM and EDS tests. The test results are shown in [Figure 1]. Figure 1 , Figure 2 and Figure 3 .from Figure 1As shown in the SEM images, the doped and modified cobalt tetroxide prepared in Example 1 are all nano-sized particles with a narrow size distribution. Figure 2 and Figure 3 The EDS test results shown indicate that aluminum is uniformly distributed in the material.

[0084] The doped and modified cobalt tetroxide prepared in all the above examples and comparative examples were ball-milled and mixed with NCM811 cathode at a mass ratio of 30:1 to prepare a uniform coating layer on the surface of NCM811. The NCM811 material before and after coating was then mixed with PVDF and conductive carbon black at a mass ratio of 94:3:3 to prepare a cathode sheet. Using lithium metal as the anode, coin cells were assembled. The 1C discharge specific capacity, 5C discharge specific capacity, and discharge capacity retention rate after 500 1C cycles were tested at 25°C and a voltage range of 3.0-4.3. The test results are shown in Table 1.

[0085] Table 1 In summary, the preparation method provided by this invention ensures that the doped metal ions react with Co by continuously injecting the precipitant solution into a mixed metal salt solution including a cobalt source and a doped metal source. 2+ Uniform co-precipitation at the atomic level improves doping uniformity; instantaneous nucleation occurs when the precipitant solution is injected into the mixed metal salt solution, generating nanoscale precursors with uniform particle size. Compared with the traditional preparation method of parallel flow of mixed metal salt solution and precipitant solution into the bottom liquid, the size distribution of the material is narrower.

[0086] Based on the test results of Example 1, Comparative Example 1, and Comparative Example 2, if the mixing method of continuously injecting the precipitant solution into the mixed metal salt solution in Example 1 is adjusted to passing the mixed metal salt solution into the precipitant solution, or to passing the mixed metal salt solution and the precipitant solution into the reactor in parallel, it is impossible to prepare a nanoscale precursor with uniform particle size. Furthermore, the coating modification effect of the doped and modified cobalt tetroxide on the NCM811 cathode is also not ideal, and the rate performance and cycle performance both show a significant decrease.

[0087] According to the test results of Examples 1, 4 and 5, if the feeding rate of the precipitant solution is too slow, it cannot nucleate rapidly and instantaneously, and the crystals grow excessively into micron-sized particles; if the feeding rate of the precipitant solution is too fast, it will cause the crystal nucleation rate to be too fast, and the crystals will easily agglomerate.

[0088] Based on the test results of Examples 1, 6, and 7, if the co-precipitation temperature is too low, it will lead to incomplete crystal growth and low crystallinity; if the co-precipitation temperature is too high, it will easily cause segregation of doped metal elements.

[0089] Based on the test results of Examples 1, 8, and 9, if the pH is too low at the time of stopping the feed, the cobalt content in the supernatant will be high, resulting in a low yield; if the pH is too high at the time of stopping the feed, cobalt ions will react with CO3. 2- and OH - Simultaneously, the reaction produces basic cobalt carbonate, which degrades the performance of cobalt tetroxide.

[0090] According to the test results of Examples 1, 10 and 11, if the sintering temperature is too low, the purity of the precursor phase is low and the impurity content is high; if the sintering temperature is too high, melting will occur between the grains, resulting in an increase in particle size, and it will be impossible to prepare nanoscale doped modified cobalt tetroxide.

[0091] According to the test results of Examples 1 and 12, if the ammonium bicarbonate solution is replaced with a sodium bicarbonate solution that does not contain ammonium ions, ammonium salts cannot remain on the surface of the precursor precipitate, thus improving the crystallinity of the prepared doped modified cobalt tetroxide at a lower sintering temperature.

[0092] 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 doped and modified cobalt tetroxide, characterized in that, The preparation method includes: A precipitant solution is continuously passed into a mixed metal salt solution including a cobalt source and a doped metal source to conduct a co-precipitation reaction and prepare a precursor precipitate; the precursor precipitate is then sintered to prepare the doped modified cobalt tetroxide.

2. The preparation method according to claim 1, characterized in that, In the mixed metal salt solution, the concentration of cobalt is 100 g / L to 140 g / L, based on the cobalt content in the cobalt source. And / or, in the mixed metal salt solution, the concentration of the doped metal is 1 g / L to 1.5 g / L, based on the content of the doped metal in the doped metal source.

3. The preparation method according to claim 1 or 2, characterized in that, The precipitant solution contains any one or a combination of at least two of ammonium carbonate, ammonium bicarbonate, or ammonia water. And / or, the concentration of the precipitant in the precipitant solution is 200 g / L-260 g / L.

4. The preparation method according to any one of claims 1 to 3, characterized in that, With the volume of the mixed metal salt solution as V, the flow rate of the precipitant solution is 0.8V / min to 2V / min.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The temperature of the coprecipitation reaction is 40℃~50℃; And / or, when the coprecipitation reaction reaches a pH of 7.5-8.0, the flow of the precipitant solution is stopped; And / or, the coprecipitation reaction is carried out under stirring.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The sintering atmosphere includes air; And / or, the sintering temperature is 300℃~500℃; And / or, the sintering time is 2h~4h; And / or, the sintering heating rate is 2℃ / min to 5℃ / min.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The preparation method further includes washing and drying the precursor precipitate.

8. A doped and modified cobalt tetroxide, characterized in that, The doped and modified cobalt tetroxide is prepared by the preparation method according to any one of claims 1 to 7.

9. A ternary cathode material, characterized in that, The ternary cathode material includes a surface coating layer, and the material of the surface coating layer includes the doped and modified cobalt tetroxide as described in claim 8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the doped and modified cobalt tetroxide as described in claim 8, or the ternary cathode material as described in claim 9.

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