A modified lithium cobalt oxide positive electrode material and preparation method thereof

Abstract

The present invention provides a modified lithium cobalt oxide positive electrode material and a preparation method thereof. The modified lithium cobalt oxide positive electrode material is a core-shell structure, comprising a magnesium aluminum doped lithium cobalt oxide core material as the core-shell structure and a coating layer formed on the surface of the magnesium aluminum doped lithium cobalt oxide core material, wherein the coating layer is lithium aluminum titanium phosphate, lithium niobate and lithium phosphate. The chemical formula of lithium aluminum titanium phosphate is Li 1+x Al x Ti 1+1‑x (PO4)3, the chemical formula of lithium niobate is Li3NbO4, the weight of the coating layer accounts for 0.2% to 2% of the weight of the modified lithium cobalt oxide positive electrode material, the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1: (0.4 to 2), and the chemical formula of the magnesium aluminum doped lithium cobalt oxide core material is LiCo 1‑a‑b‑ c Mg a Al b Nb c The modified lithium cobalt oxide positive electrode material of the present invention has better battery performance at high temperature, high voltage and high rate.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a modified lithium cobalt oxide positive electrode material and a preparation method thereof. Background Art

[0002] In today's society, lithium-ion batteries offer advantages over traditional batteries, such as small size, high energy density, and long life. They are currently widely used in various fields, including drones, e-cigarettes, and electric vehicles. High-voltage applications of lithium cobalt oxide cathode materials place higher demands on the structural support of the material. In high-rate applications, it is generally desirable to increase ionic conductivity by doping with elements with large ionic radii to achieve high-rate performance requirements. Existing technologies use coating modifications to extend the cycle retention rate. However, overall, improving the performance of lithium cobalt oxide cathode materials by doping with elements with large ionic radii under high-voltage applications still needs to be improved. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a modified lithium cobalt oxide positive electrode material and a preparation method thereof.

[0004] To achieve the above object, the technical solution adopted by the present invention is: a modified lithium cobalt oxide positive electrode material, the modified lithium cobalt oxide positive electrode material is a core-shell structure, including a magnesium aluminum doped lithium cobalt oxide core material as a core-shell structure and a coating layer formed on the surface of the magnesium aluminum doped lithium cobalt oxide core material, the coating layer is lithium aluminum titanium phosphate, lithium niobate and lithium phosphate, the chemical formula of lithium aluminum titanium phosphate is Li 1+x Al x Ti 1+1-x (PO4)3, wherein 0.2≤x≤0.5, the chemical formula of lithium niobate is Li3NbO4, the weight of the coating layer accounts for 0.2% to 2% of the weight of the modified lithium cobalt oxide positive electrode material, the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:(0.4 to 2), and the chemical formula of the magnesium aluminum doped lithium cobalt oxide core material is LiCo 1-a-b-c Mg a Al b Nb c O2, 0.001≤a≤0.003, 0.001≤b≤0.002, 0.001≤c≤0.003.

[0005] The above-mentioned modified lithium cobalt oxide positive electrode material is a core-shell structure. The lithium cobalt oxide core material is simultaneously doped with magnesium, aluminum and niobium. At the same time, a coating layer of lithium aluminum titanium phosphate, lithium niobate and lithium phosphate is formed on the surface of the magnesium-aluminum doped lithium cobalt oxide core material. The coating forms a high-density high-entropy coating material, which can further improve the structural stability; the residual reaction product lithium phosphate is coated on the surface of the particles. The above-mentioned modified lithium cobalt oxide positive electrode material better inhibits the overflow of oxygen elements and thus reduces the possibility of flatulence, and has a more stable interface. The lithium phosphate and lithium cobalt oxide particles in the coating layer form a continuous structure. In the coating layer formed by lithium aluminum titanium phosphate, lithium niobate and lithium phosphate of the modified lithium cobalt oxide positive electrode material, a mixed coating layer with a decreasing lithium niobate concentration gradient is formed from the surface of the material to the inside. The high-density high-entropy coating and co-coating will also increase the diffusion rate and stability of lithium ions in the material, thereby having better rate performance. The mixed coating layer with a reduced lithium niobate concentration gradient is a high-density, high-entropy coating material, which reduces the degree of erosion during contact with the electrolyte and reduces the internal stress generated by the material during the charge and discharge process, thereby improving the material's cycle stability; lithium ion compounds will also be formed during the charge and discharge process, increasing the lithium ion diffusion rate on the material surface, thereby improving the material's performance expression at high rates and high voltages; thereby improving its stability under high voltage applications, and modifying the lithium ion diffusion rate of the lithium cobalt oxide positive electrode material to enable it to have better performance at high rates.

[0006] Preferably, the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:(0.4-1.2).

[0007] When the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:(0.4~1.2), the modified lithium cobalt oxide positive electrode material has better capacity and cycle performance at high voltage.

[0008] Preferably, the weight of the coating layer accounts for 0.5% to 1.5% of the weight of the modified lithium cobalt oxide positive electrode material.

[0009] When the weight of the coating layer accounts for 0.5% to 1.5% of the weight of the modified lithium cobalt oxide positive electrode material, the modified lithium cobalt oxide positive electrode material has better capacity and cycle performance at high voltage.

[0010] Preferably, the particle size D50 of the magnesium-aluminum-doped lithium cobalt oxide core material is less than 7 μm.

[0011] Preferably, the preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps: (1) mixing magnesium oxide, aluminum hydroxide, niobium source, cobalt tetroxide, and lithium carbonate, and sintering the mixture at 950-1000° C. in an oxygen-containing atmosphere for 20-25 hours to form a sintered material; (2) controlling the particle size D50 of the sintered material to be less than 7 μm, and sintering the mixture with aluminum source, titanium hydrogen phosphate, and niobium pentoxide at 700-750° C. in an oxygen-containing atmosphere for 18-20 hours to obtain a modified lithium cobalt oxide positive electrode material.

[0012] The present invention provides a method for preparing any of the above-mentioned modified lithium cobalt oxide positive electrode materials, the method comprising the following steps:

[0013] (1) Mixing magnesium oxide, aluminum hydroxide, a niobium source, a cobalt source, and a lithium source, and sintering the mixture at 950-1000° C. in an oxygen-containing atmosphere for 20-25 hours to form a sintered material; (2) Controlling the particle size D50 of the sintered material to be less than 7 μm, and sintering the mixture with an aluminum source, titanium hydrogen phosphate, and niobium pentoxide at 700-750° C. in an oxygen-containing atmosphere for 18-20 hours to obtain a modified lithium cobalt oxide positive electrode material.

[0014] Preferably, in step (1), the lithium source is lithium carbonate and the cobalt source is cobalt tetroxide. The lithium carbonate and the cobalt source are mixed in a high-speed mixer at a frequency of 35 to 45 Hz for 25 to 45 minutes, and the mixing temperature does not exceed 70° C. Magnesium oxide and aluminum hydroxide are added and mixed again with the niobium source.

[0015] Preferably, step (1) is followed by natural cooling after sintering, and step (2) is followed by cooling at a rate of 3°C to 5°C / min after sintering.

[0016] The beneficial effects of the present invention are as follows: the present invention provides a modified lithium cobalt oxide positive electrode material and a preparation method thereof, the modified lithium cobalt oxide positive electrode material of the present invention is a core-shell structure, the lithium cobalt oxide core material is simultaneously doped with magnesium, aluminum and niobium, and a coating layer of lithium aluminum titanium phosphate, lithium niobate and lithium phosphate is formed on the surface of the magnesium-aluminum doped lithium cobalt oxide core material, the coating forms a high-density high-entropy coating material, which can further improve the structural stability; the reaction residual product lithium phosphate is coated on the surface of the particles, the above-mentioned modified lithium cobalt oxide positive electrode material better inhibits the overflow of oxygen elements and thus reduces the possibility of flatulence, has a more stable interface, the lithium phosphate and the lithium cobalt oxide particles in the coating layer form a continuous structure, and in the coating layer formed by the lithium aluminum titanium phosphate, lithium niobate and lithium phosphate of the modified lithium cobalt oxide positive electrode material, a mixed coating layer with a decreasing lithium niobate concentration gradient is formed from the surface of the material to the inside, and the high-density high-entropy coating co-coating can also improve the diffusion rate and stability of lithium ions in the material, thereby having better rate performance. The mixed coating layer with a reduced lithium niobate concentration gradient is a high-density, high-entropy coating material, which reduces the degree of erosion during contact with the electrolyte and reduces the internal stress generated by the material during the charge and discharge process, thereby improving the material's cycle stability; lithium ion compounds will also be formed during the charge and discharge process, increasing the lithium ion diffusion rate on the material surface, thereby improving the material's performance expression at high rates and high voltages; thereby improving its stability under high voltage applications, and modifying the lithium ion diffusion rate of the lithium cobalt oxide positive electrode material to enable it to have better performance at high rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a scanning electron microscope image of the modified lithium cobalt oxide positive electrode material of Example 1 of the present invention.

[0018] Figure 2 This is a scanning electron microscope image of the modified lithium cobalt oxide positive electrode material of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0019] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0020] Example 1

[0021] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the modified lithium cobalt oxide positive electrode material is a core-shell structure, including a magnesium aluminum doped lithium cobalt oxide core material as a core-shell structure and a coating layer formed on the surface of the magnesium aluminum doped lithium cobalt oxide core material, the coating layer is lithium aluminum titanium phosphate, lithium niobate and lithium phosphate, and the chemical formula of lithium aluminum titanium phosphate is Li 1+x Al x Ti 1+1-x (PO4)3, where x = 0.3, the chemical formula of lithium niobate is Li3NbO4, the weight of the coating layer accounts for 0.8% of the weight of the modified lithium cobalt oxide positive electrode material, the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:1.2, and the chemical formula of the magnesium aluminum doped lithium cobalt oxide core material is LiCo 1-a-b-c Mg a Al b Nb c O2, a=0.002, b≤0.015, c=0.002.

[0022] The preparation method of the modified lithium cobalt oxide positive electrode material of this embodiment includes the following steps:

[0023] The present invention provides a method for preparing any of the above-mentioned modified lithium cobalt oxide positive electrode materials, the method comprising the following steps:

[0024] (1) lithium carbonate and a cobalt source are mixed in a high-speed mixer at a frequency of 40 Hz for 35 minutes, with the mixing temperature not exceeding 70° C., magnesium oxide is added as a magnesium source, aluminum hydroxide as an aluminum source, and niobium pentoxide is mixed again, and sintered in air at 980° C. for 20 hours to form a single-fired material, which is then naturally cooled. The lithium source is lithium carbonate, and the cobalt source is cobalt tetroxide;

[0025] (2) The particle size D50 of the sintered material was controlled to be less than 7 μm, and the material was sintered with aluminum source, titanium hydrogen phosphate, and niobium pentoxide at 700°C in air for 18 hours, and then cooled at 4°C / min to obtain a modified lithium cobalt oxide positive electrode material.

[0026] Example 2

[0027] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:0.4.

[0028] Example 3

[0029] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:0.8.

[0030] Example 4

[0031] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:1.5.

[0032] Example 5

[0033] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:2.

[0034] Example 6

[0035] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight of the coating layer accounts for 0.2% of the weight of the modified lithium cobalt oxide positive electrode material.

[0036] Example 7

[0037] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight of the coating layer accounts for 0.5% of the weight of the modified lithium cobalt oxide positive electrode material.

[0038] Example 8

[0039] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight of the coating layer accounts for 1.2% of the weight of the modified lithium cobalt oxide positive electrode material.

[0040] Example 9

[0041] As a modified lithium cobalt oxide positive electrode material of an embodiment of the present invention, the only difference between this embodiment and Example 1 is that the weight of the coating layer accounts for 1.8% of the weight of the modified lithium cobalt oxide positive electrode material.

[0042] The amount of the coating layer in Examples 1 to 9 was achieved by adjusting the ratio of raw materials during the preparation process.

[0043] Comparative Example 1

[0044] As a modified lithium cobalt oxide positive electrode material of the comparative example of the present invention, the only difference between this comparative example and Example 1 is that there is no lithium niobate in the coating layer, and the corresponding mass content is supplemented by lithium aluminum titanium phosphate.

[0045] Comparative Example 2

[0046] As a modified lithium cobalt oxide positive electrode material of the comparative example of the present invention, the only difference between this comparative example and Example 1 is that there is no lithium aluminum titanium phosphate in the coating layer, and the corresponding mass content is supplemented by lithium niobate.

[0047] Comparative Example 3

[0048] As a modified lithium cobalt oxide positive electrode material of a comparative example of the present invention, the only difference between this comparative example and Example 1 is that there is no lithium phosphate in the coating layer, and the corresponding mass content is supplemented by lithium niobate and lithium aluminum titanium phosphate in proportion.

[0049] Comparative Example 4

[0050] As a modified lithium cobalt oxide positive electrode material of a comparative example of the present invention, the only difference between this comparative example and Example 1 is that the core material is not doped with magnesium, and the corresponding mass content is supplemented by niobium and aluminum.

[0051] Comparative Example 5

[0052] As a modified lithium cobalt oxide positive electrode material of a comparative example of the present invention, the only difference between this comparative example and Example 1 is that the core material is not doped with aluminum, and the corresponding mass content is supplemented by niobium and magnesium.

[0053] Comparative Example 6

[0054] As a modified lithium cobalt oxide positive electrode material of a comparative example of the present invention, the only difference between this comparative example and Example 1 is that the core material is not doped with niobium, and the corresponding mass content is supplemented by magnesium and aluminum.

[0055] Comparative Example 7

[0056] As a modified lithium cobalt oxide positive electrode material of the comparative example of the present invention, the only difference between this comparative example and Example 1 is:

[0057] The preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps:

[0058] (1) lithium carbonate and a cobalt source are mixed in a high-speed mixer at a frequency of 40 Hz for 35 minutes, with the mixing temperature not exceeding 70° C., magnesium oxide is added as a magnesium source, aluminum hydroxide as an aluminum source, and niobium pentoxide is mixed again, and sintered in air at 980° C. for 20 hours to form a single-fired material, which is then naturally cooled. The lithium source is lithium carbonate, and the cobalt source is cobalt tetroxide;

[0059] (2) controlling the particle size D50 of the sintered material to be less than 7 μm, sintering it with an aluminum source and titanium hydrogen phosphate at 700° C. in air for 18 hours and then cooling it at 4° C. / min to obtain a lithium aluminum titanium phosphate-coated lithium cobalt oxide positive electrode material;

[0060] (3) The lithium aluminum titanium phosphate coated lithium cobalt oxide positive electrode material obtained in step (2) was sintered with niobium pentoxide in air at 700° C. for 18 hours and then cooled at 4° C. / min to obtain a modified lithium cobalt oxide positive electrode material.

[0061] Experimental methods

[0062] 1. Material Characterization

[0063] Figure 1 This is a scanning electron microscope image of the modified lithium cobalt oxide positive electrode material of Example 1 of the present invention.

[0064] Figure 2 This is a scanning electron microscope image of the modified lithium cobalt oxide positive electrode material of Comparative Example 2 of the present invention.

[0065] 2. Battery performance of modified lithium cobalt oxide cathode materials

[0066] The rate performance and cycle stability of the modified lithium cobalt oxide positive electrode materials of Examples 1-9 and Comparative Examples 1-7 under high voltage were tested. The test method is as follows:

[0067] The positive electrode material was prepared into a button cell. The test conditions were 4.4V, and the discharge specific capacity was tested at 0.2C for horizontal comparison. The test rate performance was tested at different charge and discharge rates (rates included 0.5C, 1C and 5C).

[0068] In addition, in the subsequent charge and discharge cycles, 100 cycles of charge and discharge are performed at a rate of 1C to test the cycle retention rate of the battery;

[0069] The experimental results are shown in Table 1:

[0070] Table 1 Performance of modified lithium cobalt oxide cathode materials at high rate and high voltage

[0071]

[0072]

[0073] As can be seen from Table 1, the modified lithium cobalt oxide modified lithium cobalt oxide positive electrode material of the embodiment has better performance expression at high rate and high voltage than the modified lithium cobalt oxide modified lithium cobalt oxide positive electrode material of the comparative example; it can improve its stability under high voltage application, and the lithium ion diffusion rate of the modified lithium cobalt oxide positive electrode material enables it to have better performance at high voltage and high rate.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A modified lithium cobalt oxide positive electrode material, characterized in that: The modified lithium cobalt oxide positive electrode material is a core-shell structure, including a magnesium aluminum doped lithium cobalt oxide core material as a core-shell structure and a coating layer formed on the surface of the magnesium aluminum doped lithium cobalt oxide core material, wherein the coating layer is lithium aluminum titanium phosphate, lithium niobate and lithium phosphate. The chemical formula of lithium aluminum titanium phosphate is Li 1+x Al x Ti 1+1-x (PO4)3, wherein 0.2≤x≤0.5, the chemical formula of lithium niobate is Li3NbO4, the weight of the coating layer accounts for 0.2% to 2% of the weight of the modified lithium cobalt oxide positive electrode material, the weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:(0.4 to 2), and the chemical formula of the magnesium aluminum doped lithium cobalt oxide core material is LiCo 1-a-b-c Mg a Al b Nb c O2, 0.001≤a≤0.003, 0.001≤b≤0.002, 0.001≤c≤0.

003.

2. The modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that The weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:(0.4-1.2).

3. The modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The weight of the coating layer accounts for 0.5% to 1.5% of the weight of the modified lithium cobalt oxide positive electrode material.

4. The modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that The particle size D50 of the magnesium-aluminum-doped lithium cobalt oxide core material is less than 7 μm.

5. The modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps: (1) mixing magnesium oxide, aluminum hydroxide, a niobium source, cobalt trioxide, and lithium carbonate, and sintering the mixture at 950-1000° C. in an oxygen-containing atmosphere for 20-25 hours to form a sintered material; (2) controlling the particle size D50 of the sintered material to be less than 7 μm, and sintering the mixture with an aluminum source, titanium hydrogen phosphate, and niobium pentoxide at 700-750° C. in an oxygen-containing atmosphere for 18-20 hours to obtain a modified lithium cobalt oxide positive electrode material.

6. A method for preparing the modified lithium cobalt oxide positive electrode material according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: (1) Mixing magnesium oxide, aluminum hydroxide, a niobium source, a cobalt source, and a lithium source, and sintering the mixture at 950-1000° C. in an oxygen-containing atmosphere for 20-25 hours to form a sintered material; (2) Controlling the particle size D50 of the sintered material to be less than 7 μm, and sintering the mixture with an aluminum source, titanium hydrogen phosphate, and niobium pentoxide at 700-750° C. in an oxygen-containing atmosphere for 18-20 hours to obtain a modified lithium cobalt oxide positive electrode material.

7. The method for preparing the modified lithium cobalt oxide positive electrode material according to claim 6, characterized in that: In step (1), the lithium source is lithium carbonate and the cobalt source is cobalt tetroxide. The lithium carbonate and the cobalt source are mixed in a high-speed mixer at a frequency of 35 to 45 Hz for 25 to 45 minutes, and the mixing temperature does not exceed 70° C. Magnesium oxide and aluminum hydroxide are added and mixed again with the niobium source.

8. The method for preparing the modified lithium cobalt oxide positive electrode material according to claim 6, characterized in that: After sintering in step (1), the mixture is naturally cooled. After sintering in step (2), the mixture is cooled at a rate of 3°C to 5°C / min.

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