A modified lithium cobalt oxide material, its preparation method and application

Abstract

The present invention provides a modified lithium cobalt oxide material, a preparation method thereof and an application. The preparation method comprises the following steps: (1) mixing a lithium cobalt oxide material and a solvent to obtain a suspension, stirring and heating, and then testing a first pH value and a first zeta potential φ1; (2) adding an alkali solution and a coating salt solution into the suspension in a co-current manner, and controlling a second pH value of the system to carry out a reaction; (3) aging and then measuring a second zeta potential φ2 to obtain the modified lithium cobalt oxide material. The present application provides a general preparation method for coating various elements, reduces the erosion of the coating solution to the material, and improves the bonding degree between the material and the coating layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a modified lithium cobaltate material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its advantages such as high working voltage, stable charge-discharge structure, high specific energy, good cycle stability, and environmental friendliness, lithium cobaltate materials are widely used in products such as smart phones, tablet computers, and drones. With the development of electronic products, people's requirements for the battery performance of lithium cobaltate are also getting higher and higher. In order to improve the cycle performance and specific capacity of lithium cobaltate materials, common methods include ion doping and element coating.

[0003] Element coating usually improves the stability of the material and the ion transport performance through coating with oxides, phosphides, fluorides, etc. The traditional coating method is usually to obtain by high-temperature calcination after solid mixing lithium cobaltate and the coating material in proportion. This method is simple and easy to operate, but it also has the disadvantages of uneven coating and loose coating. Therefore, a large number of studies have proposed new wet coating processes:

[0004] CN109994711A discloses a preparation method of a doped and coated lithium cobaltate cathode material. By dissolving magnesium acetate anhydrous, aluminum isopropoxide, and tetraethyl orthosilicate in an anhydrous ethanol solution and mixing with the lithium cobaltate material in a liquid phase, the effect of uniformly coating oxides of Al, Mg, and Si on the surface of lithium cobaltate can be achieved, thereby improving the electrochemical performance of the lithium cobaltate material, but it does not propose how to control the effectiveness of the coating.

[0005] CN113346066A discloses a phosphate-coated lithium cobaltate cathode material and a preparation method thereof. Through the sol-gel method, first form a milky white gel of the coating material with a positive Zeta potential, and then add the lithium cobaltate cathode material with a negative Zeta potential. Utilize the positive and negative charge attraction between small particles in the liquid phase to adsorb on the material surface, and finally obtain a lithium cobaltate battery cathode material coated with strontium aluminum tantalum zirconium phosphate fast ion conductor by stirring and heating to evaporate to dryness. It utilizes the principle that the potential of the coating material is opposite to that of lithium cobaltate to improve the effectiveness of the coating, but the requirement that the potential of the coating mixture is positive limits the types of coatings; at the same time, the addition method of adding the lithium cobaltate suspension to the coating solution further limits the pH value (cobalt begins to have a slight dissolution phenomenon in a solution with a pH lower than 3) and types of the coating solution. Summary of the Invention

[0006] The purpose of the present invention is to provide a modified lithium cobaltate material, a preparation method thereof, and an application thereof. This application provides a universal preparation method for coating with different types of elements, reducing the erosion of the coating solution to the material while improving the bonding degree between the material and the coating layer.

[0007] To achieve the object of this invention, the following technical solutions are adopted in this invention:

[0008] In the first aspect, this invention provides a preparation method of a modified lithium cobaltate material, and the preparation method includes the following steps:

[0009] (1) Mix the lithium cobaltate material and a solvent to obtain a suspension, stir and heat it up, and then measure the first pH and the first zeta potential.

[0010] (2) Add an alkali solution and a coating salt solution into the suspension in a parallel flow manner, and control the second pH of the system to react.

[0011] (3) Measure the second zeta potential after aging. Obtain the modified lithium cobaltate material.

[0012] By adopting the parallel flow coating method, this invention forms uniform core-coated particles. Especially for salt solutions with relatively strong acidity such as magnesium chloride and titanyl sulfate solutions, it can avoid the erosion of cobalt when the acid solution is added to the lithium cobaltate suspension and prevent the destruction of the intrinsic structure of the lithium cobaltate material. At the same time, due to the presence of residual alkali in the lithium cobaltate material, by controlling the range of its initial pH1 and the pH2 value during stable coating feeding, it can not only achieve the effect of completely precipitating the coating elements, but also promote the combination of the coated particles on the surface of the lithium cobaltate by utilizing the differences in surface potential.

[0013] Preferably, the solid-liquid ratio of the suspension in step (1) is 1:(8 - 80), for example: 1:8, 1:10, 1:20, 1:50 or 1:80, etc.

[0014] Preferably, the temperature for heating up in step (1) is 50 - 80°C, for example: 50°C, 55°C, 60°C, 70°C or 80°C, etc.

[0015] Preferably, the first pH is 10.5 - 12, for example: 10.5, 10.8, 11, 11.5 or 12, etc.

[0016] Preferably, the first zeta potential range is -200 - -20 mV, for example: -200 mV, -150 mV, -100 mV, -50 mV or -20 mV, etc.

[0017] Preferably, the concentration of the alkali solution in step (2) is 0.1 - 0.5 mol / L, for example: 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc.

[0018] Preferably, the solute of the coating salt solution includes any one or a combination of at least two of aluminum salt, magnesium salt, cobalt salt, manganese salt, zirconium salt, tantalum salt, strontium salt, silicate or titanium salt.

[0019] Preferably, the concentration of the coating salt solution is 0.001 - 0.1 mol / L, for example: 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.08 mol / L or 0.1 mol / L, etc.

[0020] Preferably, the second pH in step (2) is 8 - 9.5, for example: 8, 8.2, 8.5, 9 or 9.5, etc.

[0021] Preferably, the aging time in step (3) is 0.5 - 1 h, for example: 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h or 1 h, etc.

[0022] Preferably, the second zeta potential in step (3) is -20 - 0 mV, for example: -20 mV, -15 mV, -10 mV, -5 mV or 0 mV, etc.

[0023] Preferably, after measuring the second zeta potential the suspension is washed until the conductivity is qualified and then dried to obtain the modified lithium cobaltate material.

[0024] In a second aspect, the present invention provides a modified lithium cobaltate material, which is prepared by the method as described in the first aspect.

[0025] In a third aspect, the present invention provides a positive electrode plate, which comprises the modified lithium cobaltate material as described in the second aspect.

[0026] In a fourth aspect, the present invention provides a lithium ion battery, which comprises the positive electrode plate as described in the third aspect.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) By adopting a co-current coating method, the present invention forms uniform core-coated particles, which can avoid the erosion of cobalt when the acid solution is added to the lithium cobaltate suspension and damage the intrinsic structure of the lithium cobaltate material. At the same time, due to the existence of residual alkali in the lithium cobaltate material, its initial pH1 is between 10.5 - 12. By stabilizing the pH2 value range during the coating feed at 8 - 9.5, it can not only achieve the effect of completely precipitating the coating elements, but also promote the combination of the coated particles on the surface of the lithium cobaltate by utilizing the differences in surface potential.

[0029] (2) The specific capacity of the modified lithium cobaltate material prepared by the method of the present invention can reach more than 189.6 mAh / g, the cycle retention rate can reach more than 92.5% after 50 cycles, and the rate performance of 2C / 0.5C can reach more than 91.9%. Through the effective coating of the lithium cobaltate material, its electrical properties are significantly improved, the specific capacity is increased, and at the same time, the cycle performance and rate performance are enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the SEM image of the modified lithium cobaltate material prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0032] Example 1

[0033] This example provides a modified lithium cobaltate material, and the preparation method of the modified lithium cobaltate material is as follows:

[0034] (1) Add 200 g of lithium cobaltate material into 4 L of water to form a uniform suspension with a solid-liquid ratio of 1:20; ② Under stirring conditions, heat the lithium cobaltate suspension to 80 °C, and detect its pH value as 10.6 through an industrial electrode. After reaching 80 °C, take the suspension for zeta potential test. It is -45.6 mV;

[0035] (2) Prepare 500 mL of 0.006 mol / L titanium oxysulfate solution and 0.2 mol / L sodium hydroxide solution. Pump the titanium oxysulfate solution into the lithium cobaltate suspension at a rate of 5 mL / min, and at the same time adjust the flow rate of the sodium hydroxide solution and keep the pH at 9.5 unchanged;

[0036] (3) After the addition of the titanium oxysulfate solution is completed, continue to stir and age for 0.5 h. Take the coated lithium cobaltate suspension for zeta potential test. It is -6.9 mV. After washing the suspension until the conductivity is qualified, dry it to obtain the modified lithium cobaltate material. The SEM image of the modified lithium cobaltate material is as Figure 1 shown.

[0037] Example 2

[0038] This example provides a modified lithium cobaltate material, and the preparation method of the modified lithium cobaltate material is as follows:

[0039] (1) Add 200 g of lithium cobaltate material to 4 L of water to form a uniform suspension with a solid-liquid ratio of 1:30; ② Under stirring conditions, heat the lithium cobaltate suspension to 73 °C and measure its pH value to be 11 using an industrial electrode. After reaching 73 °C, take the suspension for zeta potential measurement. It was -55.6 mV;

[0040] (2) Prepare 500 mL of 0.05 mol / L magnesium sulfate solution and 0.3 mol / L sodium hydroxide solution. Pump the magnesium sulfate solution into the lithium cobaltate suspension at a rate of 5 mL / min, and at the same time adjust the flow rate of the sodium hydroxide solution and keep the pH at 9 unchanged.

[0041] (3) After the addition of the magnesium sulfate solution is completed, continue stirring and aging for 0.8 h. Take the coated lithium cobaltate suspension for zeta potential measurement. It was -8.2 mV. Wash the suspension until the conductivity is qualified and then dry it to obtain the modified lithium cobaltate material.

[0042] Example 3

[0043] The difference between this example and Example 1 is only that the first pH is 10, and other conditions and parameters are exactly the same as those in Example 1.

[0044] Example 4

[0045] The difference between this example and Example 1 is only that the first pH is 12.5, and other conditions and parameters are exactly the same as those in Example 1.

[0046] Example 5

[0047] The difference between this example and Example 1 is only that the second pH is 7.5, and other conditions and parameters are exactly the same as those in Example 1.

[0048] Example 6

[0049] The difference between this example and Example 1 is only that the second pH is 10, and other conditions and parameters are exactly the same as those in Example 1.

[0050] Example 7

[0051] The difference between this example and Example 1 is only that the first zeta potential is -250 mV, and other conditions and parameters are exactly the same as those in Example 1.

[0052] Example 8

[0053] The difference between this example and Example 1 is only that the first zeta potential is -10 mV, and other conditions and parameters are exactly the same as those in Example 1.

[0054] Example 9

[0055] The difference between this example and Example 1 is only that the second zeta potential is -30 mV, and other conditions and parameters are exactly the same as those in Example 1.

[0056] Performance test:

[0057] Mix the modified lithium cobaltate materials, PVDF, and conductive carbon black prepared in Examples 1-9 in a mass ratio of 95.4:2.5:2.1, add NMP, and stir to make a slurry. Coat the slurry on aluminum foil and dry it at 120 °C to make a positive electrode sheet; assemble it with a negative electrode sheet, a separator, an electrolyte, etc. into a 063048-type battery. Test the performance of the battery, and the test results are shown in Table 1:

[0058] Table 1

[0059] Capacity retention rate after 50 cycles (%) Rate performance at 2C / 0.5C (%) Specific capacity (mAh / g) Example 1 92.8 91.9 189.6 Example 2 92.5 92.5 190.8 Example 3 91.2 91.8 188.5 Example 4 92.1 91.5 186.9 Example 5 90.6 91.5 189.2 Example 6 92.5 90.5 186.2 Example 7 92.6 90.2 185.3 Example 8 90.4 91.1 187.7 Example 9 91.2 92.3 188.8

[0060] It can be seen from Table 1 that from Examples 1-2, the specific capacity of the modified lithium cobaltate material prepared by the method of the present invention can reach more than 189.6 mAh / g, the cycle retention rate after 50 cycles can reach more than 92.5%, and the 2C / 0.5C rate performance can reach more than 91.9%.

[0061] By comparing Example 1 with Examples 3-4, it can be obtained that during the preparation process of the modified lithium cobaltate material of the present invention, the first pH will affect the performance of the prepared modified lithium cobaltate material. Controlling the first pH at 10.5-12 results in better performance of the prepared lithium cobaltate material. If the first pH is too low, the cycle performance of lithium cobaltate will decrease significantly. If the first pH is too high, the specific capacity of lithium cobaltate will decrease significantly and the rate performance will deteriorate.

[0062] By comparing Example 1 with Examples 5-6, it can be obtained that during the preparation process of the modified lithium cobaltate material of the present invention, the second pH will affect the performance of the prepared modified lithium cobaltate material. Controlling the second pH at 8-9.5 results in better performance of the prepared lithium cobaltate material. If the second pH is too low, the cycle performance of lithium cobaltate will decrease significantly. If the second pH is too high, the specific capacity of lithium cobaltate will decrease significantly and the rate performance will deteriorate.

[0063] By comparing Example 1 with Examples 7-8, it can be obtained that during the preparation process of the modified lithium cobaltate material of the present invention, the first zeta potential will affect the performance of the prepared modified lithium cobaltate material. Controlling the first zeta potential at -200 to -20 mV results in better performance of the prepared lithium cobaltate material. If the first zeta potential is too low, the specific capacity of lithium cobaltate will decrease significantly and the rate performance will deteriorate. If the first zeta potential is too high, the cycle performance of lithium cobaltate will decrease significantly.

[0064] It can be obtained by comparing Example 1 with Examples 9-10 that during the preparation process of the modified lithium cobaltate material of the present invention, the second zeta potential will affect the performance of the prepared modified lithium cobaltate material. Controlling the second zeta potential within -20 to 0 mV results in better performance of the lithium cobaltate material. If the second zeta potential is too low, the cycling performance of the lithium cobaltate will decrease significantly.

[0065] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a modified lithium cobalt oxide material, characterized in that, The preparation method comprises the following steps: (1) Mix the lithium cobaltate material and the solvent to obtain a suspension, stir and heat it up, and then measure the first pH and the first zeta potential φ1; the first pH is 10.5 - 12; the range of the first zeta potential φ1 is -200 - -20 mV; (2) Add the alkali solution and the coating salt solution to the suspension in a parallel flow manner, and control the second pH of the system to react; the second pH is 8 - 9.5; (3) After aging, measure the second zeta potential φ2 to obtain the modified lithium cobaltate material; the second zeta potential φ2 is -20 - 0 mV.

2. The preparation method according to claim 1, wherein, The solid-liquid ratio of the suspension in step (1) is 1:(8 - 80).

3. The preparation method according to claim 1, characterized in that The temperature of heating up in step (1) is 50 - 80 °C.

4. The preparation method according to claim 1, characterized in that, The concentration of the alkali solution in step (2) is 0.1 - 0.5 mol / L.

5. The preparation method according to claim 1, characterized in that, The solute of the coating salt solution includes any one or a combination of at least two of aluminum salt, magnesium salt, cobalt salt, manganese salt, zirconium salt, tantalum salt, strontium salt, silicate or titanium salt.

6. The preparation method according to claim 1, characterized in that, The concentration of the coating salt solution is 0.001 - 0.1 mol / L.

7. The preparation method according to claim 1, characterized in that, The aging time in step (3) is 0.5 - 1 h.

8. The preparation method according to claim 1, characterized in that, After measuring the second zeta potential φ2, wash the suspension until the conductivity is qualified and then dry it to obtain the modified lithium cobaltate material.

9. A modified lithium cobaltate material, characterized in that, The modified lithium cobaltate material is prepared by the method according to any one of claims 1 - 8.

10. A positive electrode plate, characterized in that, The positive electrode sheet comprises the modified lithium cobaltate material according to claim 9.

11. A lithium-ion battery, characterized in that, The lithium ion battery comprises the positive electrode sheet according to claim 10.

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