Modified lithium cobalt oxide positive electrode material and preparation method thereof

Abstract

The invention provides a modified lithium cobalt oxide positive electrode material and a preparation method thereof.The modified lithium cobalt oxide positive electrode material is of a core-shell structure and comprises a magnesium-aluminum-doped lithium cobalt oxide core material serving as the core-shell structure and a coating layer formed on the surface of the magnesium-aluminum-doped lithium cobalt oxide core material, and the coating layer is lithium titanium aluminum phosphate, lithium niobate and lithium phosphate; the chemical formula of the lithium titanium aluminum phosphate is Li < 1 + x > Al < x > Ti < 1 + 1-x > (PO4) 3, the chemical formula of the lithium niobate is Li3NbO4, the weight of the coating layer accounts for 0.2-2% of the weight of the modified lithium cobalt oxide positive electrode material, the weight ratio of the lithium titanium aluminum phosphate to the lithium niobate in the coating layer is 1: (0.4-2), and the chemical formula of the magnesium-aluminum doped lithium cobalt oxide core material is LiCo < 1-a-b-c > Mg Al Nb < c > O2. The modified lithium cobalt oxide positive electrode material provided by the 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 particularly to a modified lithium cobaltate cathode material and a preparation method thereof. Background Art

[0002] In today's society, lithium-ion batteries have advantages such as small size, high energy density, and long life compared to traditional batteries in the past. Currently, they are widely used in various aspects, including drones, electronic cigarettes, electric vehicles, etc. For lithium cobaltate cathode materials in high-voltage application scenarios, higher requirements are put forward for the structural support of the materials. In high-rate application scenarios, it is usually desired to improve the ionic conductivity by doping elements with large ionic radii to meet the high-rate performance requirements. Existing technologies use coating modification to extend their cycle retention rate. However, generally speaking, in high-voltage applications, improving the performance of lithium cobaltate cathode materials by doping elements with large ionic radii still needs to be improved. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the existing technologies and provide a modified lithium cobaltate cathode material and a preparation method thereof.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: a modified lithium cobaltate cathode material, the modified lithium cobaltate cathode material has a core-shell structure, including a magnesium-aluminum doped lithium cobaltate core material as the core-shell structure and a coating layer formed on the surface of the magnesium-aluminum doped lithium cobaltate 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, where 0.2 ≤ x ≤ 0.5. The chemical formula of lithium niobate is Li3NbO4. The weight of the coating layer accounts for 0.2% - 2% of the weight of the modified lithium cobaltate cathode material. The weight ratio of lithium aluminum titanium phosphate to lithium niobate in the coating layer is 1:(0.4 - 2). The chemical formula of the magnesium-aluminum doped lithium cobaltate 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 modified lithium cobalt oxide cathode material has a core-shell structure. Magnesium, aluminum, and niobium are simultaneously doped into the lithium cobalt oxide core material. Meanwhile, a coating layer of lithium aluminum titanate 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 highly dense and high-entropy coating material, which can further improve the structural stability. The remaining reaction product, lithium phosphate, is coated on the particle surface. The above modified lithium cobalt oxide cathode material can better inhibit the overflow of oxygen elements, thereby reducing the possibility of swelling, and has a more stable interface. In the coating layer formed by lithium aluminum titanate phosphate, lithium niobate, and lithium phosphate of the modified lithium cobalt oxide cathode material, a mixed coating layer with a decreasing concentration gradient of lithium niobate is formed from the material surface inward. The highly dense and high-entropy coating co-coating will also improve the diffusion rate and stability of lithium ions in the material, thus having better rate performance. The mixed coating layer with a decreasing concentration gradient of lithium niobate is a highly dense and high-entropy coating material, which reduces the degree of erosion during contact with the electrolyte and reduces the internal stress generated during the charge and discharge process of the material to improve the cycle stability of the material. During the charge and discharge process, lithium ion compounds will also be formed, improving the lithium ion diffusion rate on the material surface, and further improving the performance expression of the material under high rate and high voltage. Therefore, the stability under high voltage application is improved, and the lithium ion diffusion rate of the modified lithium cobalt oxide cathode material enables it to have better performance at high rates.

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

[0007] When the weight ratio of lithium aluminum titanate phosphate to lithium niobate in the coating layer is 1:(0.4 - 1.2), the modified lithium cobalt oxide cathode material has more excellent capacity and cycle performance under high voltage.

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

[0009] When the weight of the coating layer accounts for 0.5% - 1.5% of the weight of the modified lithium cobalt oxide cathode material, the modified lithium cobalt oxide cathode material has more excellent capacity and cycle performance under high voltage.

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

[0011] Preferably, the preparation method of the modified lithium cobalt oxide cathode material includes the following steps: (1) Mix magnesium oxide, aluminum hydroxide, niobium source, cobalt tetroxide, and lithium carbonate, and sinter at 950 - 1000 °C in an oxygen-containing atmosphere for 20 - 25 hours to form a first-fired material; (2) Control the particle size D50 of the first-fired material to be < 7 μm, and sinter 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 the modified lithium cobalt oxide cathode material.

[0012] The present invention provides a method for preparing the modified lithium cobalt oxide cathode material described in any one of the above, and the method includes the following steps:

[0013] (1) Mix magnesium oxide, aluminum hydroxide, niobium source, cobalt source, and lithium source, and sinter at 950-1000 °C in an oxygen-containing atmosphere for 20-25 hours to form a first-fired material; (2) Control the particle size D50 of the first-fired material < 7 μm and sinter 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 the modified lithium cobalt oxide cathode material.

[0014] Preferably, in step (1), the lithium source is lithium carbonate, the cobalt source is cobalt tetroxide, mix lithium carbonate and the cobalt source in a high-speed mixer at a frequency of 35-45 Hz for 25-45 min, the mixing temperature does not exceed 70 °C, and then add magnesium oxide, aluminum hydroxide, and the niobium source to mix again.

[0015] Preferably, after sintering in step (1), it is naturally cooled, and after sintering in step (2), it is cooled at 3 °C - 5 °C / min.

[0016] The beneficial effects of the present invention are as follows: The present invention provides a modified lithium cobalt oxide cathode material and a preparation method thereof. The modified lithium cobalt oxide cathode material of the present invention has a core-shell structure. Through synchronous doping of lithium cobalt oxide core material with magnesium, aluminum, and niobium, a coating layer of lithium aluminum titanate 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 highly dense and high-entropy coating material, which can further improve the structural stability; the remaining reaction product lithium phosphate is coated on the particle surface. The above-mentioned modified lithium cobalt oxide cathode material can better inhibit the overflow of oxygen elements, thereby reducing the possibility of swelling, and has a more stable interface. In the coating layer formed by lithium aluminum titanate phosphate, lithium niobate, and lithium phosphate of the modified lithium cobalt oxide cathode material, a mixed coating layer with a decreasing lithium niobate concentration gradient is formed from the material surface to the inside. The highly dense and high-entropy coating co-coating will also improve the diffusion rate and stability of lithium ions in the material, thereby having better rate performance. The mixed coating layer with a decreasing lithium niobate concentration gradient is a highly dense and high-entropy coating material, which reduces the degree of erosion during contact with the electrolyte, reduces the internal stress generated during the charge and discharge process of the material, so as to improve the cycle stability of the material; during the charge and discharge process, lithium ion compounds will also be formed, improving the lithium ion diffusion rate on the material surface, and further improving the performance expression of the material at high rates and high voltages; thereby improving its stability under high-voltage applications. The lithium ion diffusion rate of the modified lithium cobalt oxide cathode material enables it to have better performance at high rates. Description of the Drawings

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

[0018] Figure 2 It is the scanning electron microscope image of the modified lithium cobalt oxide cathode material of Comparative Example 2 of the present invention. Specific embodiments

[0019] To better illustrate the purpose, technical solution 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 cathode material of an embodiment of the present invention, the modified lithium cobalt oxide cathode material has a core-shell structure, including 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. The coating layer is lithium aluminum titanate phosphate, lithium niobate and lithium phosphate. The chemical formula of lithium aluminum titanate 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 cathode material. The weight ratio of lithium aluminum titanate phosphate to lithium niobate in the coating layer is 1:1.2. 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 cathode material in this example includes the steps:

[0023] The present invention provides the preparation method of the modified lithium cobalt oxide cathode material described in any one of the above. The method includes the following steps:

[0024] (1) Mix lithium carbonate and cobalt source in a high-speed mixer at a frequency of 40 Hz for 35 min. The mixing temperature does not exceed 70 °C. Add magnesium oxide as the magnesium source, aluminum hydroxide as the aluminum source and niobium pentoxide and mix again. Sinter in air at 980 °C for 20 hours to form a first-fired material, and cool naturally. The lithium source is lithium carbonate, and the cobalt source is cobalt tetroxide;

[0025] (2) Control the particle size D50 of the first-fired material < 7 μm and sinter with the aluminum source, titanium hydrogen phosphate and niobium pentoxide in air at 700 °C for 18 hours, and then cool at 4 °C / min to obtain the modified lithium cobalt oxide cathode material.

[0026] Example 2

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

[0028] Example 3

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

[0030] Example 4

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

[0032] Example 5

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

[0034] Example 6

[0035] As a modified lithium cobaltate cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that the weight of the coating layer accounts for 0.2% of the weight of the modified lithium cobaltate cathode material.

[0036] Example 7

[0037] As a modified lithium cobaltate cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that the weight of the coating layer accounts for 0.5% of the weight of the modified lithium cobaltate cathode material.

[0038] Example 8

[0039] As a modified lithium cobaltate cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that the weight of the coating layer accounts for 1.2% of the weight of the modified lithium cobaltate cathode material.

[0040] Example 9

[0041] As a modified lithium cobaltate cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 1 is that the weight of the coating layer accounts for 1.8% of the weight of the modified lithium cobaltate cathode material.

[0042] The amounts of the coating layers in Examples 1 to 9 are all achieved by adjusting the raw material ratios during the preparation process.

[0043] Comparative Example 1

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

[0045] Comparative Example 2

[0046] As a modified lithium cobaltate cathode 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 titanium aluminum phosphate in the coating layer, and the corresponding mass content is supplemented by lithium niobate.

[0047] Comparative Example 3

[0048] As a modified lithium cobaltate cathode 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 phosphate in the coating layer, and the corresponding mass content is supplemented by lithium niobate and lithium titanium aluminum phosphate in proportion.

[0049] Comparative Example 4

[0050] As a modified lithium cobaltate cathode material of the 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 cobaltate cathode material of the 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 cobaltate cathode material of the 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 cobaltate cathode material of the comparative example of the present invention, the only difference between this comparative example and Example 1 is that:

[0057] The preparation method of the modified lithium cobaltate cathode material includes the following steps:

[0058] (1) Mix lithium carbonate and cobalt source in a high-speed mixer at a frequency of 40 Hz for 35 min, the mixing temperature does not exceed 70 °C, add magnesium oxide as the magnesium source, aluminum hydroxide as the aluminum source and niobium pentoxide and mix again, sinter in air at 980 °C for 20 hours to form a first-fired material, and cool naturally. The lithium source is lithium carbonate, and the cobalt source is cobalt tetroxide;

[0059] (2) Control the particle size D50 of the first-fired material < 7 μm and sinter with the aluminum source and titanium hydrogen phosphate in air at 700 °C for 18 hours, and then cool at 4 °C / min to obtain the lithium titanium aluminum phosphate-coated lithium cobaltate cathode material;

[0060] (3) The lithium cobaltate cathode material coated with lithium titanium phosphate obtained in step (2) and niobium pentoxide are sintered in air at 700 °C for 18 hours, and then cooled at 4 °C / min to obtain the modified lithium cobaltate cathode material.

[0061] Experimental method

[0062] I. Material characterization

[0063] Figure 1 This is the scanning electron microscope image of the modified lithium cobaltate cathode material of Example 1 of the present invention.

[0064] Figure 2 This is the scanning electron microscope image of the modified lithium cobaltate cathode material of Comparative Example 2 of the present invention.

[0065] II. Battery performance of the modified lithium cobaltate cathode material

[0066] The rate performance and cycle stability of the modified lithium cobaltate cathode materials of Examples 1-9 and Comparative Examples 1-7 under high voltage were tested, and the test methods are as follows:

[0067] The cathode material was prepared into a button cell. The test conditions were as follows: at 4.4 V, the discharge specific capacity was tested by constant current charge and discharge at 0.2 C for horizontal comparison. The rate performance was tested by charging and discharging at different charge rates to test the discharge specific capacity (the rates included 0.5 C, 1 C, and 5 C);

[0068] In addition, in the subsequent charge and discharge cycles, charge and discharge were carried out at a rate of 1 C for one hundred cycles to test the cycle retention rate of the battery;

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

[0070] Table 1 Performance of the modified lithium cobaltate cathode material at high rate and high voltage

[0071]

[0072]

[0073] As can be seen from Table 1, the modified lithium cobaltate cathode material of the example has better performance expression at high rate and high voltage compared with the modified lithium cobaltate cathode material of the comparative example; it can improve its stability under high voltage applications. The lithium ion diffusion rate of the modified lithium cobaltate cathode 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 rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced 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, and 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, niobium source, cobalt tetroxide and lithium carbonate, and sintering 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 sintered material 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.

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, niobium source, cobalt source and lithium source, and sintering 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 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.

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, aluminum hydroxide and niobium source are added and mixed again.

8. The method for preparing the modified lithium cobalt oxide positive electrode material according to claim 6, characterized in that: Step (1) is followed by natural cooling after sintering, and step (2) is followed by cooling at 3°C ​​to 5°C / min after sintering.

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