Coated modified lithium cobalt oxide material, preparation method thereof, positive electrode and lithium ion battery

Abstract

This invention provides a coated and modified lithium cobalt oxide material, its preparation method, a cathode, and a lithium-ion battery. The preparation method includes: providing a mixture comprising, from bottom to top, first lithium cobalt oxide particles, a coating agent, and second lithium cobalt oxide particles; sequentially performing a first mixing, a second mixing, and a third mixing on the mixture; and sintering to obtain the coated and modified lithium cobalt oxide material; wherein the D50 particle size of the first lithium cobalt oxide particles is larger than that of the second lithium cobalt oxide particles; and the mixing speeds of the first, second, and third mixing processes increase sequentially. In the process of coating and modifying lithium cobalt oxide, this invention designs the vertical positions of the first and second lithium cobalt oxide particles and the coating agent in the mixture to form a "sandwich" structure. Combined with a three-stage mixing process, this significantly improves the uniformity of the mixing of the coating agent and the lithium cobalt oxide material, achieving uniform coating of the coating elements on the surface of the lithium cobalt oxide material.

Description

Technical Field

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

[0002] With the continuous development of technology and the increasing demands on 3C and other electronic products, the development of lithium cobalt oxide cathode materials suitable for high voltage applications is urgently needed. Currently, the actual specific capacity of lithium cobalt oxide cathode materials is 170mAh / g-190mAh / g, far lower than its theoretical specific capacity of 274mAh / g. Furthermore, when used at voltages of 4.4V and above, structural collapse is highly likely to occur, leading to irreversible energy loss and thus affecting its service life.

[0003] To address the aforementioned issues, a common improvement approach in the prior art is to coat the surface of lithium cobalt oxide materials with high-entropy metal elements to stabilize the structure. However, the precise control of the amount of coating elements and the uniformity of the coating both affect the performance of the coated lithium cobalt oxide materials.

[0004] CN103151518A discloses a coating process for lithium cobalt oxide. By adding water-soluble organic matter during the coating process, the components can be kept uniform and stable during the subsequent drying and calcination of lithium cobalt oxide. This avoids the segregation of metal ion compounds at high temperatures, prevents element precipitation, and ensures the electrical performance of the coated lithium cobalt oxide. This effectively solves the problem that the electrical performance of lithium cobalt oxide is affected after high-temperature calcination. Furthermore, the process employs a high-speed, short-time ball milling of the slurry in the first stage and a low-speed, long-time ball milling of the slurry in the second stage to ensure that the metal ion compounds, water-soluble organic matter, and lithium cobalt oxide are fully and uniformly mixed, and the particle size is finer and more uniform, which is beneficial to improving the uniformity of coating and the electrical performance of the product.

[0005] CN102842712A discloses a method for preparing coated lithium cobalt oxide cathode material. The method includes feeding primary graded lithium cobalt oxide into a pressure cooker containing coating material and deionized water. Under certain pressure and temperature, the mixture is continuously stirred until fully mixed and homogeneous, then the pressure is released and the material is discharged. The material is then dried at low temperature and sieved, followed by high-temperature solid-phase sintering. Finally, it is mechanically pulverized, graded, and cooled to obtain the finished product. This invention combines high-temperature solid-phase and pressure-cooked liquid-phase methods to accelerate the microscopic movement of particles under certain temperature and pressure conditions, allowing for thorough mixing and penetration of the material, thus preparing a uniformly coated lithium cobalt oxide cathode material with excellent electrochemical performance.

[0006] CN117882212A discloses a method for preparing coated modified lithium cobalt oxide, comprising spraying a solution containing the sodium salt onto a substrate and drying the sodium salt on the substrate until the sodium salt on the substrate surface reaches a specified thickness or mass to obtain pre-coated particles; then mixing the pre-coated particles with a gel of raw material containing a composite coating layer, and then calcining to obtain the coated modified lithium cobalt oxide.

[0007] Existing methods for improving the uniformity of lithium cobalt oxide coating all require solution or sol-gel methods, which are complex to prepare. Furthermore, lithium cobalt oxide materials are sensitive to water, so a strict drying process is required to meet the application requirements.

[0008] Therefore, there is an urgent need to provide a method for preparing coated modified lithium cobalt oxide materials that can precisely control the coating amount, improve coating uniformity, and is suitable for industrial production. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a coated and modified lithium cobalt oxide material, its preparation method, a cathode, and a lithium-ion battery. In the process of coating and modifying lithium cobalt oxide, the present invention designs the vertical positions of the first lithium cobalt oxide particles, the second lithium cobalt oxide particles, and the coating agent in the mixture. The larger first lithium cobalt oxide particles are placed at the bottom layer, the smaller second lithium cobalt oxide particles are placed at the top layer, and the coating agent is placed between the first and second lithium cobalt oxide particles, forming a "sandwich" structure. Combined with a three-stage mixing process, this significantly improves the uniformity of the mixing between the coating agent and the lithium cobalt oxide material, achieving uniform coating of the coating elements on the surface of the lithium cobalt oxide material.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a method for coating the surface of a modified lithium cobalt oxide material, the preparation method comprising:

[0012] A mixture is provided, comprising, from bottom to top, first lithium cobalt oxide particles, a coating agent, and second lithium cobalt oxide particles; the mixture is subjected to a first mixing, a second mixing, and a third mixing in sequence; sintering is performed to obtain the coated modified lithium cobalt oxide material; the D50 particle size of the first lithium cobalt oxide particles is larger than that of the second lithium cobalt oxide particles; the mixing speeds of the first mixing, the second mixing, and the third mixing increase sequentially.

[0013] In the process of lithium cobalt oxide coating modification, this invention designs the vertical positions of the first lithium cobalt oxide particles, the second lithium cobalt oxide particles, and the coating agent in the mixture. The larger first lithium cobalt oxide particles are placed at the bottom, the smaller second lithium cobalt oxide particles at the top, and the coating agent is placed between the first and second lithium cobalt oxide particles, forming a "sandwich" structure. This effectively prevents the coating agent from being lost due to powder flying or adhering to the walls during mixing, avoiding deviations in the coating amount and achieving precise control of the coating amount. Furthermore, placing the larger first lithium cobalt oxide particles at the bottom and the smaller second lithium cobalt oxide particles at the top facilitates uniform mixing of the two particles. Combined with a three-stage process... The mixing process begins with a low mixing speed at the initial stage to initially mix the coating agent with the first and second lithium cobalt oxide particles. During this process, the larger lithium cobalt oxide particles collide with the smaller ones, causing the coating agent to be adsorbed onto the surfaces of the first and second lithium cobalt oxide particles. Then, the mixing speed is increased for a second mixing process, preventing powder from flying off the coating agent. After the second mixing, the coating agent is uniformly coated on the surface of the lithium cobalt oxide. A third mixing process, with a further increase in the mixing speed, achieves a uniform and dense coating of the coating agent on the surfaces of both the first and second lithium cobalt oxide particles, while simultaneously achieving uniform mixing of the two particles.

[0014] Preferably, the D50 particle size of the first lithium cobalt oxide particles is 15μm~30μm, and more preferably 16μm~20μm.

[0015] Preferably, the D50 particle size of the second lithium cobalt oxide particles is 1μm to 10μm, and more preferably 3μm to 6μm.

[0016] Preferably, the mass ratio of the first lithium cobalt oxide particle to the second lithium cobalt oxide particle is (3~5):1.

[0017] Preferably, the mass of the coating agent is 0.01wt% to 7wt% of the total mass of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles.

[0018] Preferably, the coating agent comprises any one or a combination of at least two of cobalt hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, yttrium oxide, or lanthanum oxide.

[0019] Preferably, the first lithium cobalt oxide particle and the second lithium cobalt oxide particle each independently include 0.4wt% to 1wt% of the doping element Al.

[0020] Preferably, the mixing speed of the first mixture is 70 rpm to 220 rpm.

[0021] Preferably, the mixing speed of the second mixture is 280 rpm to 420 rpm.

[0022] Preferably, the mixing speed of the third mixture is 480 rpm to 640 rpm.

[0023] Preferably, the first mixing time is 3 min to 10 min.

[0024] Preferably, the second mixing time is 5 min to 20 min.

[0025] Preferably, the third mixing time is 2 min to 8 min.

[0026] Preferably, the sintering temperature is 750℃~1000℃.

[0027] Preferably, the sintering time is 15h to 20h.

[0028] In a second aspect, the present invention provides a coated modified lithium cobalt oxide material, wherein the coated modified lithium cobalt oxide material is coated by the coating method described in the first aspect.

[0029] The coated modified lithium cobalt oxide material provided by this invention has a coating layer with uniform thickness and uniform element distribution on its surface, exhibiting stable structure and good cycle performance.

[0030] Thirdly, the present invention provides a positive electrode comprising a coated modified lithium cobalt oxide material as described in the second aspect.

[0031] Fourthly, the present invention provides a lithium-ion battery comprising a coated modified lithium cobalt oxide material as described in the second aspect, or a positive electrode as described in the third aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] In the process of coating and modifying lithium cobalt oxide, this invention designs the vertical positions of the first lithium cobalt oxide particles, the second lithium cobalt oxide particles, and the coating agent in the mixture. The larger first lithium cobalt oxide particles are placed at the bottom layer, the smaller second lithium cobalt oxide particles are placed at the top layer, and the coating agent is placed between the first and second lithium cobalt oxide particles to form a "sandwich" structure. Combined with a three-stage mixing process, this significantly improves the uniformity of the mixing between the coating agent and the lithium cobalt oxide material, and achieves uniform coating of the coating elements on the surface of the lithium cobalt oxide material. Attached Figure Description

[0034] Figure 1 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Example 1.

[0035] Figure 2 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Example 4.

[0036] Figure 3 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Example 5.

[0037] Figure 4 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Comparative Example 1.

[0038] Figure 5 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Comparative Example 2.

[0039] Figure 6 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Comparative Example 3.

[0040] Figure 7 This is an EDS image of the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Comparative Example 4. Detailed Implementation

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In a first specific embodiment, the present invention provides a method for coating the surface of a modified lithium cobalt oxide material, the preparation method comprising:

[0045] A mixture is provided, comprising, from bottom to top, first lithium cobalt oxide particles, a coating agent, and second lithium cobalt oxide particles; the mixture is subjected to a first mixing, a second mixing, and a third mixing in sequence; sintering is performed to obtain the coated modified lithium cobalt oxide material; the D50 particle size of the first lithium cobalt oxide particles is larger than that of the second lithium cobalt oxide particles; the mixing speeds of the first mixing, the second mixing, and the third mixing increase sequentially.

[0046] In the process of lithium cobalt oxide coating modification, this invention designs the vertical positions of the first lithium cobalt oxide particles, the second lithium cobalt oxide particles, and the coating agent in the mixture. The larger first lithium cobalt oxide particles are placed at the bottom, the smaller second lithium cobalt oxide particles at the top, and the coating agent is placed between the first and second lithium cobalt oxide particles, forming a "sandwich" structure. This effectively prevents the coating agent from being lost due to powder flying or adhering to the walls during mixing, avoiding deviations in the coating amount and achieving precise control of the coating amount. Furthermore, placing the larger first lithium cobalt oxide particles at the bottom and the smaller second lithium cobalt oxide particles at the top facilitates uniform mixing of the two particles. Combined with a three-stage process... The mixing process begins with a low mixing speed at the initial stage to initially mix the coating agent with the first and second lithium cobalt oxide particles. During this process, the larger lithium cobalt oxide particles collide with the smaller ones, causing the coating agent to be adsorbed onto the surfaces of the first and second lithium cobalt oxide particles. Then, the mixing speed is increased for a second mixing process, preventing powder from flying off the coating agent. After the second mixing, the coating agent is uniformly coated on the surface of the lithium cobalt oxide. A third mixing process, with a further increase in the mixing speed, achieves a uniform and dense coating of the coating agent on the surfaces of both the first and second lithium cobalt oxide particles, while simultaneously achieving uniform mixing of the two particles.

[0047] In some embodiments, the D50 particle size of the first lithium cobalt oxide particle is 15μm to 30μm, for example, it can be 15μm, 17μm, 19μm, 21μm, 23μm, 25μm, 27μm, 29μm or 30μm, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 16μm to 20μm.

[0048] In some embodiments, the D50 particle size of the second lithium cobalt oxide particle is 1μm to 10μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 3μm to 6μm.

[0049] In some embodiments, the mass ratio of the first lithium cobalt oxide particle to the second lithium cobalt oxide particle is (3~5):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0050] In some embodiments, the mass of the coating agent is 0.01wt% to 7wt% of the total mass of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles. For example, it can be 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, or 7wt%, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] In some embodiments, the coating agent comprises any one or a combination of at least two of cobalt hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, yttrium oxide, or lanthanum oxide. Typical but non-limiting combinations include a combination of cobalt hydroxide and magnesium oxide, a combination of titanium dioxide and zirconium oxide, or a combination of yttrium oxide and lanthanum oxide.

[0052] In some embodiments, the first lithium cobalt oxide particle and the second lithium cobalt oxide particle each independently include 0.4wt% to 1wt% of the doping element Al. For example, the doping amount of Al can be 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%, including but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] In this invention, the first mixing is performed at a relatively slow speed to avoid dust generation and particle agglomeration, preventing particle flying and dust generation, thus reducing material loss. It also avoids agglomeration of the coating agent due to airflow disturbance. However, if the mixing speed of the first mixing is too low, the material cannot flow sufficiently, which is detrimental to the uniformity of mixing; if the mixing speed of the first mixing is too high, dust will be generated, causing material loss and reducing the mixing effect, and the coating amount cannot be accurately controlled.

[0054] In some embodiments, the mixing speed of the first mixture is 70 rpm to 220 rpm, for example, it can be 70 rpm, 90 rpm, 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm, 200 rpm or 220 rpm, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0055] In this invention, the second mixing drives the powder to form an overall flow, and macroscopic uniformity is achieved through tumbling and convection. Appropriate shear force can break up the soft agglomerates of additives that were not fully dispersed in the first mixing stage. If the mixing speed of the second mixing is too low, it will not be able to fully break up the soft agglomerates in the first mixing stage. If the mixing speed of the second mixing is too high, excessive friction between particles will lead to an increase in temperature and cause certain damage to the lithium cobalt oxide particles.

[0056] In some embodiments, the mixing speed of the second mixture is 280 rpm to 420 rpm, for example, it can be 280 rpm, 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm or 420 rpm, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] In this invention, strong turbulence and shear force are generated during the third mixing process, which thoroughly disperses micro- and nano-sized agglomerates, ensuring microscopic uniformity and coating the particle surface. If the mixing speed of the third mixing is too low, the coating effect will be poor and the mixing effect will not be achieved. If the mixing speed of the third mixing is too high, excessive friction may cause significant damage to the surface of lithium cobalt oxide particles, and the generated high temperature will cause the reaction between additives to start prematurely, affecting the final coating effect.

[0058] In some embodiments, the mixing speed of the third mixture is 480 rpm to 640 rpm, for example, it can be 480 rpm, 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm, 600 rpm, 620 rpm or 640 rpm, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0059] In some implementations, the first mixing time is 3 min to 10 min, for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0060] In some embodiments, the second mixing time is 5 min to 20 min, for example, it can be 5 min, 7 min, 9 min, 11 min, 13 min, 15 min, 17 min, 19 min or 20 min, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0061] In some embodiments, the third mixing time is 2 min to 8 min, for example, it can be 2 min, 3 min, 4 min, 5 min, 6 min, 7 min or 8 min, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0062] In some embodiments, the sintering temperature is 750°C to 1000°C, for example, it can be 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0063] In some embodiments, the sintering time is 15h to 20h, for example, it can be 15h, 16h, 17h, 18h, 19h or 20h, including but not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0064] In another specific embodiment, the present invention provides a coated modified lithium cobalt oxide material, wherein the coated modified lithium cobalt oxide material is coated by the coating method described in the foregoing specific embodiment.

[0065] The coated modified lithium cobalt oxide material provided by this invention has a coating layer with uniform thickness and uniform element distribution on its surface, exhibiting stable structure and good cycle performance.

[0066] In yet another embodiment, the present invention provides a positive electrode comprising a coated modified lithium cobalt oxide material as described in another preceding embodiment.

[0067] In another specific embodiment, the present invention provides a lithium-ion battery comprising a coated modified lithium cobalt oxide material as described in another specific embodiment above, or comprising a positive electrode as described in yet another specific embodiment above.

[0068] Example 1

[0069] This embodiment provides a method for coating the surface of a modified lithium cobalt oxide material, the preparation method comprising:

[0070] (1) Add first lithium cobalt oxide particles with a D50 particle size of 18 μm, zirconium oxide and second lithium cobalt oxide particles with a D50 particle size of 5 μm to the mixer in sequence; the mass ratio of the first lithium cobalt oxide particles to the second lithium cobalt oxide particles is 4:1, the doping amount of Al in the first lithium cobalt oxide particles is 0.6 wt%, the doping amount of Al in the second lithium cobalt oxide particles is 0.8 wt% of doping element Al, and the mass of zirconium oxide is 1 wt% of the total mass of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles.

[0071] (2) Perform the first mixing at a speed of 120 rpm for 5 min, the second mixing at a speed of 350 rpm for 10 min, and the third mixing at a speed of 560 rpm for 5 min in sequence;

[0072] (3) The mixed material is sintered at 850°C for 18 hours in an air atmosphere to obtain the coated modified lithium cobalt oxide material.

[0073] Example 2

[0074] This embodiment provides a method for coating the surface of a modified lithium cobalt oxide material, the preparation method comprising:

[0075] (1) First lithium cobalt oxide particles with a D50 particle size of 16 μm, magnesium oxide and second lithium cobalt oxide particles with a D50 particle size of 3 μm are added sequentially to the mixer; the mass ratio of the first lithium cobalt oxide particles to the second lithium cobalt oxide particles is 3:1, the doping amount of Al in the first lithium cobalt oxide particles is 0.4 wt%, the doping amount of Al in the second lithium cobalt oxide particles is 0.5 wt% of the doping element Al, and the mass of the magnesium oxide is 0.01 wt% of the total mass of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles.

[0076] (2) Perform the first mixing at a speed of 70 rpm for 3 min, the second mixing at a speed of 280 rpm for 5 min, and the third mixing at a speed of 480 rpm for 2 min in sequence;

[0077] (3) The mixed material is sintered at 750°C for 15 hours in an air atmosphere to obtain the coated modified lithium cobalt oxide material.

[0078] Example 3

[0079] This embodiment provides a method for coating the surface of a modified lithium cobalt oxide material, including:

[0080] (1) Add first lithium cobalt oxide particles with a D50 particle size of 20 μm, titanium dioxide and second lithium cobalt oxide particles with a D50 particle size of 6 μm to the mixer in sequence; the mass ratio of the first lithium cobalt oxide particles to the second lithium cobalt oxide particles is 5:1, the doping amount of Al in the first lithium cobalt oxide particles is 1 wt%, the doping amount of Al in the second lithium cobalt oxide particles is 0.8 wt% of doping element Al, and the mass of the titanium dioxide is 7 wt% of the total mass of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles.

[0081] (2) Perform the first mixing at a speed of 220 rpm for 10 min, the second mixing at a speed of 420 rpm for 20 min, and the third mixing at a speed of 640 rpm for 8 min in sequence;

[0082] (3) The mixed material is sintered at 1000°C for 20 hours in an air atmosphere to obtain the coated modified lithium cobalt oxide material.

[0083] Example 4

[0084] This embodiment provides a method for coating the surface of modified lithium cobalt oxide material. Except for the mixing speed of the first mixing step (2) being 250 rpm, the preparation method is the same as in Example 1.

[0085] Example 5

[0086] This embodiment provides a method for coating the surface of modified lithium cobalt oxide material. Except for the mixing speed of the third mixing step (2) being 400 rpm, the preparation method is the same as in Example 1.

[0087] Comparative Example 1

[0088] This comparative example provides a method for coating the surface of a modified lithium cobalt oxide material. Except for step (1), in which the first lithium cobalt oxide particles and the second lithium cobalt oxide particles are simultaneously added to a mixer and then zirconium oxide is added, the preparation method is the same as in Example 1.

[0089] Comparative Example 2

[0090] This comparative example provides a method for coating the surface of a modified lithium cobalt oxide material. The preparation method is the same as that in Example 1, except that step (2) does not involve the first mixing.

[0091] Comparative Example 3

[0092] This comparative example provides a method for coating the surface of a modified lithium cobalt oxide material. The preparation method is the same as that of Comparative Example 2, except that the mixing time in step (2) is increased to 12 min.

[0093] Comparative Example 4

[0094] This comparative example provides a method for coating the surface of a modified lithium cobalt oxide material. Except for step (2), which involves mixing at a speed of 250 rpm for 10 min and mixing at a speed of 380 rpm for 20 min, the preparation method is the same as in Example 1.

[0095] Performance testing:

[0096] The cycle capacity retention of the coated modified lithium cobalt oxide materials prepared in all the above embodiments and comparative examples was tested under the following conditions:

[0097] A positive electrode was prepared by coating modified lithium cobalt oxide material with conductive carbon black and PVDF at a mass ratio of 8:1:1. A coin cell was prepared using lithium metal as the negative electrode. The cells were charged and discharged at 45°C at 1C, and the capacity retention rate was tested after 50 cycles. The test results are shown in Table 1.

[0098] Table 1

[0099]

[0100] EDS tests were performed on the coated and modified lithium cobalt oxide materials prepared in Examples 1, 4, 5, and all comparative examples. The test results are shown in [Figure number missing]. Figures 1 to 7 .like Figure 1 As shown, the Zr element on the surface of the coated modified lithium cobalt oxide material prepared in Example 1 is uniformly distributed with no obvious enrichment areas.

[0101] like Figure 2 and Figure 3 As shown, if the rotation speed of the first mixture is too fast, or the rotation speed of the third mixture is too slow, the uniformity of Zr element distribution deteriorates, and a slight enrichment phenomenon occurs.

[0102] like Figure 4 As shown, if the "sandwich feeding" method of this invention is not used, but the first and second lithium cobalt oxide particles are directly added to the mixer, multiple small-scale Zr element aggregation areas appear on the surface of the prepared coated modified lithium cobalt oxide material. Figure 5 As shown, if the first mixing is skipped and the second and third mixing are performed directly, the coating agent will not be able to mix sufficiently and evenly with the first and second lithium cobalt oxide particles, resulting in Zr enrichment regions on the surface of the lithium cobalt oxide material. Even if the third mixing time is extended to 12 minutes, as... Figure 6 As shown, Zr enrichment regions still exist. Figure 7 As shown, according to the conventional two-stage mixing process, the mixing speed of the first stage is higher than that of the first mixing in this invention, and the mixing speed of the second stage is lower than that of the third mixing in this invention. Although the total mixing time is as long as 30 minutes, the uniformity of Zr element distribution on the surface of the prepared coated modified lithium cobalt oxide material is poor, and there are many Zr element enrichment areas.

[0103] 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 a coated and modified lithium cobalt oxide material, characterized in that, The preparation method includes: A mixture is provided, comprising, from bottom to top, first lithium cobalt oxide particles, a coating agent, and second lithium cobalt oxide particles; the mixture is subjected to a first mixing, a second mixing, and a third mixing in sequence; and sintered to obtain the coated and modified lithium cobalt oxide material. The D50 particle size of the first lithium cobalt oxide particle is larger than that of the second lithium cobalt oxide particle. The mixing speed of the first mixture is 70 rpm to 220 rpm; the mixing speed of the second mixture is 280 rpm to 420 rpm; and the mixing speed of the third mixture is 480 rpm to 640 rpm. The first mixing time is 3 min to 10 min; the second mixing time is 5 min to 20 min; and the third mixing time is 2 min to 8 min.

2. The preparation method according to claim 1, characterized in that, The D50 particle size of the first lithium cobalt oxide particle is 15μm~30μm; And / or, the D50 particle size of the second lithium cobalt oxide particles is 1 μm to 10 μm.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the first lithium cobalt oxide particle to the second lithium cobalt oxide particle is (3~5):1; And / or, the mass of the coating agent is 0.01wt% to 7wt% of the total mass of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles.

4. The preparation method according to claim 1, characterized in that, The coating agent includes any one or a combination of at least two of cobalt hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, yttrium oxide, or lanthanum oxide; And / or, the first lithium cobalt oxide particle and the second lithium cobalt oxide particle each independently include 0.4wt% to 1wt% of the doping element Al.

5. The preparation method according to claim 1, characterized in that, The sintering temperature is 750℃~1000℃; And / or, the sintering time is 15h~20h.

6. A coated and modified lithium cobalt oxide material, characterized in that, The coated and modified lithium cobalt oxide material is prepared by the preparation method described in any one of claims 1 to 5.

7. A positive electrode, characterized in that, The positive electrode comprises the coated modified lithium cobalt oxide material as described in claim 6.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the coated modified lithium cobalt oxide material as described in claim 6, or includes the positive electrode as described in claim 7.

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