A lithium cobalt oxide positive electrode material and its preparation method and application

Abstract

The present invention provides a lithium cobalt oxide positive electrode material and a preparation method and application thereof; the preparation method comprises the following steps: a) mixing a cobalt source A, a lithium source C and a doping element D, performing a first sintering, and mechanically crushing to obtain a matrix lithium cobalt oxide; b) mixing a cobalt source B, a lithium source C and a doping element E, performing a second sintering, and airflow crushing to obtain a primary lithium cobalt oxide; c) mixing the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and an additive, performing a third sintering, and mechanically crushing to obtain a single-sintered product having a core-shell structure; d) mixing the single-sintered product having a core-shell structure obtained in step c) with a coating agent, performing a fourth sintering, and depolymerizing to obtain a lithium cobalt oxide positive electrode material; there is no order restriction for steps a) and b). The preparation method uses doping and coating means to improve the performance of the lithium cobalt oxide positive electrode material, and can prepare a lithium cobalt oxide positive electrode material with high safety of more than 4.5V.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode materials, and more specifically, to a lithium cobalt oxide positive electrode material and a preparation method and application thereof. Background Art

[0002] In the field of portable electronic devices, lithium cobalt oxide still dominates the cathode material market. In order to pursue higher energy density, it is necessary to increase the charging voltage of lithium cobalt oxide batteries. During the charging and discharging process of lithium cobalt oxide materials, Li + A large amount of extraction and insertion of lithium cobalt oxide materials + After that, the bulk and surface structure of the material will become extremely unstable, leading to irreversible phase change. In addition, the extremely unstable structure of the lithium cobalt oxide surface will also cause a series of side reactions with the electrolyte. At the same time, the surface of the material is also accompanied by oxygen evolution and cobalt dissolution, resulting in a decrease in battery performance, rapid capacity decay, and safety accidents. All of these seriously hinder the application of lithium cobalt oxide materials under high voltage. It is worth noting that as the charge and discharge voltage increases, the material's Li desorption rate increases. + As the amount of lithium cobalt increases, the above problems become more serious. Studies have found that the main reasons for the failure of high-voltage lithium cobalt oxide positive electrode materials come from two aspects: (1) irreversible structural phase change and (2) surface side reactions. The former can be slowed down by doping modification technology, and the latter can be stabilized by coating to stabilize the surface structure and inhibit surface side reactions. With the deepening of understanding of doping and coating technology, the application voltage of lithium cobalt oxide has been continuously increased from the initial 4.2V to 4.5V. The higher the application voltage, the more significantly the battery capacity, voltage platform and energy density will be improved, but the material will also face many problems, which will become more serious as the voltage increases. However, it is difficult to achieve the application of lithium cobalt oxide at voltages above 4.5V using the current doping and coating technology.

[0003] In summary, phase change, side reaction, oxygen evolution and cobalt dissolution have become the biggest challenges for the application of high-voltage lithium cobalt oxide. However, in order to achieve the application of lithium cobalt oxide above 4.5V, it is necessary to take into account structural reversibility, interface stability and thermal stability. As we all know, doping and coating are the most commonly used technical improvement solutions for high-voltage lithium cobalt oxide. Element doping can stabilize the structure of the material, inhibit irreversible phase change, and also have the effects of improving material conductivity and ion diffusion. Generally speaking, the effect of doping elements in stabilizing the structure is proportional to its doping amount. As the applied voltage increases, the doping amount of elements required to stabilize the structure must also be gradually increased. However, the higher the doping amount, the more difficult it is to achieve uniform distribution of elements in the bulk phase, resulting in element segregation and enrichment, which reduces its effect and brings a series of negative effects. Coating is the most commonly used technical means for the modification of high-voltage lithium cobalt oxide. Through the coating process, a relatively stable coating layer can be coated on the surface of the lithium cobalt oxide material, which can effectively improve the surface structural stability of the material and inhibit the occurrence of surface side reactions, oxygen evolution and cobalt dissolution. At present, the coating process generally adopts solid phase coating. Although this coating method is relatively simple, it is difficult to form a continuous and uniform coating layer on the surface. Although the liquid phase coating process can form a continuous and uniform coating layer structure, it has the characteristics of high cost and complex process. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a lithium cobalt oxide positive electrode material and a preparation method and application thereof. The preparation method provided by the present invention adopts doping and coating means to improve the performance of the lithium cobalt oxide positive electrode material, and can prepare a high-safety lithium cobalt oxide positive electrode material above 4.5V.

[0005] The present invention provides a method for preparing a lithium cobalt oxide positive electrode material, comprising the following steps:

[0006] a) mixing a cobalt source A, a lithium source C and a doping element D, performing a first sintering, and mechanically crushing to obtain a matrix lithium cobalt oxide;

[0007] b) mixing the cobalt source B, the lithium source C and the doping element E, performing a second sintering, and obtaining primary lithium cobalt oxide after air flow crushing is complete;

[0008] c) mixing the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and the additive, performing a third sintering, and mechanically crushing to obtain a sintered product having a core-shell structure;

[0009] d) mixing the calcined product with a core-shell structure obtained in step c) with a coating agent, performing a fourth sintering, and obtaining a lithium cobalt oxide positive electrode material after depolymerization;

[0010] There is no restriction on the order of step a) and step b).

[0011] The preparation method provided by the present invention achieves overall good interaction by selecting specific raw materials and cooperating with the above-mentioned specific steps. The prepared product has high structural stability and interface stability. It has good safety performance as the positive electrode material of the lithium-ion battery electrode sheet, and also has better high pressure resistance and high temperature resistance.

[0012] Preferably, the particle size of the cobalt source A in step a) is larger than the particle size of the cobalt source B in step b).

[0013] Preferably, the particle size D50 of the cobalt source A in step a) is 8 μm to 18 μm; the cobalt source A and the lithium source C are mixed in a lithium-cobalt molar ratio of (1 to 1.1):1;

[0014] The doping element D is selected from one or more of Ti, Mg, Ni, La, Zr, Y, Nb, B and Al; the content of the doping element D is 1000ppm to 10000ppm;

[0015] The temperature of the first sintering is 900° C. to 1100° C., the time is 2 h to 12 h, and the sintering atmosphere is air or oxygen.

[0016] Preferably, the particle size D50 of the cobalt source B in step b) is 1 μm to 6 μm; the cobalt source B and the lithium source C are mixed in a lithium-cobalt molar ratio of (0.95 to 1.1):1;

[0017] The doping element E is selected from one or more of Ti, Mg, Ni, La, Zr, Y, Nb, B and Al; the content of the doping element E is 2000ppm to 20000ppm;

[0018] The temperature of the second sintering is 600° C. to 900° C., the time is 2 h to 10 h, and the sintering atmosphere is air or oxygen.

[0019] Preferably, the additive in step c) is selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxalate;

[0020] The mass ratio of the matrix lithium cobalt oxide and the primary lithium cobalt oxide is (2-30):1; the dosage of the additive is 0.5%-2% of the total mass of the matrix lithium cobalt oxide and the primary lithium cobalt oxide.

[0021] Preferably, the temperature of the third sintering in step c) is 900° C. to 1100° C., the time is 4 h to 15 h, and the sintering atmosphere is air or oxygen.

[0022] Preferably, the temperature of the fourth sintering in step d) is 800° C. to 1000° C., the time is 4 h to 15 h, and the sintering atmosphere is air or oxygen.

[0023] The present invention also provides a lithium cobalt oxide positive electrode material, which is prepared by the preparation method described in the above technical solution.

[0024] The present invention also provides an electrode sheet, comprising the lithium cobalt oxide positive electrode material described in the above technical solution.

[0025] The present invention also provides a lithium ion battery, comprising the electrode sheet described in the above technical solution.

[0026] The present invention provides a lithium cobalt oxide positive electrode material and a preparation method and application thereof; the preparation method comprises the following steps: a) mixing a cobalt source A, a lithium source C and a doping element D, performing a first sintering, and mechanically crushing to obtain a matrix lithium cobalt oxide; b) mixing a cobalt source B, a lithium source C and a doping element E, performing a second sintering, and airflow crushing to obtain a primary lithium cobalt oxide; c) mixing the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and an additive, performing a third sintering, and mechanically crushing to obtain a sintered product having a core-shell structure; d) mixing the sintered product having a core-shell structure obtained in step c) with a coating agent, performing a fourth sintering, and depolymerizing to obtain a lithium cobalt oxide positive electrode material; there is no order restriction for steps a) and b). Compared with the prior art, the preparation method provided by the present invention uses doping and coating means to improve the performance of the lithium cobalt oxide positive electrode material, and can prepare a lithium cobalt oxide positive electrode material with high safety of more than 4.5V.

[0027] At the same time, the preparation method provided by the present invention has simple process, easily controllable conditions and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A flow chart showing the main idea of ​​the preparation method provided by the present invention;

[0029] Figure 2 This is a SEM characterization image of the lithium cobalt oxide obtained in step (1) of Example 1 of the present invention;

[0030] Figure 3 This is a SEM characterization image of the lithium cobalt oxide obtained in step (2) of Example 1 of the present invention;

[0031] Figure 4 This is a SEM characterization image of the lithium cobalt oxide obtained in step (3) of Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The present invention provides a method for preparing a lithium cobalt oxide positive electrode material, comprising the following steps:

[0034] a) mixing a cobalt source A, a lithium source C and a doping element D, performing a first sintering, and mechanically crushing to obtain a matrix lithium cobalt oxide;

[0035] b) mixing the cobalt source B, the lithium source C and the doping element E, performing a second sintering, and obtaining primary lithium cobalt oxide after air flow crushing is complete;

[0036] c) mixing the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and the additive, performing a third sintering, and mechanically crushing to obtain a sintered product having a core-shell structure;

[0037] d) mixing the calcined product with a core-shell structure obtained in step c) with a coating agent, performing a fourth sintering, and obtaining a lithium cobalt oxide positive electrode material after depolymerization;

[0038] There is no restriction on the order of step a) and step b).

[0039] See the flowchart of the preparation method provided by the present invention. Figure 1 As shown; the main idea is: first use cobalt sources with large and small particle sizes D50 to burn out large-size matrix cobalt oxide and primary cobalt oxide respectively, then mix and sinter them evenly into cobalt oxide with a core-shell structure, and then coat to form a three-layer structure, and finally sinter to obtain the overall product of cobalt oxide positive electrode material. The preparation method provided by the present invention achieves better overall interaction by selecting specific raw materials and coordinating the above-mentioned specific steps. The prepared product has high structural stability and interface stability, and has good safety performance as a positive electrode material for lithium ion battery electrode sheets, and also has better high-voltage resistance and high-temperature resistance.

[0040] The present invention first mixes a cobalt source A, a lithium source C and a doping element D, performs a first sintering, and obtains a matrix lithium cobalt oxide after mechanical crushing; at the same time, a cobalt source B, a lithium source C and a doping element E are mixed, and then a second sintering is performed, and primary lithium cobalt oxide is obtained after air flow crushing is complete.

[0041] In the present invention, the particle size of the cobalt source A is greater than that of the cobalt source B; on this basis, the matrix lithium cobaltate obtained from the cobalt source A with a large particle size also has a larger particle size than the primary lithium cobaltate obtained from the cobalt source B with a small particle size, so that in the subsequent steps, the two can form a situation where the primary lithium cobaltate with a small particle size covers the matrix lithium cobaltate with a large particle size, thereby obtaining a sintered product with a core-shell structure after sintering. It can be seen from this that the preparation method provided by the present invention can form a special core-shell structure, and a layer of lithium cobaltate shell structure with a more stable structure is coated on the surface of the lithium cobaltate matrix. This overall structure can improve the structural stability and interface stability of the material under high-voltage charge and discharge conditions, thereby effectively inhibiting the side reactions and phase changes on the surface interface of the material, so that the material has good safety performance, and at the same time has better high-voltage resistance and high-temperature resistance.

[0042] In the present invention, the cobalt source A is preferably selected from one or more of cobalt tetroxide, cobalt hydroxide, cobalt carbonate and cobalt sulfate, and is more preferably cobalt tetroxide; the particle size D50 of the cobalt source A is preferably 8 μm to 18 μm; the present invention has no special restrictions on the source of the cobalt source A, and commercially available products well known to those skilled in the art can be used.

[0043] In the present invention, the lithium source C is preferably selected from one or more of lithium carbonate, lithium hydroxide and lithium nitrate, more preferably lithium carbonate; the present invention has no special restrictions on the source of the lithium source C, and commercially available products known to those skilled in the art can be used.

[0044] In the present invention, the cobalt source A and the lithium source C are preferably mixed in a lithium-cobalt molar ratio of (1 to 1.1):1; the present invention adopts the above-mentioned specific types of cobalt source A and lithium source C, and mixes them in a specific ratio, which can prepare matrix lithium cobalt oxide after sintering, which is used for the subsequent further preparation of lithium cobalt oxide positive electrode materials.

[0045] In the present invention, the doping element D is preferably selected from one or more of Ti, Mg, Ni, La, Zr, Y, Nb, B and Al; the content of the doping element D is preferably 1000ppm to 10000ppm, more preferably 4000ppm to 10000ppm. The present invention has no particular restrictions on the source of the doping element D, and commercially available products known to those skilled in the art can be used.

[0046] In a preferred embodiment of the present invention, the doping element D is aluminum oxide, magnesium oxide and titanium dioxide with element doping amounts of 2000ppm to 5000ppm, 1000ppm to 3000ppm and 1000ppm to 2000ppm respectively.

[0047] The present invention selects a doping element D with a specific content limit, with the aim of rationally designing the doping amount of the core structure of the material according to the material performance requirements, thereby effectively avoiding the occurrence of element enrichment and segregation, and improving the batch stability and capacity of the material.

[0048] In the present invention, the temperature of the first sintering is preferably 900°C to 1100°C, the time of the first sintering is preferably 2h to 12h, and the sintering atmosphere is air or oxygen. The present invention adopts the above sintering process to prepare the matrix lithium cobalt oxide that meets the requirements of the present invention.

[0049] In the present invention, the cobalt source B is preferably selected from one or more of cobalt tetroxide, cobalt hydroxide, cobalt carbonate and cobalt sulfate, and is more preferably cobalt tetroxide; the particle size D50 of the cobalt source B is preferably 1 μm to 6 μm; the present invention has no special restrictions on the source of the cobalt source B, and commercially available products well known to those skilled in the art can be used.

[0050] In the present invention, the lithium source C is the same as that in the above technical solution and will not be described in detail here.

[0051] In the present invention, the cobalt source B and the lithium source C are preferably mixed in a lithium-cobalt molar ratio of (0.95-1.1):1; the present invention adopts the above-mentioned specific types of cobalt source B and lithium source C, and mixes them in a specific ratio, so that primary lithium cobalt oxide can be prepared after sintering, which can be used for the subsequent further preparation of lithium cobalt oxide positive electrode materials.

[0052] In the present invention, the doping element E is preferably selected from one or more of Ti, Mg, Ni, La, Zr, Y, Nb, B and Al; the content of the doping element E is preferably 2000ppm to 20000ppm, more preferably 7000ppm to 16000ppm. The present invention has no special restrictions on the source of the doping element E, and commercially available products known to those skilled in the art can be used.

[0053] In a preferred embodiment of the present invention, the doping element E is aluminum oxide, magnesium oxide and titanium dioxide with element doping amounts of 5000ppm to 10000ppm, 1000ppm to 3000ppm and 1000ppm to 3000ppm respectively.

[0054] The present invention selects a doping element E with a limited specific content, with the aim of rationally designing the doping amount of the outer structure of the material according to the material performance requirements, thereby effectively avoiding the occurrence of element enrichment and segregation, and improving the batch stability and capacity of the material.

[0055] In the present invention, the doping element D and the doping element E may be selected from the same or different doping elements.

[0056] In the present invention, the temperature of the second sintering is preferably 600°C to 900°C, the time of the second sintering is preferably 2h to 10h, and the sintering atmosphere is air or oxygen. The present invention adopts the above sintering process to prepare primary lithium cobalt oxide that meets the requirements of the present invention.

[0057] Afterwards, the present invention mixes the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and the additive, performs a third sintering, and obtains a sintered product with a core-shell structure after mechanical crushing.

[0058] It can be seen that the present invention first uses a cobalt source with a smaller particle size and a higher specific surface area to generate lithium cobalt oxide with a smaller particle size and a lower crystallinity, and then coats it on the surface of the inner core through a melting reaction to form a shell structure; since the cobalt source used in the outer shell structure has a small particle size and a high specific surface area, it is conducive to the high-content element doping process.

[0059] In the present invention, the additive has a melting-assisting effect, promoting the fusion of small particles and large particles, and is preferably selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxalate, and more preferably lithium carbonate. The present invention has no particular limitation on the source of the additive, and commercially available products known to those skilled in the art can be used.

[0060] In the present invention, the mass ratio of the matrix lithium cobalt oxide and the primary lithium cobalt oxide is preferably (2-30):1, more preferably (5-10):1; the amount of the additive is preferably 0.5%-2% of the total mass of the matrix lithium cobalt oxide and the primary lithium cobalt oxide, more preferably 1%; the present invention adopts the above-mentioned specific ratio of matrix lithium cobalt oxide and primary lithium cobalt oxide to mix, and can prepare a sintered product with a core-shell structure after sintering, which is used for the subsequent further preparation of lithium cobalt oxide positive electrode materials.

[0061] In the present invention, the temperature of the third sintering is preferably 900°C to 1100°C, the time of the third sintering is preferably 4h to 15h, and the sintering atmosphere is air or oxygen. The present invention adopts the above sintering process to prepare a sintered product with a core-shell structure that meets the requirements of the present invention.

[0062] After obtaining the calcined product having a core-shell structure, the present invention mixes the calcined product having a core-shell structure with a coating agent, performs a fourth sintering, and obtains a lithium cobalt oxide positive electrode material after depolymerization.

[0063] The present invention adopts dry coating, and the coating agent can be a coating agent used for conventional lithium cobalt oxide coating well known to those skilled in the art, and the present invention has no special restrictions on this. In a preferred embodiment of the present invention, the coating agent is 5% to 6% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.05% to 0.15% (mass percentage of lithium cobalt oxide) of nano aluminum oxide and 0.04% to 0.06% (mass percentage of lithium cobalt oxide) of nano titanium dioxide.

[0064] In the present invention, the temperature of the fourth sintering is preferably 800°C to 1000°C, the time of the fourth sintering is preferably 4h to 15h, and the sintering atmosphere is air or oxygen. The present invention adopts the above sintering process to prepare a lithium cobalt oxide positive electrode material that meets the requirements of the present invention.

[0065] The preparation method provided by the present invention uses doping and coating means to improve the performance of lithium cobalt oxide positive electrode materials, but has a major breakthrough in the selection of its doping method and coating process, and obtains unexpected results, realizes a special core-shell structure design, and forms a layer of lithium cobalt oxide structure with a more stable structure on the surface of lithium cobalt oxide, which can effectively inhibit the occurrence of side reactions and phase changes on the surface of the material, and can also avoid element enrichment and segregation caused by excessive doping to the greatest extent, while improving the capacity of lithium cobalt oxide materials at high voltages. Therefore, the prepared lithium cobalt oxide positive electrode material has excellent capacity retention and good safety at a voltage of more than 4.5V.

[0066] Meanwhile, the preparation method of the present invention is simple and can be achieved by only adopting the traditional high-temperature solid phase and general dry mixing, and is easy to realize large-scale industrial production.

[0067] The present invention also provides a lithium cobalt oxide positive electrode material, which is prepared by the preparation method described in the above technical solution.

[0068] The present invention also provides an electrode sheet, comprising the lithium cobalt oxide positive electrode material described in the above technical solution. The present invention has no special restrictions on the specific preparation method of the electrode sheet, and the preparation process of the electrode sheet using the lithium cobalt oxide positive electrode material well known to those skilled in the art can be used.

[0069] The present invention also provides a lithium ion battery, comprising the electrode sheet described in the above technical solution.

[0070] Compared with the prior art, the lithium cobalt oxide positive electrode material and the preparation method thereof provided by the present invention have the following beneficial effects:

[0071] (1) The present invention adopts a special core-shell structure design, and a layer of lithium cobalt oxide shell structure with a more stable structure is coated on the surface of the lithium cobalt oxide matrix by melting. This structure can improve the structural stability and interface stability of the material under high voltage charging and discharging conditions, and can effectively inhibit the side reactions and phase changes on the surface and interface of the material, so that the material has good safety performance, and at the same time has better high voltage resistance and high temperature resistance.

[0072] (2) The present invention adopts a core-shell structure design, and the doping amount of the core structure of the material can be reasonably designed according to the material performance requirements, which can effectively avoid the occurrence of element enrichment and segregation, and improve the batch stability and capacity of the material.

[0073] (3) The present invention adopts a special core-shell structure design, firstly adopts a cobalt source with a smaller particle size and a higher specific surface area to generate lithium cobalt oxide with a smaller particle size and a lower crystallinity, and then coats it on the surface of the inner core through a melting reaction to form an outer shell structure; since the cobalt source used in the outer shell structure has a small particle size and a high specific surface area, it is conducive to the high-content element doping process.

[0074] (4) Compared with the traditional doping and coating modification methods, the present invention can improve the stability of the outer layer structure of lithium cobalt oxide through a special core-shell structure design. This structure can effectively inhibit the occurrence of side reactions and phase changes on the surface of the material, and can also avoid element enrichment and segregation caused by excessive doping to the greatest extent, while improving the capacity of the lithium cobalt oxide material under high voltage; therefore, the lithium cobalt oxide positive electrode material of the present invention has excellent capacity retention and good safety at a voltage above 4.5V.

[0075] (5) The preparation method of the present invention is simple and can be achieved by using only the traditional high-temperature solid phase and general dry mixing, and is easy to realize large-scale industrial production.

[0076] The present invention provides a lithium cobalt oxide positive electrode material and a preparation method and application thereof; the preparation method comprises the following steps: a) mixing a cobalt source A, a lithium source C and a doping element D, performing a first sintering, and mechanically crushing to obtain a matrix lithium cobalt oxide; b) mixing a cobalt source B, a lithium source C and a doping element E, performing a second sintering, and airflow crushing to obtain a primary lithium cobalt oxide; c) mixing the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and an additive, performing a third sintering, and mechanically crushing to obtain a sintered product having a core-shell structure; d) mixing the sintered product having a core-shell structure obtained in step c) with a coating agent, performing a fourth sintering, and depolymerizing to obtain a lithium cobalt oxide positive electrode material; there is no order restriction for steps a) and b). Compared with the prior art, the preparation method provided by the present invention uses doping and coating means to improve the performance of the lithium cobalt oxide positive electrode material, and can prepare a lithium cobalt oxide positive electrode material with high safety of more than 4.5V.

[0077] At the same time, the preparation method provided by the present invention has simple process, easily controllable conditions and broad application prospects.

[0078] In order to further illustrate the present invention, the following examples are provided for detailed description.

[0079] Example 1

[0080] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.05, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 8 μm to 15 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 2000 ppm, 2000 ppm and 1000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 1000° C. for 8 h; the sintering atmosphere is air; and the sintered product is then subjected to conventional mechanical crushing to obtain a matrix lithium cobalt oxide.

[0081] (2) According to the lithium-cobalt molar ratio (Li / Co) of 1.03, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 1 μm to 3 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 5000 ppm, 2000 ppm and 2000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 800° C. for 6 hours; the sintering atmosphere is air; and the sintered product is thoroughly crushed (airflow crushing) to obtain primary lithium cobalt oxide powder.

[0082] (3) The base lithium cobalt oxide described in step (1) and the primary lithium cobalt oxide described in step (2) are uniformly mixed in a mass ratio of 5:1, and 1% lithium carbonate is added at the same time, and then sintered at a high temperature of 1000° C. for 10 hours in an air atmosphere; after pulverization, a sintered lithium cobalt oxide with a core-shell structure is obtained.

[0083] (4) The lithium cobalt oxide described in step (3) is mixed evenly with a coating agent to obtain a secondary mixed material, wherein the coating agent is 5% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of lithium cobalt oxide) of nano-titanium dioxide; then the mixed material is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain a lithium cobalt oxide positive electrode material with a core-shell structure.

[0084] Scanning electron microscopy (SEM) was used to examine the steps (1) in Example 1. Figure 2 Step (2) Figure 3 , step (3) is as follows Figure 4 (After burning, the small particles will melt into the surface of the large particles to form new large particles) The obtained lithium cobalt oxide is characterized.

[0085] Example 2

[0086] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.06, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 10 μm to 18 μm are weighed respectively, and aluminum oxide, zirconium oxide and titanium dioxide are weighed respectively according to element doping amounts of 4000 ppm, 2000 ppm and 1000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 1000° C. for 8 hours; the sintering atmosphere is air; and the sintered product is subjected to conventional mechanical crushing to obtain a matrix lithium cobalt oxide.

[0087] (2) According to the lithium-cobalt molar ratio (Li / Co) of 1.04, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 1 μm to 4 μm are weighed respectively, and aluminum oxide, zirconium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 8000 ppm, 2000 ppm and 2000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 800° C. for 6 hours; the sintering atmosphere is air; and the sintered product is thoroughly crushed (airflow crushing) to obtain primary lithium cobalt oxide powder.

[0088] (3) The base lithium cobalt oxide described in step (1) and the primary lithium cobalt oxide described in step (2) are uniformly mixed in a mass ratio of 5:1, and 1% lithium carbonate is added at the same time, and then sintered at a high temperature of 1000° C. for 8 hours in an air atmosphere; after pulverization, a sintered lithium cobalt oxide with a core-shell structure is obtained.

[0089] (4) The lithium cobalt oxide described in step (3) is mixed evenly with a coating agent to obtain a secondary mixed material, wherein the coating agent is 5% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of lithium cobalt oxide) of nano-titanium dioxide; then the mixed material is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain the lithium cobalt oxide positive electrode material with a core-shell structure.

[0090] Example 3

[0091] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.07, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 8 μm to 18 μm are weighed respectively, and aluminum oxide, lanthanum oxide and titanium dioxide are weighed respectively according to element doping amounts of 5000 ppm, 2000 ppm and 1000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 1000° C. for 8 h; the sintering atmosphere is air; and the sintered product is subjected to conventional mechanical crushing to obtain a matrix lithium cobalt oxide.

[0092] (2) According to the lithium-cobalt molar ratio (Li / Co) of 1.04, cobalt oxide and battery-grade lithium carbonate raw materials with a particle size D50 of 1 μm to 5 μm are weighed respectively, and aluminum oxide, lanthanum oxide and titanium dioxide are weighed respectively according to the element doping amounts of 10000 ppm, 2000 ppm and 2000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 800° C. for 6 hours; the sintering atmosphere is air; and the sintered product is thoroughly crushed (airflow crushing) to obtain primary lithium cobalt oxide powder.

[0093] (3) The base lithium cobalt oxide described in step (1) and the primary lithium cobalt oxide described in step (2) are uniformly mixed in a mass ratio of 5:1, and 1% lithium carbonate is added at the same time, and then sintered at a high temperature of 1000° C. for 10 hours in an air atmosphere; after pulverization, a sintered lithium cobalt oxide with a core-shell structure is obtained.

[0094] (4) The lithium cobalt oxide described in step (3) is mixed evenly with a coating agent to obtain a secondary mixed material, wherein the coating agent is 5% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of lithium cobalt oxide) of nano-titanium dioxide; then the mixed material is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain the lithium cobalt oxide positive electrode material with a core-shell structure.

[0095] Example 4

[0096] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.05, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 12 μm to 18 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to element doping amounts of 3000 ppm, 2000 ppm and 1000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 1000° C. for 8 h; the sintering atmosphere is air; and the sintered product is then subjected to conventional mechanical crushing to obtain a matrix lithium cobalt oxide.

[0097] (2) According to the lithium-cobalt molar ratio (Li / Co) of 1.03, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 2 μm to 6 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 8000 ppm, 2000 ppm and 2000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 800° C. for 6 hours; the sintering atmosphere is air; and the sintered product is thoroughly crushed (airflow crushing) to obtain primary lithium cobalt oxide powder.

[0098] (3) The base lithium cobalt oxide described in step (1) and the primary lithium cobalt oxide described in step (2) are uniformly mixed in a mass ratio of 10:1, and 1% by mass of lithium carbonate is added, followed by sintering at a high temperature of 1000° C. for 10 h in an air atmosphere; after pulverization, a sintered lithium cobalt oxide having a core-shell structure is obtained.

[0099] (4) The lithium cobalt oxide described in step (3) is mixed evenly with a coating agent to obtain a secondary mixed material, wherein the coating agent is 6% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of lithium cobalt oxide) of nano-titanium dioxide; then the mixed material is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain the lithium cobalt oxide positive electrode material with a core-shell structure.

[0100] Comparative Example 1

[0101] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.05, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 8 μm to 15 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 500 ppm, 100 ppm and 100 ppm, and they are fully mixed; then, they are placed under high temperature conditions of 1000° C. for 8 hours; the sintering atmosphere is air; and the sintered product is then subjected to conventional mechanical crushing to obtain matrix lithium cobalt oxide.

[0102] (2) According to the lithium-cobalt molar ratio (Li / Co) of 1.03, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 1 μm to 5 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 500 ppm, 100 ppm and 100 ppm, and they are fully mixed; then, they are sintered at a high temperature of 800° C. for 6 hours; the sintering atmosphere is air; and the sintered product is thoroughly crushed (airflow crushing) to obtain primary lithium cobalt oxide powder.

[0103] (3) The base lithium cobalt oxide described in step (1) and the primary lithium cobalt oxide described in step (2) are uniformly mixed in a mass ratio of 5:1, and 1% lithium carbonate is added at the same time, and then sintered at a high temperature of 1000° C. for 10 hours in an air atmosphere; after pulverization, a sintered lithium cobalt oxide with a core-shell structure is obtained.

[0104] (4) The lithium cobalt oxide described in step (3) is mixed evenly with a coating agent to obtain a secondary mixed material, wherein the coating agent is 5% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of lithium cobalt oxide) of nano-titanium dioxide; then the mixed material is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain the lithium cobalt oxide positive electrode material with a core-shell structure.

[0105] Comparative Example 2

[0106] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.05, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 10 μm to 18 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to element doping amounts of 10000 ppm, 2000 ppm and 2000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 1000° C. for 8 h; the sintering atmosphere is air; and the sintered product is subjected to conventional mechanical crushing to obtain a matrix lithium cobalt oxide.

[0107] (2) According to the lithium-cobalt molar ratio (Li / Co) of 1.03, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 2 μm to 6 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 18000 ppm, 2000 ppm and 2000 ppm, and they are fully mixed; then, they are placed at a high temperature of 800° C. for 6 hours; the sintering atmosphere is air; and the sintered product is thoroughly crushed (airflow crushing) to obtain primary lithium cobalt oxide powder.

[0108] (3) The base lithium cobalt oxide described in step (1) and the primary lithium cobalt oxide described in step (2) are uniformly mixed in a mass ratio of 5:1, and 1% lithium carbonate is added at the same time, and then sintered at a high temperature of 1000° C. for 10 hours in an air atmosphere; after pulverization, a sintered lithium cobalt oxide with a core-shell structure is obtained.

[0109] (4) The lithium cobalt oxide described in step (3) is mixed evenly with a coating agent to obtain a secondary mixed material, wherein the coating agent is 5% (mass percentage of lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of lithium cobalt oxide) of nano-titanium dioxide; then the mixed material is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain the lithium cobalt oxide positive electrode material with a core-shell structure.

[0110] Comparative Example 3

[0111] (1) According to a lithium-cobalt molar ratio (Li / Co) of 1.05, cobalt tetraoxide and battery-grade lithium carbonate raw materials with a particle size D50 of 8 μm to 15 μm are weighed respectively, and aluminum oxide, magnesium oxide and titanium dioxide are weighed respectively according to the element doping amounts of 2000 ppm, 2000 ppm and 1000 ppm, and they are fully mixed; then, they are sintered at a high temperature of 1000° C. for 8 h; the sintering atmosphere is air; and the sintered product is then subjected to conventional mechanical crushing to obtain a matrix lithium cobalt oxide.

[0112] (2) The matrix lithium cobalt oxide described in step (1) is uniformly mixed with a coating agent to obtain a secondary mixed material, wherein the coating agent is 5% (mass percentage of the matrix lithium cobalt oxide) of cobaltous hydroxide, 0.1% (mass percentage of the matrix lithium cobalt oxide) of nano-alumina and 0.05% (mass percentage of the matrix lithium cobalt oxide) of nano-titanium dioxide; then the mixture is sintered at a high temperature of 900° C. for 10 h, and then crushed and depolymerized to obtain a lithium cobalt oxide positive electrode material.

[0113] Performance Testing

[0114] The electrochemical performance of the lithium cobalt oxide materials obtained in the above examples and comparative examples was tested, and the results are shown in Tables 1-2.

[0115] Table 1 Initial specific capacity data of lithium cobalt oxide materials obtained in Examples and Comparative Examples

[0116]

[0117] Battery test conditions: room temperature 25℃; voltage range: 3.0V~4.53V; 0.1C charge and discharge.

[0118] Table 2 Capacity retention data of lithium cobalt oxide materials obtained in Examples and Comparative Examples

[0119] Capacity retention rate 20 weeks 40 weeks 60 weeks 80 weeks Example 1 94.5 89.9 84.9 78.6 Example 2 94.7 90.6 85.7 80.5 Example 3 96.1 92.9 87.5 84.2 Example 4 96.8 92.2 86.8 82.7 Comparative Example 1 74.1 61.9 51.9 42.6 Comparative Example 2 88.8 81.6 77.8 70.5 Comparative Example 3 80.6 72.4 62.3 48.9

[0120] Battery test conditions: high temperature 45℃; voltage range: 3.0V~4.55V; 1C charge and discharge.

[0121] It can be seen from the above results that the lithium cobalt oxide positive electrode material with a core-shell structure provided in the present application has good initial specific capacity and capacity retention rate in the application of the battery. When the lithium cobalt oxide positive electrode material in Comparative Example 3 does not contain lithium cobalt oxide with a small particle size, the initial specific capacity and capacity retention rate of the obtained positive electrode material in the battery are both low, indicating that the surface layer of the lithium cobalt oxide with a core-shell structure provided in the present application forms a layer of lithium cobalt oxide structure with a more stable structure, which can effectively inhibit the occurrence of side reactions and phase changes on the surface of the material, and can also minimize the element enrichment and segregation caused by excessive doping, while improving the capacity of the lithium cobalt oxide material under high voltage. Referring to Comparative Examples 1 and 2, when the amount of doping elements and the ratio of the matrix lithium cobalt oxide and the primary lithium cobalt oxide are changed, the initial specific capacity and capacity retention rate both decrease.

[0122] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a lithium cobalt oxide positive electrode material, comprising the following steps: a) mixing the cobalt source A, the lithium source C and the doping element D, performing the first sintering, and mechanically crushing to obtain the matrix lithium cobalt oxide; b) mixing the cobalt source B, the lithium source C and the doping element E, performing a second sintering, and obtaining primary lithium cobalt oxide after air flow crushing; c) mixing the matrix lithium cobalt oxide obtained in step a), the primary lithium cobalt oxide obtained in step b) and the additive, performing a third sintering, and mechanically crushing to obtain a sintered product having a core-shell structure; d) mixing the calcined product with a core-shell structure obtained in step c) with a coating agent, performing a fourth sintering, and obtaining a lithium cobalt oxide positive electrode material after depolymerization; There is no order restriction for step a) and step b); In step a), the particle size D50 of the cobalt source A is 8 μm to 18 μm; the cobalt source A and the lithium source C are mixed in a lithium-cobalt molar ratio of (1 to 1.1):1; The doping element D is selected from one or more of Ti, Mg, Ni, La, Zr, Y, Nb, B and Al; the content of the doping element D is 1000ppm~10000ppm; The first sintering temperature is 900°C to 1100°C, the time is 2h to 12h, and the sintering atmosphere is air or oxygen; The particle size D50 of the cobalt source B in step b) is 1 μm to 6 μm; the cobalt source B and the lithium source C are mixed according to a lithium-cobalt molar ratio of (0.95 to 1.1):1; The doping element E is selected from one or more of Ti, Mg, Ni, La, Zr, Y, Nb, B and Al; the content of the doping element E is 2000ppm~20000ppm; The second sintering temperature is 600°C to 900°C, the time is 2h to 10h, and the sintering atmosphere is air or oxygen; In step c), the additive is selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxalate; The mass ratio of the matrix lithium cobalt oxide and the primary lithium cobalt oxide is (2-30):1; the amount of the additive is 0.5%-2% of the total mass of the matrix lithium cobalt oxide and the primary lithium cobalt oxide.

2. The preparation method according to claim 1, characterized in that: The temperature of the third sintering in step c) is 900° C. to 1100° C., the time is 4 h to 15 h, and the sintering atmosphere is air or oxygen.

3. The preparation method according to claim 1, characterized in that: The temperature of the fourth sintering in step d) is 800° C. to 1000° C., the time is 4 h to 15 h, and the sintering atmosphere is air or oxygen.

4. A lithium cobalt oxide positive electrode material, characterized in that: The method is prepared according to any one of claims 1 to 3.

5. An electrode sheet, characterized in that: Including the lithium cobalt oxide positive electrode material as described in claim 4.

6. A lithium ion battery, characterized in that: Comprising the electrode sheet as claimed in claim 5.

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