Cobaltous oxide, cobalt carbonate and preparation method, positive electrode material and lithium ion battery

Abstract

The present application provides a cobalt tetroxide, cobalt carbonate and preparation method, positive electrode material, lithium ion battery, which relates to the field of new energy technology. The cobalt tetroxide secondary particles are gradient doped with Al as a whole, and the core layer has a high doping amount, which improves the stability of the crystal structure of the LCO material and improves the cycle performance. The cobalt tetroxide includes a core layer and a coating layer covering the core layer. The cobalt content decreases layer by layer from the inside to the outside, reducing the surface Co 4+ The core layer is a functional layer with a large volume share and a high cobalt content, which can increase capacity and improve cycle performance. The coating layer is a modified layer that is coated on the outside of the core layer. The coating layer is very thin and the total content of doped elements increases in a gradient, which can enhance the material's specific properties and improve the overall performance of LCO.

Description

Technical Field

[0001] The present application relates to the field of new energy technology, and in particular to cobalt tetroxide, cobalt carbonate and preparation methods, positive electrode materials, and lithium-ion batteries. Background Art

[0002] With the rapid development of technology, portable mobile devices have become ubiquitous in our daily lives, and people's requirements for mobile devices' battery life, size, and fast charging capabilities have also increased. Lithium cobalt oxide batteries, with their high volumetric energy density and other advantages, are widely used in the field of 3C digital products.

[0003] The battery life and cycle life of lithium-ion secondary batteries are of widespread concern within the industry. Currently, the theoretical voltage of lithium cobalt oxide is at least 4.2V, with a theoretical specific capacity of 274mA / g. Currently, the horizontal voltage can reach above 4.4V, with an actual capacity of 180mA / g, and this capacity significantly decreases with increasing cycle times. To achieve higher capacity, lithium cobalt oxide is being developed towards higher voltages above 4.5V. The goal is to allow more lithium ions to escape from the crystal structure at higher voltages, thereby increasing the capacity of lithium cobalt oxide.

[0004] At present, the industry generally adopts the doping method to improve the structural stability of the material under high voltage by changing the crystal structure of the LCO material. However, as the types and amounts of doping elements increase, the uniformity of the doping elements in LCO becomes very important, otherwise the capacity and cycle performance of the battery material will decline.

[0005] In addition, due to the diversity of application scenarios of lithium-ion secondary batteries, in addition to the requirements for high capacity and long cycle core functions, differentiated demands will also arise. Among lithium cobalt oxide positive electrode materials, cobalt tetroxide is its most important raw material. The performance of cobalt tetroxide determines the performance of lithium cobalt oxide to a certain extent, which also puts forward different requirements for the positive electrode material precursor, such as improving rate performance and more outstanding cycle performance.

[0006] How to ensure the uniformity of doping elements in LCO for different application scenarios of lithium-ion secondary batteries while taking into account battery capacity and core cycle functions, while meeting the differentiated needs of different customers through a set of adjustable technical solutions, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this application is to solve the above-mentioned technical problems and provide a cobalt tetroxide, cobalt carbonate and preparation method, positive electrode material, and lithium-ion battery. While ensuring that the core layer meets the high capacity and long cycle functions, the number of layers and doping elements of the coating layer can be adjusted according to the differentiated needs of different customers through a set of adjustable technical solutions to prepare products that meet the needs of different customers.

[0008] To achieve the above objectives, the present application provides a cobalt oxide, comprising a core layer and a coating layer coated outside the core layer, see Figure 33 ; Both the core layer and the cladding layer are doped with Al, and the Al doping content of the core layer is higher than that of the cladding layer;

[0009] Preferably, the cobalt content of the cobalt trioxide decreases layer by layer from the core layer to the coating layer.

[0010] Preferably, cobalt trioxide satisfies at least one of the following conditions A to E:

[0011] A. The coating layer of cobalt trioxide is 1 to 5 layers, for example, 1 layer, 2 layers, 3 layers, 4 layers or 5 layers;

[0012] B. The ratio of the mass of doped Al in the core layer of the cobalt oxide to the total mass of the metal in the core layer of the cobalt oxide is: 0.40-1.20wt%, for example, 0.40-0.80wt%, or 0.80-1.00wt%, or 1.00-1.20wt%, more specifically, for example, 0.40wt%, 0.50wt%, 0.60wt%, 0.70wt%, 0.80wt%, 0.85wt%, 0.90wt%, 0.95wt%, 1.00wt%, 1.05wt%, 1.10wt% or 1.20wt%;

[0013] C. The ratio of the mass of doped Al in the coating layer of cobalt oxide to the total mass of metal in cobalt oxide is: 0.02-0.40wt%, for example, 0.02-0.1wt%, or 0.05-0.15wt%, or 0.1-0.4wt%, more specifically, for example, 0.02wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt% or 0.4wt%;

[0014] D. When the cobalt oxide coating layer is one layer, the ratio of the molar amount of cobalt in the coating layer to the total molar amount of metal in the cobalt oxide coating layer is ≤70 mol%, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 67 mol%, 69 mol% or 70 mol%;

[0015] E. When the number of cobalt oxide coating layers is 2 to 5, the ratio of the molar amount of cobalt in the outermost layer of the coating layer to the molar amount of the total metal in the outermost layer of the cobalt oxide coating layer is ≤ 70 mol%, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 67 mol%, 69 mol% or 70 mol%;

[0016] F. The diameter of the core layer of cobalt trioxide is 5.0 to 18.0 μm, for example, 5.0 to 8.0 μm, or 8.0 to 10.0 μm, or 10.0 to 13.0 μm, or 13.0 to 18.0 μm, more specifically, for example, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, or 18.0 μm;

[0017] G. When the coating layer of cobalt trioxide is one layer, the coating layer has a thickness of 0.10 to 1.0 μm, for example, 0.10 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm;

[0018] H. When the number of the cobalt oxide coating layer is 2 to 5, the thickness of a single layer in the coating layer is 0.10 to 1.0 μm, for example, 0.10 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm.

[0019] Preferably, the cobalt trioxide satisfies at least one of the following conditions I to L:

[0020] I. The core layer of cobalt trioxide also includes Ni and / or Mn;

[0021] J. When condition I is met, the ratio of the mass of Ni and Mn doped in the core layer of the cobalt oxide to the total metal mass in the core layer of the cobalt oxide is independently: 0.10-3.00wt%, for example, 0.10-0.80wt%, or 0.80-1.50wt%, or 1.50-3.00wt%, more specifically, for example, 0.10wt%, 0.50wt%, 0.8wt%, 1.00wt%, 1.20wt%, 1.30wt%, 1.40wt%, 1.50wt%, 1.60wt%, 1.70wt%, 1.80wt%, 1.90wt%, 2.00wt%, 2.10wt%, 2.20wt%, 2.30wt%, 2.40wt%, 2.60wt%, 2.80wt% or 3.00wt%;

[0022] K. The cobalt oxide coating layer further includes one or more doping elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba;

[0023] That is, in addition to being doped with Al, the coating layer of cobalt trioxide may be a layer doped with one of the above elements, or a layer doped with multiple elements. More specifically, when the coating layer is a single layer, in addition to being doped with Al, it may be doped with one of the above elements other than Al, or may be doped with multiple elements other than Al. When the coating layer is a multilayer layer, in addition to being doped with Al, it may be doped with only one of the above elements other than Al in each coating layer, or may be doped with multiple elements other than Al in each coating layer.

[0024] Preferably, when the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further includes one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0025] When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, and all layers other than the inner layer and the outer layer are intermediate layers, the inner layer of the coating layer further includes one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer further includes one or more of La, Zr, Y, Ti, and Sr; and the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0026] Among them, La and Zr form a stable solid phase layer, Ca and Ba doping replace part of Co, play a role in stabilizing the skeleton structure, and are more suitable for being placed in the inner layer or middle layer; La and Zr have large ion radius, which can increase the C axis distance of the unit cell and facilitate ion migration; Y, Ti, and Sr can all improve electrical conductivity, facilitate ion migration, and improve rate performance, and are more suitable for being placed in the inner layer or middle layer; Mg and Sr doping can effectively improve electrical conductivity, and the Mg / Ti mixed structure can inhibit material phase change and improve surface structure stability;

[0027] L. When condition K is met, the ratio of the mass of other doping elements except Al in the coating layer of cobalt oxide to the total metal mass in cobalt oxide is independently 0.01 to 0.40 wt%.

[0028] Preferably, cobalt trioxide satisfies at least one of the following conditions M to Q:

[0029] M. The porosity of the core layer of the cobalt oxide is 5.5-9.5%, for example, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0% or 9.5%, for example, 1.2%, 1.5%, 2.0%, 2.2%, 2.5%, 2.6%, 2.8%, 3.0%, 3.3% or 3.5%, and the overall porosity of the cobalt oxide is 4.5-7.5%, for example, 4.5%-5.0%, or 5.0%-5.5%, or 5.5%-6.0%, or 6.0%-7.5%.

[0030] N. The pore volume of the core layer of cobalt tetroxide is 0.004~0.015cm 3 / g, for example, 0.004 to 0.008 cm 3 / g, or 0.008~0.015cm 3 / g, the overall pore volume of cobalt trioxide is 0.002~0.080cm 3 / g, for example, 0.002 to 0.004 cm 3 / g, or 0.004~0.006cm 3 / g, or 0.006~0.009cm 3 / g, or 0.009~0.01cm 3 / g, or 0.01~0.05cm 3 / g, or 0.05~0.08cm 3 / g;

[0031] The porosity and pore volume of cobalt carbonate and cobalt oxide in this application were measured using a fully automatic surface area and pore size distribution analyzer (Model: BELPREP-VACII / BELSORP-MINI-X) manufactured by Microtrac Inc. (USA). The test principle is nitrogen adsorption, and the specific test method is based on the manufacturer's instrument operating procedures and the included workstation software. The test results differ from those calculated using software such as Avizo to calculate the ratio of pore area to total area in cross-sectional photographs.

[0032] O. The D50 of cobalt trioxide is 5.5 to 23.0 μm, for example, 5.5 to 10.0 μm, or 10.0 to 12.0 μm, or 12.0 to 15.0 μm, or 15.0 to 16.0 μm, or 16.0 to 17.0 μm, or 17.0 to 20.0 μm, or 20.0 to 23.0 μm;

[0033] P. The tap density of cobalt tetroxide is 2.0~3.0g / cm 3 , for example, it can be 2.0 to 2.3 g / cm 3 , or 2.3~2.5g / cm3 , or 2.5~2.6g / cm 3 , or 2.6~2.8g / cm 3 , or 2.8~3.0g / cm 3 ;

[0034] Q. The specific surface area of cobalt tetroxide is 2.0 to 15 m 2 / g, for example, 2.0 to 4.0 m 2 / g, or 4.0~6.0m 2 / g, or 6.0~10.0m 2 / g, or 10-15m 2 / g.

[0035] The second aspect of the present application further provides a cobalt carbonate, comprising a core layer and a coating layer coated outside the core layer, see Figure 33 ; Both the core layer and the cladding layer are doped with Al, and the Al doping content of the core layer is higher than that of the cladding layer;

[0036] Preferably, the cobalt content of the cobalt carbonate decreases layer by layer from the core layer to the coating layer.

[0037] Preferably, the cobalt carbonate satisfies at least one of the following conditions a to l:

[0038] a. The coating layer of cobalt carbonate is 1 to 5 layers, for example, 1 layer, 2 layers, 3 layers, 4 layers or 5 layers;

[0039] b. The ratio of the mass of doped Al in the core layer of cobalt carbonate to the total mass of metal in the core layer of cobalt carbonate is: 0.26 to 0.80wt%, for example, 0.26 to 0.30wt%, or 0.30 to 0.40wt%, or 0.40 to 0.50wt%, or 0.50 to 0.70wt%, or 0.70 to 0.80wt%, more specifically, for example, 0.26wt%, 0.30wt%, 0.35wt%, 0.40wt%, 0.50wt%, 0.60wt%, 0.70wt% or 0.80wt%;

[0040] c. The ratio of the mass of doped Al in the cobalt carbonate coating to the total mass of the metal in the cobalt carbonate is: 0.01 to 0.27 wt %, for example, 0.01 to 0.04 wt %, or 0.04 to 0.1 wt %, or 0.05 to 0.15 wt %, or 0.15 to 0.27 wt %, more specifically, for example, 0.01 wt %, 0.02 wt %, 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt %, 0.25 wt % or 0.27 wt %;

[0041] d. When the cobalt carbonate coating layer is 1 layer, the molar ratio of cobalt in the cobalt carbonate coating layer to the total molar amount of metal in the cobalt oxide coating layer is ≤70 mol%, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 67 mol%, 69 mol% or 70 mol%;

[0042] e. When the cobalt carbonate coating layer is 2 to 5 layers, the molar amount of cobalt in the outermost layer of the cobalt carbonate coating layer to the total molar amount of cobalt carbonate coating layer is ≤70mol%, for example, 50mol%, 55mol%, 60mol%, 65mol%, 67mol%, 69mol% or 70mol%;

[0043] f. The diameter of the core layer of cobalt carbonate is 8.0 to 23.0 μm, for example, 8.0 to 10.0 μm, or 10.0 to 13.0 μm, or 13.0 to 18.0 μm, 18.0 to 23.0 μm, more specifically, for example, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0 or 23.0 μm;

[0044] g. When the coating layer of cobalt carbonate is one layer, the coating layer thickness is 0.15 to 1.5 μm, preferably, the coating layer thickness is 0.15 to 0.5 μm; for example, it may be 0.15 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm, or 1.0 to 1.5 μm;

[0045] h. When the coating layer of cobalt carbonate is 2 to 5 layers, the thickness of the single layer in the coating layer is 0.15 to 1.5 μm, preferably, the thickness of the single layer of the coating layer is 0.15 to 0.5 μm; for example, it may be 0.15 to 0.30 μm, or 0.30 to 0.40 μm, or 0.40 to 0.50 μm, or 0.50 to 0.70 μm, or 0.70 to 1.0 μm, or 1.0 to 1.5 μm;

[0046] i. The core layer of cobalt carbonate also includes Ni and / or Mn;

[0047] j. When condition i is met, the ratio of the mass of Ni and Mn doped in the core layer of cobalt carbonate to the total mass of the metal in the core layer of cobalt carbonate is independently: 0.07 to 2.00 wt%, for example, 0.07 to 0.10 wt%, or 0.10 to 0.30 wt%, or 0.30 to 1.50 wt%, or 0.50 to 1.00 wt%, or 1.00 to 2.00 wt%, more specifically, for example, 0.07 wt%, 0.10 wt%, 0.50 wt%, 0.8 wt%, 1.00 wt%, 1.20 wt%, 1.30 wt%, 1.40 wt%, 1.50 wt%, 1.60 wt%, 1.70 wt%, 1.80 wt%, 1.90 wt% or 2.00 wt%;

[0048] k. The cobalt carbonate coating layer further includes one or more doping elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba; that is, the cobalt carbonate coating layer may be doped with one or more of the aforementioned elements in addition to Al; more specifically, when the cobalt carbonate coating layer is a single layer, it may be doped with one or more of the aforementioned elements in addition to Al; and when the cobalt carbonate coating layer is a multi-layer layer, each layer may be doped with only one of the aforementioned elements in addition to Al, or each layer may be doped with multiple of the aforementioned elements in addition to Al.

[0049] Preferably, when the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further includes one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0050] When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, and all layers other than the inner layer and the outer layer are intermediate layers. The inner layer of the coating layer further includes one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer further includes one or more of La, Zr, Y, Ti, and Sr; and the outer layer of the coating layer further includes one or more of Mg, Zr, Ti, and Sr;

[0051] l. When condition k is met, the ratio of the mass of the doping elements other than Al in the cobalt carbonate coating layer to the total metal mass in the cobalt carbonate is independently: 0.01 to 0.30 wt%.

[0052] Preferably, the cobalt carbonate satisfies at least one of the following conditions m to q:

[0053] m. The porosity of the core layer of cobalt carbonate is 15 to 25%, for example, 15 to 17%, or 17 to 18%, or 18 to 20%, or 21 to 23%, or 23 to 25%, and the overall porosity of cobalt carbonate is 14 to 25%, for example, 14 to 17%, or 17 to 20%, or 20 to 25%, or 20 to 23%, or 23 to 24%, or 24 to 25%;

[0054] n. The pore volume of the core layer of cobalt carbonate is 0.08~0.30cm 3 / g, for example, 0.08 to 0.12 cm 3 / g, or 0.12~0.16cm 3 / g, or 0.16~0.20cm 3 / g, or 0.20~0.25cm 3 / g, or 0.25~0.30cm 3 / g, and the overall pore volume of cobalt carbonate is 0.05~0.25cm 3 / g, for example, 0.05 to 0.08 cm 3 / g, or 0.08~0.10cm 3 / g, or 0.10~0.16cm 3 / g, or 0.10~0.13cm 3 / g, or 0.13~0.16cm 3 / g, or 0.16~0.20cm 3 / g, or 0.20~0.25cm 3 / g;

[0055] o. The D50 of cobalt carbonate is 8.7 to 30.0 μm, for example, 8.7 to 12.0 μm, or 12.0 to 15.0 μm, or 15.0 to 17.0 μm, or 17.0 to 19.0 μm, or 19.0 to 23.0 μm, or 19.0 to 20.0 μm, or 20.0 to 21.0 μm, or 21.0 to 22.0 μm, or 23.0 to 30.0 μm;

[0056] p. The specific surface area of cobalt carbonate is 50 to 150 m 2 / g, for example, 50 to 70 m 2 / g, or 70-90m 2 / g, or 90-100m 2 / g, or 100-110m 2 / g, or 110-120m 2 / g, or 120-150m 2 / g;

[0057] q. The tap density of cobalt carbonate is 1.5-2.0 g / cm 3 , for example, it can be 1.5 to 1.6 g / cm 3 , or 1.6~1.7g / cm 3 , or 1.7~1.8g / cm 3 , or 1.8~1.9g / cm 3 , or 1.9~2.0g / cm 3 .

[0058] The third aspect of the present application further provides a method for preparing cobalt carbonate, comprising:

[0059] The core layer cobalt salt solution and the precipitant solution are added to a reactor containing a base liquid to react, the flow rate of the core layer cobalt salt solution increases with the increase of the material particle size, the flow rate of the precipitant solution increases with the increase of the flow rate of the core layer cobalt salt solution, and the stirring speed of the reactor decreases with the increase of the material particle size. The reaction is continued until the particle size D50 is 8.0 to 23.0 μm, thereby obtaining a cobalt carbonate core layer;

[0060] The coating layer cobalt salt solution and the precipitant solution are sequentially added into a reactor containing a cobalt carbonate core layer to react until the growth of each coating layer is completed to obtain cobalt carbonate.

[0061] The material is a growing cobalt carbonate core layer;

[0062] The core layer cobalt salt solution and the coating layer cobalt salt solution both contain Co and Al. The core layer cobalt salt solution may further contain Ni and / or Mn. The coating layer cobalt salt solution may further contain one or more elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba.

[0063] Wherein, the cobalt salt is selected from one or more of cobalt sulfate, cobalt chloride, and cobalt nitrate; the precipitant is selected from one or more of ammonium bicarbonate, ammonium carbonate, and sodium carbonate; and the base liquid is selected from one or more of ammonium bicarbonate, ammonium carbonate, and sodium carbonate;

[0064] The cobalt concentration in the cobalt salt solution is 85-125 g / L, the concentration of the precipitant solution is 180-220 g / L; the pH of the base solution is 7.5-8.8;

[0065] The pH during the reaction for preparing the cobalt carbonate core layer is 7.0-8.3, and the ammonium concentration is 10-60 g / L;

[0066] The pH during the reaction for preparing the cobalt carbonate coating layer is 6.5-8.0, and the ammonium concentration is 10-40 g / L;

[0067] The flow rate of the core layer cobalt salt solution is 1.5% / h-7.0% / h of the available volume of the reactor; the flow rate of the coating layer cobalt salt solution is 1.5% / h-3.5% / h of the available volume of the reactor.

[0068] The fourth aspect of the present application further provides a method for preparing cobalt tetroxide, which is obtained by sintering the above-mentioned cobalt carbonate.

[0069] The fifth aspect of the present application further provides a positive electrode material, which is lithium cobalt oxide obtained by calcining the above-mentioned cobalt trioxide and a lithium source;

[0070] Preferably, the molar ratio of the lithium source to the cobalt oxide is (1-1.05):1;

[0071] Preferably, the calcination temperature is 900° C. to 1200° C., and the calcination time is 20 to 30 hours.

[0072] In a sixth aspect, the present application further provides a lithium-ion battery, the raw materials of which include the above-mentioned positive electrode material.

[0073] Compared with the prior art, the advantages of this application include:

[0074] 1. The cobalt carbonate and cobalt oxide provided in this application include a core layer and a coating layer coated outside the core layer. By gradient-doping the entire cobalt oxide particle with Al, and with a higher Al doping amount in the core layer than in the coating layer, the crystal structure stability of the LCO material can be improved, thereby improving the cycle performance. For cobalt carbonate, the Al element exists in the form of amorphous aluminum hydroxide during the crystallization process. The lower aluminum content in the coating layer is conducive to controlling the hydrolysis of amorphous aluminum hydroxide during centrifugal washing; and the porosity and pore volume of the coating layer are lower than those of the core layer, which is conducive to inhibiting the hydrolysis of amorphous aluminum hydroxide in the core layer, thereby improving the uniformity of aluminum element distribution.

[0075] 2. The cobalt carbonate and cobalt oxide core layers provided in this application account for a very large volume share, and further adopt Ni and Mn element doping to improve the core functions of long battery life and cycle life, which are of general concern in the industry. When synthesizing cobalt carbonate, the Ksp values of Ni and Co elements are relatively similar, which can be better co-precipitated to improve uniformity. In cobalt carbonate and cobalt oxide, Ni replaces part of Co in the crystal lattice, which can improve capacity performance; doping with Mn and Ni can also convert the phase change into solid solution behavior, effectively inhibiting the O3 / H1-3 phase change of the LCO material at a voltage of 4.5V, inhibiting crystal expansion, improving the stability of the crystal structure, increasing the platform voltage, and improving the cycle performance. If the volume share of the core layer is too small, the improvement in cycle and capacity will not be obvious.

[0076] 3. The cobalt carbonate and cobalt oxide coating layers provided in this application are coated on the outside of the core layer. The coating layer is very thin and accounts for a very small proportion. The coating layer can be modified according to the customer's customized needs to achieve the differentiated needs of different customers. Specifically, by setting the number of coating layers and different doping elements in each layer, each coating layer can achieve its specific function. For example, La, Zr and other elements are added to the coating layer, which have a large ionic radius to form a lithium garnet (LLZO) solid phase layer, so that the LCO material has good ion mobility and electrochemical stability; doping with Y and Ti can stabilize the structure, inhibit phase change, and improve rate performance; Mg doping can form a continuous channel, improve ion transmission efficiency, and improve surface conductivity; doping with Sr can improve conductivity, reduce impedance, and improve stability; doping with Ca can stabilize the skeleton structure of the material; doping with Ba can enhance the structural stability of lithium cobalt oxide, etc. Because the volume of the coating layer accounts for a small proportion, it is necessary to increase the content of doping elements to improve the material-specific performance effect and improve the overall performance of LCO.

[0077] 4. This application controls the cobalt content in the core layer cobalt solution and the coating layer cobalt solution during the preparation of cobalt carbonate, thereby controlling the cobalt content in cobalt carbonate and cobalt tetroxide, so that the cobalt content in the product decreases layer by layer from the inside to the outside, which can reduce the surface Co 4+ content, reduce Co dissolution and improve safety performance.

[0078] 5. In this application, the more types of doping elements and the higher the doping amount of cobalt carbonate and cobalt tetroxide, the more difficult it is to uniformly dope the doping elements. This application improves the product structure design and preparation method of cobalt carbonate and cobalt tetroxide, separates the doping elements of the core layer and the coating layer according to the different functions to be achieved, and each layer of the coating layer has different types of doping elements, and the coating layer is designed to be very thin, which can minimize the problem of decreased capacity and cycle performance of the final LCO material due to uneven doping.

[0079] 6. In the preparation of cobalt carbonate, the flow rate of the core layer cobalt salt solution is controlled to increase with the increase of the material particle size, the flow rate of the precipitant solution is controlled to increase with the increase of the flow rate of the core layer cobalt salt solution, and the stirring speed of the reactor is controlled to decrease with the increase of the material particle size. The obtained cobalt carbonate particles, cobalt tetroxide, and lithium cobaltate have moderate overall porosity, specific surface area, and overall pore volume, good doping uniformity, and the corresponding lithium-ion battery has a high cycle retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0081] Figure 1This is a scanning electron microscope morphology result of the core layer of the cobalt carbonate particles in Example 1;

[0082] Figure 2 This is a scanning electron microscope morphology result of the cobalt carbonate particle coating layer of Example 1;

[0083] Figure 3 This is a scanning electron microscope morphology result of a cross section of the coating layer of the cobalt carbonate particles of Example 1;

[0084] Figure 4 This is a scanning electron microscope morphology result of cobalt tetroxide in Example 1;

[0085] Figure 5 This is a scanning electron microscope morphology result of the cobalt oxide cross section of Example 1;

[0086] Figure 6 and Figure 7 The following are the analysis results of Al and Ni components in the core layer microregion of cobalt tetroxide in Example 1;

[0087] Figures 8 to 10 The following are the analysis results of Zr, Y and Ti components in the micro-area of the cobalt tetroxide coating layer of Example 1;

[0088] Figure 11 This is a scanning electron microscope morphology result of the cobalt carbonate particles of Example 2;

[0089] Figure 12 This is a scanning electron microscope morphology result of the cross section of the cobalt carbonate particles in Example 2;

[0090] Figure 13 This is a scanning electron microscope morphology result of cobalt tetroxide in Example 2;

[0091] Figure 14 This is a scanning electron microscope morphology result of the cobalt oxide cross section of Example 2;

[0092] Figure 15 This is a diagram showing the Al composition analysis results of the core layer microregion of cobalt tetroxide in Example 2;

[0093] Figures 16 and 17 The following are the Zr and Ti component analysis results of the cobalt oxide coating layer in Example 2;

[0094] Figure 18 This is a scanning electron microscope morphology result of the cobalt carbonate particles of Example 3;

[0095] Figure 19 This is a scanning electron microscope morphology result of cobalt tetroxide in Example 3;

[0096] Figure 20 This is a scanning electron microscope morphology result of the cobalt oxide cross section of Example 3;

[0097] Figure 21 This is a scanning electron microscope morphology result of the cobalt carbonate particles of Example 4;

[0098] Figure 22 This is a scanning electron microscope morphology result of cobalt tetroxide in Example 4;

[0099] Figure 23 This is a scanning electron microscope morphology result of the cobalt oxide cross section of Example 4;

[0100] Figure 24 This is a scanning electron microscope morphology result of the cobalt carbonate particles of Example 5;

[0101] Figure 25 This is a scanning electron microscope morphology result of cobalt tetroxide in Example 5;

[0102] Figure 26 This is a scanning electron microscope morphology result of the cobalt carbonate particles of Comparative Example 1;

[0103] Figure 27 This is a scanning electron microscope morphology result of cobalt tetroxide in Comparative Example 1;

[0104] Figure 28 This is a scanning electron microscope morphology result of the cobalt oxide cross section of Comparative Example 1;

[0105] Figure 29 This is a scanning electron microscope morphology result of the cobalt carbonate particles of Comparative Example 2;

[0106] Figure 30 This is a scanning electron microscope morphology result of the cross section of the cobalt carbonate particles of Comparative Example 2;

[0107] Figure 31 This is a scanning electron microscope morphology result of cobalt tetroxide in comparative example 2;

[0108] Figure 32 This is a scanning electron microscope morphology result of the cobalt oxide cross section of Comparative Example 2;

[0109] Figure 33 Schematic diagram of the structure of cobalt carbonate and cobalt trioxide of this application;

[0110] Figure 34 Schematic diagram of the structure of cobalt carbonate and cobalt trioxide in Example 1. DETAILED DESCRIPTION

[0111] As used herein:

[0112] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0113] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0114] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0115] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0116] Example 1

[0117] Example 1 provides a cobalt oxide precursor having a core layer doped with Al: 0.85wt%, Ni: 1.2wt%, and a coating layer of 5 layers, wherein the molar ratio of the elements in each coating layer is close to the molar ratio of the metal elements in the coating layer cobalt solution during preparation, and are approximately n1: Co: Al: Zr = 0.95: 0.03: 0.02, n2: Co: Al: La = 0.94: 0.03: 0.03, n3: Co: Al: Y = 0.91: 0.03: 0.06, n4: Co: Al: Ti = 0.88: 0.03: 0.09, and n5: Co: Al: Mg = 0.67: 0.03: 0.30. The structural diagram of the cobalt oxide precursor is shown in FIG. Figure 34As shown. Among them, n1 is the first coating layer coated outside the core layer, n2 is the second coating layer coated outside the first coating layer, n3 is the third coating layer coated outside the second coating layer, n4 is the fourth coating layer coated outside the third coating layer, n5 is the fifth coating layer coated outside the fourth coating layer, and the same below.

[0118] The preparation process is as follows:

[0119] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which serves as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is Co:Ni:Al=1:0.017:0.026; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 190 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0120] 2. The prepared core layer cobalt salt solution and precipitant solution were simultaneously added to a reactor containing a base solution to carry out a reaction. The flow rate of the cobalt salt solution was gradually increased from 2.5% / h to 6.0% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, and the stirring speed was gradually reduced from 350 r / min to 150 r / min. During the reaction, the pH value was controlled at 7.0-7.4, and the ammonium concentration was controlled at 15-30 g / L until the particle size D50 grew to 20.5 μm.

[0121] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer sequence. The thickness of each coating layer was about 0.25 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the aluminum-doped cobalt carbonate of Example 1 was prepared.

[0122] The scanning electron microscope morphology of the core layer of the cobalt carbonate particles in Example 1 is shown in FIG. Figure 1 The scanning electron microscope morphology of the cobalt carbonate particle coating is shown in Figure 2 The scanning electron microscope morphology of the cross section is shown in Figure 3 .

[0123] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 840° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.5 cm to prepare the multinary doped cobalt tetroxide of Example 1.

[0124] The structural diagram of cobalt carbonate and cobalt trioxide in Example 1 is shown in FIG. Figure 34 The scanning electron microscope morphology of the cobalt oxide of Example 1 is shown in FIG. Figure 4 The scanning electron microscope morphology of the cross section is shown in Figure 5 The cobalt oxide of Example 1 was analyzed using an electron probe to analyze the Al and Ni components in the core layer of the particles. The results were as follows: Figure 6 and Figure 7 As shown, Ni and Al elements are evenly distributed; the cobalt tetroxide of Example 1 was analyzed using an electron probe to analyze the Zr, Y, and Ti components of the particle coating layer. The results are as follows: Figures 8 to 10 As shown, each doping element is evenly distributed in the doped cladding layer.

[0125] 5. The cobalt trioxide obtained in Example 1 and lithium carbonate were uniformly mixed at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 1.

[0126] Example 2

[0127] Example 2 provides a cobalt oxide precursor having a core layer doped with 0.85 wt% Al and 1.2 wt% Mn and five coating layers, wherein the molar ratio of the elements in each coating layer is close to the molar ratio of the metal elements in the cobalt solution of the coating layer during preparation, namely, n1: Co:Al:La = 0.94:0.03:0.03, n2: Co:Al:Zr = 0.92:0.03:0.04, n3: Co:Al:Y = 0.91:0.03:0.06, n4: Co:Al:Ti = 0.88:0.03:0.09, and n5: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0128] 1. Aluminum sulfate solution, cobalt sulfate solution, and manganese sulfate solution are mixed to form a cobalt salt solution doped with aluminum and manganese elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al:Mn=1:0.026:0.018; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.5 is prepared as a base solution.

[0129] 2. The prepared core layer cobalt salt solution and precipitant solution were simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the core layer cobalt salt solution was gradually increased from 2.7% / h to 6.1% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, and the stirring speed was gradually reduced from 380 r / min to 160 r / min. During the reaction, the pH value was controlled at 7.1-7.5, and the ammonium concentration was controlled at 18-33 g / L until the particle size D50 grew to 18.5 μm.

[0130] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.5% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in the order of the coating layers. The thickness of each coating layer was about 0.25 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.7-7.1, and the ammonium concentration was controlled at 12-25 g / L until the aluminum-doped cobalt carbonate of Example 2 was prepared.

[0131] The scanning electron microscope morphology of the cobalt carbonate particles of Example 2 is shown in FIG. Figure 11 The scanning electron microscope morphology of the cross section is shown in Figure 12 .

[0132] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 840° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.5 cm to prepare the multinary doped cobalt tetroxide of Example 2.

[0133] The scanning electron microscope morphology of the cobalt oxide of Example 2 is shown in FIG. Figure 13 The scanning electron microscope morphology of the cross section is shown in Figure 14 The Al composition of the core layer of the cobalt oxide in Example 2 was analyzed using an electron probe. The results are as follows: Figure 15 As shown, the Al element is evenly distributed; the cobalt oxide of Example 2 was analyzed using an electron probe to analyze the Zr and Ti components of the particle coating layer micro-area. The results are as follows: Figure 16-17 As shown, each doping element is evenly distributed in layers.

[0134] 5. The cobalt trioxide obtained in Example 2 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 2.

[0135] Example 3

[0136] Example 3 provides a cobalt oxide precursor having a core layer doped with 0.95 wt% Al and two coating layers, wherein the molar ratio of the elements in the coating layers is close to the molar ratio of the metal elements in the cobalt solution of the coating layers during preparation, namely, n1: Co:Al:La = 0.94:0.03:0.03, and n2: Co:Al:Zr = 0.90:0.03:0.07. The preparation process is as follows:

[0137] 1. Aluminum sulfate and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with aluminum element, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al = 1:0.029; the concentration of the coating layer cobalt salt solution is mixed and configured according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.0 is prepared as a base solution.

[0138] 2. The prepared core layer cobalt salt solution and precipitant solution were simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the core layer cobalt salt solution was gradually increased from 2.4% / h to 5.9% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, and the stirring speed was gradually reduced from 380 r / min to 180 r / min. During the reaction, the pH value was controlled at 7.1-7.5, and the ammonium concentration was controlled at 20-35 g / L until the particle size D50 grew to 19.0 μm.

[0139] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.6% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer order. The thickness of each coating layer was about 0.35 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.9-7.3, and the ammonium concentration was controlled at 12-27 g / L until the aluminum-doped cobalt carbonate of Example 3 was prepared.

[0140] The scanning electron microscope morphology of the cobalt carbonate particles of Example 3 is shown in FIG. Figure 18 .

[0141] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 830° C., a sintering time of 3.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.0 cm to prepare the multinary doped cobalt tetroxide of Example 3.

[0142] The scanning electron microscope morphology of the cobalt trioxide of Example 3 is shown in FIG. Figure 19 The scanning electron microscope morphology of the cross section is shown in Figure 20 .

[0143] 5. The cobalt trioxide obtained in Example 3 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 3.

[0144] Example 4

[0145] Example 4 provides a cobalt oxide precursor having a core layer doped with 0.95 wt% Al and two coating layers, wherein the molar ratio of the elements in the coating layers is close to the molar ratio of the metal elements in the cobalt solution of the coating layers during preparation, namely, n1: Co:Al:Ti = 0.87:0.03:0.10, and n2: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0146] 1. Aluminum sulfate and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with aluminum element, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al = 1:0.029; the concentration of the coating layer cobalt salt solution is mixed and configured according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0147] 2. The prepared core layer cobalt salt solution and precipitant solution were simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the core layer cobalt salt solution was gradually increased from 2.5% / h to 6% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, and the stirring speed was reduced from 380 r / min to 150 r / min. During the reaction, the pH value was controlled at 7.2-7.6, and the ammonium concentration was controlled at 24-39 g / L until the particle size D50 grew to 19.0 μm.

[0148] 3. The process was changed to reduce the flow rate of the cobalt salt solution to 2.4% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.5 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in the order of the coating layers. The thickness of each coating layer was about 0.45 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 6.8-7.2, and the ammonium concentration was controlled at 10-25 g / L until the doped cobalt carbonate of Example 4 was prepared.

[0149] The scanning electron microscope morphology of the cobalt carbonate particles of Example 4 is shown in FIG. Figure 21 .

[0150] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 780° C., a sintering time of 2.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 2.5 cm to prepare the multinary doped cobalt tetroxide of Example 4.

[0151] The scanning electron microscope morphology of the cobalt trioxide of Example 4 is shown in FIG. Figure 22 The scanning electron microscope morphology of the cross section is shown in Figure 23 .

[0152] 5. The cobalt trioxide obtained in Example 4 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 4.

[0153] Example 5

[0154] Example 5 provides a cobalt oxide precursor having a core layer doped with 1.2 wt% Ni and 0.95 wt% Al and five coating layers, wherein the molar ratio of the elements in each coating layer is close to the molar ratio of the metal elements in the cobalt solution of the coating layer during preparation, namely, n1: Co:Al:Zr = 0.95:0.03:0.02, n2: Co:Al:La = 0.94:0.03:0.03, n3: Co:Al:Y = 0.91:0.03:0.06, n4: Co:Al:Ti = 0.88:0.03:0.09, and n5: Co:Al:Mg = 0.67:0.03:0.30. The preparation process is as follows:

[0155] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with nickel and aluminum elements, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt, nickel, and aluminum elements in the solution is: Co:Ni:Al=1:0.017:0.029; the concentration of the coating layer cobalt salt solution is mixed according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 190 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0156] 2. The prepared cobalt salt solution and precipitant solution were simultaneously added to a reactor containing a base liquid to carry out a reaction. The flow rate of the cobalt salt solution was gradually increased from 2.5% / h to 6.2% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, and the stirring speed was gradually reduced from 350 r / min to 150 r / min. During the reaction, the pH value was controlled at 7.0-7.4, the ammonium concentration was controlled at 15-30 g / L, and the particle size D50 grew to 20.5 μm.

[0157] 6. The process was changed to reduce the flow rate of the cobalt salt solution to 2.7% / h of the available volume of the reactor, and the flow rate of the precipitant solution was 1.6 times the flow rate of the cobalt salt solution. The prepared coating layer cobalt salt solution was pumped in according to the coating layer order. The thickness of each coating layer was about 0.25 μm. After the particle size was reached, the next coating layer solution was replaced. During the reaction, the pH value was controlled at 7.3-7.5, and the ammonium concentration was controlled at 20-35 g / L until the aluminum-doped cobalt carbonate of Example 5 was prepared.

[0158] The scanning electron microscope morphology of the cobalt carbonate particles of Example 5 is shown in FIG. Figure 24 .

[0159] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 800° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.0 cm to prepare the multinary doped cobalt tetroxide of Example 5.

[0160] The scanning electron microscope morphology of the cobalt trioxide of Example 5 is shown in FIG. Figure 25 .

[0161] 5. The cobalt trioxide obtained in Example 5 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Example 5.

[0162] Comparative Example 1

[0163] Comparative Example 1 provides a cobalt oxide precursor having a core layer doped with 1.0 wt% Al and two coating layers, wherein the molar ratio of the elements in each coating layer is close to the molar ratio of the metal elements in the cobalt solution of the coating layer during preparation, namely, n1: Co: Al = 0.95:0.05, and n2: Co: Al = 0.97:0.03, respectively. The preparation process is as follows:

[0164] 1. Aluminum sulfate and cobalt sulfate solutions are mixed to form a cobalt salt solution doped with aluminum element, which is used as the core layer cobalt salt solution, wherein the mass concentration of cobalt ions is 100 g / L, and the molar ratio of cobalt and aluminum elements in the solution is: Co:Al = 1:0.03; the concentration of the coating layer cobalt salt solution is mixed and configured according to the molar ratio of each coating layer, wherein the mass concentration of cobalt salt in the coating layer cobalt salt solution is 100 g / L; and an ammonium bicarbonate solution with a mass concentration of 200 g / L is prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 is prepared as a base solution.

[0165] 2. The prepared core layer cobalt salt solution and precipitant solution were simultaneously added to the reactor containing the base liquid to carry out the reaction. The flow rate of the cobalt salt solution was gradually increased from 2.3% / h to 5.5% / h of the available volume of the reactor. The flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution. The stirring speed was gradually reduced from 380 r / min to 250 r / min, and the particle size D50 grew to 19.0 μm.

[0166] 3. Change the process, reduce the flow rate of the cobalt salt solution to 2.4% / h of the available volume of the reactor, the flow rate of the precipitant solution is 1.5 times the flow rate of the cobalt salt solution, and pump the configured coating layer cobalt salt solution in the order of the coating layer. The thickness of each coating layer is about 0.45 μm. After the particle size is reached, replace the next coating layer solution. During the reaction, the pH value is controlled at 6.8-7.2 and the ammonium concentration is controlled at 10-25 g / L until the doped cobalt carbonate of Comparative Example 1 is prepared.

[0167] The scanning electron microscope morphology of the cobalt carbonate particles of Comparative Example 1 is shown in FIG. Figure 26 .

[0168] 4. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 740° C., a sintering time of 2.0 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 2.5 cm to prepare the multinary doped cobalt tetroxide of Comparative Example 1.

[0169] The scanning electron microscope morphology of the cobalt trioxide of Comparative Example 1 is shown in Figure 27 The scanning electron microscope morphology of the cross section is shown in Figure 28 .

[0170] 5. The cobalt trioxide obtained in Comparative Example 1 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Comparative Example 1.

[0171] Comparative Example 2

[0172] Comparative Example 2 provides a cobalt tetroxide precursor doped with 1.2 wt% Ni and 0.85 wt% Al, which is not coated. The preparation process is as follows:

[0173] 1. Nickel sulfate, aluminum sulfate, and cobalt sulfate solutions were mixed to prepare a cobalt salt solution doped with nickel and aluminum elements, wherein the mass concentration of cobalt ions was 100 g / L and the molar ratio of cobalt, nickel, and aluminum elements in the solution was: Co:Ni:Al=1:0.017:0.026; and an ammonium bicarbonate solution with a mass concentration of 190 g / L was prepared as a precipitant solution; and an ammonium bicarbonate solution with a pH of 8.6 was prepared as a base solution.

[0174] 2. The prepared cobalt salt solution and precipitant solution were added simultaneously to the reactor containing the base liquid to carry out the reaction. The flow rate of the cobalt salt solution was 2.5% / h of the available volume of the reactor, the flow rate of the precipitant solution was twice the flow rate of the cobalt salt solution, the stirring speed was reduced from 350 r / min to 150 r / min, and the particle size D50 grew to 20.5 μm.

[0175] The scanning electron microscope morphology of the cobalt carbonate particles of Comparative Example 2 is shown in FIG. Figure 29 The scanning electron microscope morphology of the cross section is shown in Figure 30 .

[0176] 3. After centrifugal washing, the cobalt carbonate was sintered at a sintering temperature of 750° C., a sintering time of 2.5 h, a rotary kiln tube rotation frequency of 0.8 r / min, and a material layer thickness of 3.5 cm to prepare the multinary doped cobalt tetroxide of Comparative Example 2.

[0177] The scanning electron microscope morphology of the cobalt oxide of Comparative Example 2 is shown in FIG. Figure 31 The scanning electron microscope morphology of the cross section is shown in Figure 32 .from Figure 32 A honeycomb structure can be seen in the figure, which is caused by uneven aluminum doping.

[0178] 4. The cobalt trioxide obtained in Comparative Example 2 was mixed evenly with lithium carbonate at a Li / Me molar ratio of 1.05:1, and calcined at 1000° C. for 20 h to prepare the lithium cobalt oxide positive electrode material of Comparative Example 2.

[0179] The indicators of the cobalt carbonate of each embodiment and comparative example are shown in Table 1.

[0180] Table 1 Indexes of cobalt carbonate in various embodiments and comparative examples

[0181]

[0182]

[0183] The indicators of the cobalt tetroxide of each embodiment and comparative example are shown in Table 2, wherein Examples 1 to 4 and Comparative Example 1 are cobalt tetroxide with different types of doping elements and doping contents, respectively. The sintering process of Example 5 is different from that of Example 1, and its pore volume is larger; Comparative Example 2 is not coated with a coating layer, and its overall porosity and overall pore volume are lower, and the particle size is smaller.

[0184] Table 2 Indices of cobalt trioxide in various embodiments and comparative examples

[0185]

[0186]

[0187] Test example

[0188] The positive electrode materials of the above-mentioned embodiments and comparative examples were respectively dissolved in NMP solvent with conductive carbon black and polyvinylidene fluoride in a mass ratio of 85:10:5 under vacuum conditions to prepare a positive electrode slurry with a weight solid content of 80%. Positive electrode discs were then prepared by coating, drying, and punching. A lithium battery was then prepared in the order of positive electrode shell-positive electrode sheet-diaphragm-negative electrode sheet-stainless steel sheet-spring sheet-negative electrode shell. The electrolyte was 1 mol / LLiPF6 / EC:DMC (volume ratio of 1:1) with 10% (volume fraction) fluoroethylene carbonate (FEC) added. The diaphragm was a polypropylene microporous membrane. Batteries of Examples 1 to 5 and Comparative Examples 1 to 2 were prepared respectively. The battery performance of each embodiment and comparative example is shown in Table 3.

[0189] Table 3 Battery performance indicators of various embodiments and comparative examples

[0190]

[0191]

[0192] According to Table 1-3, compared with Comparative Examples 1-2, the batteries prepared in Examples 1-5 have both good discharge capacity and cycle performance, and have better 2C / 0.2C rate performance. Specifically:

[0193] 1. Compared with Example 1, the core layer of the cobalt tetroxide prepared in Example 2 is doped with manganese instead of nickel, and the capacity of the lithium ion battery prepared therefrom is slightly lower, but the cycle life is higher;

[0194] 2. Compared with Example 1, the cobalt oxide coating layers prepared in Examples 3 and 4 have fewer doping elements, forming a specific modified layer, and the core layer is not doped with Ni. The capacity and cycle retention rate of the lithium ion batteries prepared therefrom are slightly lower than those in Example 1, but are improved compared to Comparative Example 2.

[0195] 3. Compared with Examples 3 and 4, the cobalt trioxide prepared in Example 5 has an increased number of coating layers and a specific type of doping element. The coating layer plays a gain role, so the lithium ion battery prepared in Example 5 has a better cycle retention rate. In addition, the core layer of the material in Example 5 is doped with Ni to increase the discharge capacity of the material, eliminating the influence of the number of coating layers and the doping element on the capacity. Therefore, the capacity of the lithium ion battery prepared therefrom is equivalent to that of Examples 3 and 4.

[0196] 4. Compared with Example 1, the cobalt tetroxide prepared in Example 5 has a higher Al doping amount. The addition of Al element can stabilize the crystal structure, and the lithium ion battery prepared therefrom has an improved cycle retention rate. However, the excessive addition of Al element has a certain effect on the capacity, so the discharge capacity is slightly lower.

[0197] 5. Compared with Examples 1-5, the cobalt trioxide prepared in Comparative Example 1 is provided with a coating layer, but the cobalt content of the coating layer increases layer by layer and no other doping elements except Al are added for modification. 4+ Dissolution increased, and the stirring speed did not decrease with the growth of particle size, and a certain speed was continuously maintained. The overall porosity of the obtained cobalt carbonate particles was low, the specific surface area was low, and the overall pore volume was low. The corresponding cycle retention rate of the lithium-ion battery was deteriorated. The capacity and cycle retention rate of the battery were poor compared with those of Examples 1-5. However, the setting of the coating layer improved the stability of the material surface structure. Therefore, the capacity and cycle retention rate of Comparative Example 1 were higher than those of Comparative Example 2, but lower than those of each embodiment.

[0198] 6. Compared with Examples 1-5, the cobalt trioxide prepared in Comparative Example 2 has no coating layer, and the doping elements in the core layer are unevenly distributed, resulting in a decrease in the capacity and cycle retention rate of the corresponding lithium-ion battery.

[0199] 7. Compared with Comparative Examples 1 and 2, the cobalt oxide-derived cathode materials prepared in Examples 1 to 5 all exhibited 2C / 0.2C rate performance exceeding 97.9% at 3.6-4.55V, significantly improving rate performance. The rate performance of Examples 1, 2, and 3 all exceeded 98%, demonstrating that the doping of elements in the coating layer of the material achieved the desired effect. Example 3 employed La and Zr doping, which significantly improved ion mobility, i.e., rate performance. Example 4 employed Ti and Mg doping, which formed continuous channels, enhancing ion transport efficiency and rate performance.

[0200] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0201] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form distinct embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A cobalt trioxide, characterized in that: The cobalt trioxide comprises a core layer and a coating layer coated outside the core layer; the core layer and the coating layer are both doped with Al, and the Al doping content of the core layer is higher than the Al doping content of the coating layer; The cobalt content of the cobalt trioxide decreases layer by layer from the core layer to the coating layer; The cobalt trioxide coating layer is 2 to 5 layers.

2. The cobalt trioxide according to claim 1, characterized in that The cobalt trioxide satisfies at least one of the following conditions A to E: A. The ratio of the mass of Al doped in the core layer of the cobalt oxide to the total mass of metal in the core layer of the cobalt oxide is: 0.40-1.20wt%; B. The ratio of the mass of Al doped in the cobalt oxide coating layer to the total metal mass in the cobalt oxide is: 0.02-0.40wt%; C. the ratio of the molar amount of cobalt in the outermost layer of the cobalt oxide coating layer to the molar amount of the total metal in the outermost layer of the cobalt oxide coating layer is ≤70 mol; D. The diameter of the core layer of the cobalt trioxide is 5.0-18.0 μm; E. The thickness of a single layer of the cobalt trioxide coating layer is 0.10-1.0 μm.

3. The cobalt trioxide according to claim 1 or 2, characterized in that The cobalt trioxide satisfies at least one of the following conditions I to L: I. The core layer of the cobalt trioxide further includes Ni and / or Mn; J. When condition I is met, the ratio of the mass of Ni and Mn doped in the core layer of the cobalt oxide to the total metal mass in the core layer of the cobalt oxide is independently 0.10-3.00 wt %; K. The cobalt oxide coating layer further includes one or more doping elements selected from the group consisting of Mg, Ti, La, Zr, Y, Ca, Sr, and Ba; When the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further comprises one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further comprises one or more of Mg, Zr, Ti, and Sr; When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, the inner layer of the coating layer further comprises one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer further comprises one or more of La, Zr, Y, Ti, and Sr; and the outer layer of the coating layer further comprises one or more of Mg, Zr, Ti, and Sr; L. When condition K is met, the ratio of the mass of other doping elements except Al in the cobalt oxide coating layer to the total metal mass in the cobalt oxide is independently 0.01-0.40 wt%.

4. The cobalt trioxide according to claim 3, characterized in that The cobalt trioxide satisfies at least one of the following conditions M to Q: M. The porosity of the core layer of the cobalt oxide is 5.5-9.5%, and the overall porosity of the cobalt oxide is 4.5-7.5%; N. The pore volume of the core layer of the cobalt trioxide is 0.004~0.015cm 3 / g, the overall pore volume of the cobalt trioxide is 0.002~0.080cm 3 / g; O. the D50 of the cobalt trioxide is 5.5 to 23.0 μm; P. The tap density of the cobalt trioxide is 2.0~3.0g / cm 3 ; Q. The specific surface area of the cobalt trioxide is 2.0~15m 2 / g.

5. A cobalt carbonate, characterized in that The cobalt carbonate comprises a core layer and a coating layer coated outside the core layer; the core layer and the coating layer of the cobalt carbonate are both doped with Al, and the Al doping content of the core layer of the cobalt carbonate is higher than the Al doping content of the coating layer of the cobalt carbonate; The cobalt content of the cobalt carbonate decreases layer by layer from the core layer of the cobalt carbonate to the coating layer of the cobalt carbonate; The coating layer of the cobalt carbonate is 2 to 5 layers.

6. Cobalt carbonate according to claim 5, characterized in that The cobalt carbonate satisfies at least one of the following conditions a to i: a. The ratio of the mass of the doped Al in the core layer of the cobalt carbonate to the total mass of the metal in the core layer of the cobalt carbonate is: 0.26~0.80wt%; b. The ratio of the mass of the doped Al in the cobalt carbonate coating to the total mass of the metal in the cobalt carbonate is: 0.01~0.27wt%; c. the ratio of the molar amount of cobalt in the outermost layer of the cobalt carbonate coating layer to the total molar amount of metal in the outermost layer of the cobalt carbonate coating layer is ≤70 mol; d. The diameter of the core layer of the cobalt carbonate is 8.0~23.0μm; e. The cobalt carbonate coating layer has a single layer thickness of 0.15 to 1.5 μm; f. The core layer of the cobalt carbonate further comprises Ni and / or Mn; g. When condition f is met, the ratio of the mass of Ni and Mn doped in the core layer of cobalt carbonate to the total mass of metal in the core layer of cobalt carbonate is independently: 0.07~2.00wt%; h. The cobalt carbonate coating further comprises one or more doping elements of Mg, Ti, La, Zr, Y, Ca, Sr, or Ba; When the coating layer is two layers, the coating layer is divided into an inner layer and an outer layer, the inner layer of the coating layer further comprises one or more of Zr, La, Ca, Ba, Y, Ti, and Sr; the outer layer of the coating layer further comprises one or more of Mg, Zr, Ti, and Sr; When the coating layer has 3-5 layers, the coating layer is divided into an inner layer, an intermediate layer and an outer layer, the inner layer and the outer layer are respectively 1 layer, the inner layer of the coating layer further comprises one or more of Zr, La, Ca, and Ba; the intermediate layer of the coating layer further comprises one or more of La, Zr, Y, Ti, and Sr; and the outer layer of the coating layer further comprises one or more of Mg, Zr, Ti, and Sr; i. When condition h is met, the ratio of the mass of the other doping elements in the cobalt carbonate coating layer except Al to the total mass of the metal in the cobalt carbonate is independently: 0.01~0.30wt%.

7. Cobalt carbonate according to claim 6, characterized in that The cobalt carbonate satisfies at least one of the following conditions m~q: m. The porosity of the core layer of the cobalt carbonate is 15 to 25%, and the overall porosity of the cobalt carbonate is 14 to 25%; n. The pore volume of the core layer of the cobalt carbonate is 0.08~0.30 cm 3 / g, and the overall pore volume of the cobalt carbonate is 0.05~0.25cm 3 / g; o. The D50 of the cobalt carbonate is 8.7~30.0μm; p. The specific surface area of the cobalt carbonate is 50~150m 2 / g; q. The tap density of the cobalt carbonate is 1.5~2.0 g / cm 3 .

8. A method for preparing cobalt carbonate according to any one of claims 5 to 7, characterized in that: include: adding a core layer cobalt salt solution and a precipitant solution into a reactor containing a base liquid to react, wherein the flow rate of the core layer cobalt salt solution increases with the increase of the material particle size, the flow rate of the precipitant solution increases with the increase of the flow rate of the core layer cobalt salt solution, and the stirring speed of the reactor decreases with the increase of the material particle size, and the reaction is continued until the particle size D50 is 8.0-23.0 μm, thereby obtaining a cobalt carbonate core layer; Sequentially adding a coating layer cobalt salt solution and a precipitant solution into a reactor containing the cobalt carbonate core layer to react until the growth of each coating layer is completed to obtain cobalt carbonate; The core layer cobalt salt solution and the coating layer cobalt salt solution both contain Co and Al.

9. A method for preparing cobalt trioxide, characterized in that: The cobalt carbonate is obtained by sintering the cobalt carbonate prepared by the cobalt carbonate according to any one of claims 5 to 7 or the method for preparing cobalt carbonate according to claim 8.

10. A positive electrode material, characterized in that Lithium cobaltate obtained by calcining the cobalt trioxide according to any one of claims 1 to 4 with a lithium source.

11. The positive electrode material according to claim 10, characterized in that The molar ratio of the lithium source to the cobalt tetroxide is (1-1.05):

1.

12. The positive electrode material according to claim 10, characterized in that The calcination temperature is 900° C. to 1200° C., and the calcination time is 20 to 30 hours.

13. A lithium ion battery, characterized in that: The raw materials include the positive electrode material according to any one of claims 10 to 12.

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