Positive electrode material, preparation method thereof, positive electrode plate and lithium ion battery

Abstract

The embodiment of the invention relates to a positive electrode material, a preparation method thereof, a positive electrode plate and a lithium ion battery. The preparation method comprises the following steps: mixing a lithium source and a manganese source to obtain a mixed material; under the air condition, calcining the mixed material to obtain a lithium manganate precursor; the preparation method comprises the following steps: uniformly mixing an organic carbon source and a hydrogen peroxide solution according to a certain mass ratio under an ultrasonic condition to obtain a pre-oxidized organic carbon source mixed solution; and adding the lithium manganate precursor into the pre-oxidized organic carbon source mixed solution, carrying out uniform ultrasonic treatment to obtain a suspension, and drying the suspension at a low temperature of 180-250 DEG C to obtain the carbon-coated lithium manganate positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and in particular to a positive electrode material and a preparation method thereof, as well as a positive electrode plate and a lithium ion battery. Background Art

[0002] Lithium secondary batteries (including aqueous and organic systems) composed of spinel lithium manganese oxide positive electrode materials have the characteristics of high voltage, good rate performance, low cost, high safety, non-toxicity, and environmental friendliness. However, lithium-ion secondary batteries based on lithium manganese oxide decay seriously during the cycle process, especially under high state of charge (SOC) and high temperature conditions (>40°C), which is mainly caused by the Jahn-Teller effect and manganese ion dissolution. After dissolving from the positive electrode, manganese ions will migrate to the negative electrode for deposition, continuously catalyzing side reactions at the negative electrode, continuously consuming electrolyte and active lithium ions, resulting in rapid decay of battery capacity, increased battery impedance, and severe decay of power performance.

[0003] In response to these problems, the industry has proposed some solutions, such as: doping and coating the positive electrode, using new electrolyte additives, and coating the negative electrode surface with a physical barrier functional layer to alleviate the dissolution of manganese. However, the above methods will reduce the material capacity and increase the impedance to a certain extent, affecting the low temperature and rate performance of the material. The carbon coating method can physically restrain the dissolution of manganese ions and hinder the migration of manganese ions to the negative electrode, but the carbon coating of lithium manganese oxide is more difficult. The traditional carbon coating method cannot be applied to lithium manganese oxide because carbon will reduce lithium manganese oxide at high temperatures, causing structural damage. Summary of the invention

[0004] The purpose of the present invention is to provide a positive electrode material and a preparation method thereof, a positive electrode plate and a lithium ion battery. By using a pre-oxidized organic carbon source to achieve low-temperature coating of lithium manganate, a carbon-coated lithium manganate positive electrode material is obtained, which can improve the rate performance and cycle stability of the lithium manganate material.

[0005] To this end, in a first aspect, an embodiment of the present invention provides a method for preparing a positive electrode material, the preparation method comprising:

[0006] The lithium source and the manganese source are mixed to obtain a mixed material;

[0007] calcining the mixed material under air conditions to obtain a lithium manganate precursor;

[0008] The organic carbon source and the hydrogen peroxide solution are mixed uniformly under ultrasonic conditions in a certain mass ratio to obtain a pre-oxidized organic carbon source mixed solution;

[0009] The lithium manganate precursor is added to the pre-oxidized organic carbon source mixed solution, ultrasonically homogenized to obtain a suspension, and the suspension is low-temperature dried at 180° C.-250° C. to obtain a carbon-coated lithium manganate positive electrode material.

[0010] Preferably, the mixing of the lithium source and the manganese source specifically comprises:

[0011] Mix appropriate amounts of lithium source and manganese source according to the molar ratio using a high-speed mixer; or,

[0012] An excess lithium source and an appropriate amount of manganese source are mixed in a high-speed mixer according to a molar ratio; wherein the excess of the lithium source according to the molar ratio does not exceed 11%.

[0013] More preferably, the mixing speed of the high-speed mixer is 400 to 2300 r / min, and the mixing time is 5 to 40 min.

[0014] Preferably, the lithium source includes lithium hydroxide and / or lithium carbonate;

[0015] The manganese source includes one of α-MnO2, β-MnO2, R-MnO2, Mn2O3 or Mn3O4; the particle size of the manganese source is 3 to 14 μm.

[0016] Preferably, the organic carbon source comprises maltitol and / or triethanolamine;

[0017] The mass ratio of the organic carbon source to the hydrogen peroxide solution is 1:1.5-1:2;

[0018] The concentration of the hydrogen peroxide is 5%-20%.

[0019] Preferably, the heating rate of the calcination is 3 to 6° C. / min; the sintering temperature of the calcination is 650 to 850° C.; and the holding time of the calcination is 10 to 20 hours.

[0020] Preferably, the mass ratio of the organic carbon source to the lithium manganate precursor is 1:9 to 4:6;

[0021] The ultrasonic mixing is carried out in an ultrasonic pulverizer, the ultrasonic power is 110-180W, and the ultrasonic time is 0.5-2h.

[0022] In a second aspect, an embodiment of the present invention provides a carbon-coated lithium manganese oxide positive electrode material prepared by the preparation method described in the first aspect above, wherein the lithium manganese oxide positive electrode material is a spinel phase, and the particle size of the carbon-coated lithium manganese oxide positive electrode material is 8 to 14 μm.

[0023] In a third aspect, an embodiment of the present invention provides a positive electrode plate, wherein the positive electrode plate comprises the carbon-coated lithium manganese oxide positive electrode material described in the second aspect.

[0024] In a fourth aspect, an embodiment of the present invention provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect above.

[0025] The preparation method of the positive electrode material provided in the embodiment of the present invention uses hydrogen peroxide to promote the carbonization of a low-melting-point organic carbon source at low temperature, which can shorten the carbonization time, obtain a pre-oxidized organic carbon source by oxidizing and dehydrating the organic carbon source, and then use the pre-oxidized organic carbon source to achieve low-temperature coating of lithium manganate, thereby obtaining a carbon-coated lithium manganate positive electrode material. The outer coating carbon layer improves the conductivity of the lithium manganate positive electrode material, and can play a binding role in the process of charging and discharging to inhibit the Mn 2+ The dissolution of Mn 2+ Migrate to the negative electrode, therefore, can significantly improve the rate performance and cycle stability of lithium manganese oxide positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for preparing a carbon-coated lithium manganate positive electrode material according to an embodiment of the present invention;

[0027] Figure 2 This is a scanning electron microscope (SEM) image of the carbon-coated lithium manganese oxide positive electrode material prepared in Example 1 of the present invention;

[0028] Figure 3 This is an X-ray diffraction (XRD) pattern of the carbon-coated lithium manganate positive electrode material prepared in Example 2 of the present invention;

[0029] Figure 4 The 100-cycle retention rate curve of Example 1 of the present invention and Comparative Example 1 is shown. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0031] The present invention provides a method for preparing a carbon-coated lithium manganese oxide positive electrode material, the main steps of which are as follows: Figure 1 As shown, including:

[0032] Step 110, mixing the lithium source and the manganese source to obtain a mixed material;

[0033] Specifically, the lithium source includes lithium hydroxide and / or lithium carbonate; the manganese source includes one of α-MnO2, β-MnO2, R-MnO2, Mn2O3 or Mn3O4; and the particle size of the manganese source is 3 to 14 μm.

[0034] The mixing process of the lithium source and the manganese source specifically includes:

[0035] Mix appropriate amounts of lithium source and manganese source according to the molar ratio using a high-speed mixer; or,

[0036] An excess lithium source and an appropriate amount of manganese source are mixed in a high-speed mixer according to a molar ratio; wherein the excess of the lithium source according to the molar ratio does not exceed 11%.

[0037] The mixing speed of the high-speed mixer is 400 to 2300 r / min, and the mixing time is 5 to 40 min.

[0038] Step 120, calcining the mixed material under air conditions to obtain a lithium manganate precursor;

[0039] Specifically, the heating rate of calcination is 3-6°C / min; the sintering temperature of calcination is 650-850°C; and the heat preservation time of calcination is 10-20h.

[0040] Step 130, mixing the organic carbon source and the hydrogen peroxide solution in a certain mass ratio under ultrasonic conditions to obtain a pre-oxidation treated organic carbon source mixed solution;

[0041] Organic carbon sources include maltitol and / or triethanolamine;

[0042] The mass ratio of the organic carbon source to the hydrogen peroxide solution is 1:1.5-1:2.

[0043] In this scheme, hydrogen peroxide is used to promote the carbonization of the low melting point organic carbon source at low temperature, which can shorten the carbonization time. In this scheme, the main function of hydrogen peroxide (H2O2) is to clean and oxidize the organic carbon source. In this embodiment, the concentration of hydrogen peroxide used is 5%-20%.

[0044] Additionally, organic carbon sources may contain impurities or unreacted organic matter that may affect the quality of the final product. Hydrogen peroxide is also used as an oxidizing and cleaning agent, helping to remove impurities and organic residues.

[0045] Step 140, adding the lithium manganate precursor to the pre-oxidized organic carbon source mixed solution, ultrasonically homogenizing to obtain a suspension, and low-temperature drying the suspension at 180° C.-250° C. to obtain a carbon-coated lithium manganate positive electrode material.

[0046] The mass ratio of the organic carbon source to the lithium manganate precursor is 1:9 to 4:6;

[0047] The ultrasonic mixing is carried out in an ultrasonic pulverizer, the ultrasonic power is 110 to 180 W, and the ultrasonic time is 0.5 to 2 h.

[0048] The preparation method of the carbon-coated lithium manganate positive electrode material provided in the embodiment of the present invention uses hydrogen peroxide to promote the carbonization of a low-melting-point organic carbon source at low temperature, which can shorten the carbonization time, and obtains a pre-oxidized organic carbon source by oxidizing and dehydrating the organic carbon source, and then uses the pre-oxidized organic carbon source to achieve low-temperature coating of lithium manganate, thereby obtaining a carbon-coated lithium manganate positive electrode material. The outer coating carbon layer improves the conductivity of the lithium manganate positive electrode material, and can play a binding role in the process of charging and discharging to inhibit the Mn 2+ The dissolution of Mn 2+ Migrate to the negative electrode, therefore, can significantly improve the rate performance and cycle stability of lithium manganese oxide positive electrode materials.

[0049] The spinel phase of the carbon-coated lithium manganate positive electrode material prepared by the present invention has a particle size of 8 to 14 μm, and the material can be applied to the positive electrode sheet of a lithium ion battery.

[0050] In order to more clearly illustrate the purpose and advantages of the present invention, the present invention is further described below in conjunction with the embodiments. In addition, the embodiments described in the present invention are only partial embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention. In addition, it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, that is, they are not intended to limit the protection scope of the present invention.

[0051] Example 1

[0052] Step (I), weighing manganese tetraoxide and lithium carbonate according to the stoichiometric ratio, mixing in a high-speed mixer to obtain a mixture, the speed of the high-speed mixer is 1500r / min, and the mixing time is 20min; wherein the particle size D50 of manganese tetraoxide is 6.2μm, and the particle size D50 of lithium carbonate is 5.8μm.

[0053] Step (II), the mixture in step (I) is heated to 750°C at a heating rate of 5°C / min in an air atmosphere, and the calcination holding time is 12h to obtain a lithium manganate positive electrode material precursor.

[0054] Step (III), weigh 20 g of triethanolamine and 30 g of hydrogen peroxide solution, pour them into a 250 mL beaker, use an ultrasonic cell crusher to sonicate for 0.5 h at an ultrasonic power of 120 W to obtain a uniform dispersion.

[0055] Step (IV), add 80g of the lithium manganate precursor in step (II) to the dispersion in step (III) and continue ultrasonication for 0.5h at the same ultrasonic power to obtain a uniform suspension. Pour the suspension into a crucible and place it in a blast drying oven, and dry it at 200°C to obtain a carbon-coated lithium manganate positive electrode material.

[0056] Example 2

[0057] Step (I), weighing manganese tetraoxide and 6% excess lithium carbonate according to a stoichiometric ratio and mixing them in a high-speed mixer to obtain a mixture, the speed of the high-speed mixer is 1500r / min, and the mixing time is 20min; wherein the particle size of manganese tetraoxide is 6.2μm, and the particle size of lithium carbonate is 5.8μm.

[0058] Step (II), heating the mixture in step (I) to a calcination temperature of 750°C at a heating rate of 5°C / min in an air atmosphere, and calcining for 12 hours to obtain a lithium manganate positive electrode material precursor.

[0059] Step (III), weigh 20 g of triethanolamine and 30 g of hydrogen peroxide solution, pour them into a 250 mL beaker, use an ultrasonic cell crusher to sonicate for 0.5 h at an ultrasonic power of 120 W to obtain a uniform dispersion.

[0060] Step (IV), add 30g of the lithium manganese oxide precursor in step (II) to the dispersion in step (III) and continue ultrasonication for 0.5h at the same ultrasonic power to obtain a uniform suspension. Pour the suspension into a crucible and place it in a blast drying oven, and dry it at 200°C to obtain a carbon-coated lithium manganese oxide positive electrode material.

[0061] Example 3

[0062] Step (I), weighing manganese tetraoxide and 10% excess lithium carbonate according to a stoichiometric ratio and mixing them in a high-speed mixer to obtain a mixture, the speed of the high-speed mixer is 1700r / min, and the mixing time is 15min; wherein the particle size of manganese tetraoxide is 8.8μm, and the particle size of lithium carbonate is 5.8μm.

[0063] Step (II), heating the mixture in step (I) to a calcination temperature of 720°C at a heating rate of 5°C / min under air atmosphere, and calcining for 20 hours to obtain a lithium manganate positive electrode material precursor.

[0064] Step (III), weigh 30 g of maltitol and 60 g of hydrogen peroxide solution into a 250 mL beaker, and use an ultrasonic cell crusher to sonicate for 1 h at an ultrasonic power of 160 W to obtain a uniform dispersion.

[0065] Step (IV), add 70g of the lithium manganate precursor in step (II) to the dispersion in step (III) and continue ultrasonication for 0.9h at the same ultrasonic power to obtain a uniform suspension. Pour the suspension into a crucible and place it in a blast drying oven, and dry it at 220°C to obtain a carbon-coated lithium manganate positive electrode material.

[0066] Example 4

[0067] Step (I), weighing β-MnO2 and an excess of 5% lithium hydroxide in a high-speed mixer according to a stoichiometric ratio to obtain a mixture, the speed of the high-speed mixer is 2000r / min, and the mixing time is 20min; wherein the particle size D50 of β-MnO2 is 5.2μm, and the particle size of lithium carbonate is 4.8μm.

[0068] Step (II), heating the mixture in step (I) to a calcination temperature of 850°C at a heating rate of 4°C / min in an air atmosphere, and calcining for 14 hours to obtain a lithium manganate positive electrode material precursor.

[0069] Step (III), weigh 20 g of maltitol and 30 g of hydrogen peroxide solution into a 250 mL beaker, and use an ultrasonic cell crusher to sonicate for 0.5 h at an ultrasonic power of 120 W to obtain a uniform dispersion.

[0070] Step (IV), add 30g of the lithium manganese oxide precursor in step (II) to the dispersion in step (III) and continue ultrasonication for 0.5h at the same ultrasonic power to obtain a uniform suspension. Pour the suspension into a crucible and place it in a blast drying oven, and dry it at 200°C to obtain a carbon-coated lithium manganese oxide positive electrode material.

[0071] Example 5

[0072] Step (I), weighing α-Mn02 and an excess of 8% lithium carbonate in a high-speed mixer according to a stoichiometric ratio and mixing them to obtain a mixture, the speed of the high-speed mixer is 1500r / min, and the mixing time is 30min; wherein the particle size D50 of α-Mn02 is 5.8μm, and the particle size of lithium carbonate is 4.6μm.

[0073] Step (II), heating the mixture in step (I) to a calcination temperature of 800°C at a heating rate of 5°C / min under air atmosphere, and calcining for 10 hours to obtain a lithium manganate positive electrode material precursor.

[0074] Step (III), weigh 20 g of maltitol and 40 g of hydrogen peroxide solution, pour them into a 250 mL beaker, use an ultrasonic cell crusher to sonicate for 1.5 h at an ultrasonic power of 150 W to obtain a uniform dispersion.

[0075] Step (IV), add 30g of the lithium manganese oxide precursor in step (II) to the dispersion in step (III) and continue ultrasonication for 0.5h at the same ultrasonic power to obtain a uniform suspension. Pour the suspension into a crucible and place it in a blast drying oven, and dry it at 200°C to obtain a carbon-coated lithium manganese oxide positive electrode material.

[0076] Comparative Example 1

[0077] Step (I), weighing manganese tetraoxide according to the stoichiometric ratio, and mixing it with 6% excess lithium carbonate in a high-speed mixer to obtain a mixture, the speed of the high-speed mixer is 1500r / min, and the mixing time is 20min; wherein the particle size of manganese tetraoxide is 6.2μm, and the particle size of lithium carbonate is 5.8μm.

[0078] Step (II), raising the temperature of the mixture in step (I) to 750°C at a heating rate of 5°C / min under air atmosphere, and calcining for 12 hours to obtain an uncoated lithium manganate positive electrode material.

[0079] Comparative Example 2

[0080] Step (I), weighing manganese tetraoxide and lithium carbonate according to the stoichiometric ratio and mixing them in a high-speed mixer to obtain a mixture, the speed of the high-speed mixer is 1500r / min, and the mixing time is 20min; wherein the particle size of manganese tetraoxide is 6.2μm, and the particle size of lithium carbonate is 5.8μm.

[0081] Step (II), heating the mixture in step (I) to a calcination temperature of 750°C at a heating rate of 5°C / min under air atmosphere, and calcining for 12 hours to obtain a lithium manganate positive electrode material precursor.

[0082] The carbon-coated lithium manganese oxide positive electrode material prepared in Example 1 was subjected to electron microscopy scanning, and the scanning electron microscopy image is as follows: Figure 2 As shown, it can be seen that the lithium manganese oxide material is composed of tightly stacked primary particles with relatively uniform size, clear edges and corners and a prism structure; in addition, it can be seen that the organic carbon source is distributed in the form of granular points on the surface of the lithium manganese oxide particles after carbonization, which restrains and hinders the dissolution and migration of manganese ions during the charge and discharge process, thereby enhancing the cycle stability of the material.

[0083] The carbon-coated lithium manganese oxide positive electrode material prepared in Example 2 was subjected to XRD testing. The XRD pattern is shown in FIG. Figure 3 As shown, it can be seen that the diffraction peak position and relative intensity of the carbon-coated lithium manganese oxide positive electrode material prepared in Example 2 are consistent with the standard cubic phase spinel structure, and no impurity peak appears, indicating that the carbon-coated positive electrode material obtained in Example 2 is a spinel phase, and the low melting and boiling point organic carbon source does not destroy the structure of the lithium manganese oxide itself during the low-temperature carbonization process.

[0084] The lithium manganate positive electrode material obtained from the above-mentioned embodiments and comparative examples was used as the positive electrode active material, and it was mixed with the conductive agent Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5 to obtain a positive electrode slurry. The positive electrode slurry was coated on the current collector aluminum foil using an automatic coating machine with a coating thickness of 110 μm, and the positive electrode sheet was obtained after drying. The positive electrode shell, positive electrode sheet, diaphragm, electrolyte, negative electrode, gasket, spring and negative electrode shell were stacked and assembled in sequence to obtain a battery. Among them, the diaphragm used a polypropylene (PP) base film, and the electrolyte used a conventional lithium ion electrolyte 1mol / L LiPF6 dissolved in a solvent with a volume ratio of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:1. After the battery was assembled, it was cycled 2 times at 0.1C in the voltage range of 3.0 to 4.3V, and then cycled 100 times at a rate of 1C. The 100-week cycle stability curves of the batteries of Example 1 and Comparative Example 1 are as follows: Figure 3 The test results of the 100-cycle capacity retention rate and the first-cycle discharge gram capacity of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0085]

[0086] Table 1

[0087] It can be seen from Table 1 above that:

[0088] According to Table 1 and Figure 4 The results of the 100-week cycle retention rate at a current density of 1C show that the carbon-coated lithium manganese oxide positive electrode material was obtained by low-temperature rapid evaporation method, using hydrogen peroxide to assist low melting and boiling point organic carbon sources to carbonize on the surface of the lithium manganese oxide precursor under low temperature conditions. Compared with the uncoated lithium manganese oxide, although the gram capacity of the carbon-coated lithium manganese oxide is reduced by about 3mAh / g, the first week efficiency and cycle retention rate are improved. This shows that the outer coating carbon layer improves the conductivity of the lithium manganese oxide positive electrode material, and can play a binding role in the process of charging and discharging to inhibit the Mn 2+ The dissolution of Mn 2+ Migrate to the negative electrode, therefore, can significantly improve the rate performance and cycle stability of lithium manganese oxide positive electrode materials.

[0089] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: The preparation method comprises: The lithium source and the manganese source are mixed to obtain a mixed material; calcining the mixed material under air conditions to obtain a lithium manganate precursor; The organic carbon source and the hydrogen peroxide solution are mixed uniformly under ultrasonic conditions in a certain mass ratio to obtain a pre-oxidized organic carbon source mixed solution; The lithium manganate precursor is added to the pre-oxidized organic carbon source mixed solution, ultrasonically homogenized to obtain a suspension, and the suspension is low-temperature dried at 180° C.-250° C. to obtain a carbon-coated lithium manganate positive electrode material.

2. The preparation method according to claim 1, characterized in that: The mixing of the lithium source and the manganese source specifically comprises: Mix appropriate amounts of lithium source and manganese source according to the molar ratio using a high-speed mixer; or, An excess lithium source and an appropriate amount of manganese source are mixed in a high-speed mixer according to a molar ratio; wherein the excess of the lithium source according to the molar ratio does not exceed 11%.

3. The preparation method according to claim 2, characterized in that: The mixing speed of the high-speed mixer is 400-2300 r / min, and the mixing time is 5-40 min.

4. The preparation method according to claim 1, characterized in that: The lithium source includes lithium hydroxide and / or lithium carbonate; The manganese source includes one of α-MnO2, β-MnO2, R-MnO2, Mn2O3 or Mn3O4; the particle size of the manganese source is 3 to 14 μm.

5. The preparation method according to claim 1, characterized in that: The organic carbon source includes maltitol and / or triethanolamine; The mass ratio of the organic carbon source to the hydrogen peroxide solution is 1:1.5-1:2; The concentration of the hydrogen peroxide is 5%-20%.

6. The preparation method according to claim 1, characterized in that: The heating rate of the calcination is 3-6°C / min; the sintering temperature of the calcination is 650-850°C; and the heat preservation time of the calcination is 10-20h.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the organic carbon source to the lithium manganate precursor is 1:9 to 4:6; The ultrasonic mixing is carried out in an ultrasonic pulverizer, the ultrasonic power is 110-180W, and the ultrasonic time is 0.5-2h.

8. A carbon-coated lithium manganese oxide positive electrode material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The lithium manganese oxide positive electrode material is a spinel phase, and the particle size of the carbon-coated lithium manganese oxide positive electrode material is 8 to 14 μm.

9. A positive electrode sheet, characterized in that: The positive electrode plate comprises the carbon-coated lithium manganese oxide positive electrode material as described in claim 9 above.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet as described in claim 9 above.

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