Preparation method of ternary positive electrode material, lithium battery and electric vehicle

Abstract

The application discloses a preparation method of a ternary positive electrode material, a lithium battery and an electric vehicle, and aims to improve the cycle performance of the ternary positive electrode material prepared from a polycrystal precursor. The method comprises the following steps: uniformly mixing a polycrystal ternary precursor and coarse lithium hydroxide to obtain a first mixture; performing pre-sintering treatment on the first mixture; uniformly mixing the product of the pre-sintering treatment and an additive to obtain a second mixture; and performing high-temperature sintering treatment on the second mixture to obtain a ternary positive electrode material.

Description

Technical Field

[0001] The present application relates to the field of lithium battery technology, and in particular to a method for preparing a ternary positive electrode material, a lithium battery, and an electric vehicle. Background Art

[0002] With the development of new energy technologies, lithium batteries have been widely used in various fields. Common approaches to reducing lithium battery production costs include improving process steps or replacing low-cost materials. Coarse powdered lithium hydroxide offers the advantage of low cost due to its simple preparation process. However, cathode materials prepared by mixing coarse powdered lithium hydroxide with polycrystalline ternary precursors suffer from poor cycling performance. Summary of the Invention

[0003] The present application provides a method for preparing a ternary positive electrode material, a lithium battery and an electric vehicle, which are used to improve the cycle performance of the ternary positive electrode material prepared from a polycrystalline precursor.

[0004] In a first aspect, the present application provides a method for preparing a ternary cathode material, comprising:

[0005] uniformly mixing the polycrystalline ternary precursor and the coarse powdered lithium hydroxide to obtain a first mixture;

[0006] performing a pre-sintering process on the first mixture;

[0007] uniformly mixing the pre-sintered product with an additive to obtain a second mixture;

[0008] The second mixture is subjected to high-temperature sintering treatment to obtain a ternary positive electrode material.

[0009] The embodiment of the present application adds additives after pre-sintering, mixes the additives with the pre-sintering products, and realizes the doping of the additives into the positive electrode material during the high-temperature sintering process. This avoids the problem of excessive mechanical force used for mixing causing the polycrystalline ternary precursor to crack when the additives are directly mixed into the polycrystalline ternary precursor and coarse powder lithium hydroxide, thereby effectively improving the cycle performance of the ternary positive electrode material.

[0010] In one possible implementation manner, the median diameter of the coarse powder of lithium hydroxide is 50-500 microns.

[0011] In a possible embodiment, the precursor is selected from: x Co y Mn z Al 1-x-y-z (OH)2 hydroxide precursor, molecular formula is Ni x Co y Mn z Al 1-x-y-zO oxide precursor, the molecular formula is Ni x Co y Mn z Al 1-x-y-z A carbonate precursor of CO3; each x, y, and z independently satisfy the following: 0.3<x<1, 0≤y<0.3, 0≤z<0.75, 0≤1-xyz≤0.2.

[0012] In a possible embodiment, the molecular formula of the ternary cathode material is: Li k Ni a Co b Mn c Al e M 1-a-b-c-e O2; among them,

[0013] M corresponds to the metal ion in the additive, 0<1-abce≤0.03, k>0, 0.3<a<1, 0≤b<0.3, 0≤c<0.75, 0≤e≤0.2; and when one of c and e is 0, the other is not 0.

[0014] In one possible implementation, the additive is at least one of aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, zirconium oxide, zirconium hydroxide, cobalt oxide, cobalt hydroxide, zinc oxide, and zinc hydroxide.

[0015] In a possible implementation manner, the pre-sintering temperature of the pre-sintering treatment is 450-700° C., and the pre-sintering time is 2-16 hours.

[0016] In a possible implementation manner, the first mixture is obtained under the condition that the mixing frequency is not greater than 25 Hz; and the second mixture is obtained under the condition that the mixing frequency is not less than 30 Hz.

[0017] In a possible implementation manner, the pre-sintering treatment and the high-temperature sintering treatment are performed in a roller kiln, a rotary kiln or a pusher kiln.

[0018] In one possible implementation, the second mixture is subjected to a high-temperature sintering process to obtain a ternary positive electrode material, comprising:

[0019] The second mixture is subjected to high-temperature sintering treatment to obtain a third mixture; wherein the third mixture includes impurities generated during the operation of the rotary kiln, roller kiln, or pusher kiln;

[0020] The third mixture is sieved and demagnetized to obtain a ternary positive electrode material.

[0021] In one possible embodiment, the high-temperature sintering treatment includes a first sintering treatment and a second sintering treatment; wherein, the first sintering temperature of the first sintering treatment is 600-900°C, and the first sintering time is 12-24 hours; the second sintering temperature of the second sintering treatment is 400-700°C, and the second sintering time is 8-20 hours.

[0022] In a second aspect, the present application provides a lithium battery, comprising:

[0023] The ternary positive electrode material is prepared by the method described in the first aspect and any possible embodiment.

[0024] In a third aspect, the present application provides an electric vehicle, comprising:

[0025] The lithium battery as described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic flow chart of a method for preparing a ternary cathode material provided in an embodiment of the present application;

[0027] Figure 2 This is a comparison chart of the cycle performance of device example 21 and device comparison example 21 in the embodiments of this application. DETAILED DESCRIPTION

[0028] In response to the problem of poor cycle performance of ternary positive electrode materials made from polycrystalline ternary precursors in the prior art, the present application proposes a method for preparing ternary positive electrode materials: by adding additives after pre-sintering treatment, the additives are mixed evenly with the pre-sintered product, and then high-temperature sintering treatment is performed to avoid mixing additives before pre-sintering. The additives have high requirements on the strength of the mechanical force used for mixing, which causes the coarse powder lithium hydroxide to destroy the polycrystalline ternary precursor under high-intensity mechanical force, thereby affecting the cycle performance of the positive electrode material.

[0029] The following will be combined with the accompanying drawings to describe in detail the specific implementation methods of a method for preparing a ternary positive electrode material, a lithium battery, and an electric vehicle provided in the embodiments of the present application. It should be noted that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the embodiments of the present application.

[0030] Please refer to Figure 1 The present application proposes a method for preparing a ternary cathode material to improve the cycle performance of the ternary cathode material prepared from a polycrystalline ternary precursor. The method specifically includes the following implementation steps:

[0031] Step 101: uniformly mix a polycrystalline ternary precursor and coarse powder lithium hydroxide to obtain a first mixture.

[0032] In the embodiment of the present application, the median diameter D of the coarse powder lithium hydroxide 50 Between 50-500 microns.

[0033] The molar ratio between the polycrystalline ternary precursor and the coarse powder lithium hydroxide can be 1:1.01-1:1.06.

[0034] To ensure uniform mixing of the polycrystalline ternary precursor and the coarse powdered lithium hydroxide, the polycrystalline ternary precursor and the coarse powdered lithium hydroxide can be mixed in a plowshare mixer; the first mixture is obtained at a mixing frequency of no more than 25 Hz. Specifically, the mixing frequency can be between 3 and 25 Hz, and the mixing time can be between 3 and 50 minutes.

[0035] The polycrystalline ternary precursor described in the embodiment of the present application is selected from: Ni x Co y Mn z Al 1-x-y-z (OH)2 hydroxide precursor, molecular formula is Ni x Co y Mn z Al 1-x-y-z O oxide precursor, the molecular formula is Ni x Co y Mn z Al 1-x-y-z A carbonate precursor of CO3; each x, y, and z independently satisfy the following: 0.3<x<1, 0≤y<0.3, 0≤z<0.75, 0≤1-xyz≤0.2.

[0036] It should be noted that coarse powdered lithium hydroxide has the characteristics of large particles and high strength, while the polycrystalline ternary precursor has the characteristics of low strength. Therefore, when mixing the polycrystalline ternary precursor including the polycrystalline ternary precursor with the coarse powdered lithium hydroxide, if the mechanical force used for mixing is too great, the coarse powdered lithium hydroxide will easily crush the polycrystalline ternary precursor, causing the secondary spheres of the polycrystalline ternary precursor to break. In particular, when mixing by vibration, the coarse powdered lithium hydroxide can obtain high kinetic energy during the high-frequency vibration process, causing the polycrystalline ternary precursor to break into spheres and change the morphology of the polycrystalline ternary precursor, thereby reducing the performance of the polycrystalline ternary precursor.

[0037] Step 102: pre-sintering the first mixture.

[0038] Specifically, the pre-sintering process can be carried out in a roller kiln, a rotary kiln or a pusher kiln.

[0039] The pre-sintering temperature of the pre-sintering treatment is 450-700° C., the pre-sintering time is 2-16 hours, and the pre-sintering heating rate can be set to any value less than or equal to 15° C. / min.

[0040] Step 103: uniformly mixing the pre-sintered product with additives to obtain a second mixture.

[0041] The second mixture can still be mixed in a plowshare mixer or a high-speed mixer. Since the metal ions in the additives are present in the ternary cathode material in the form of doping, the amount of additives added is significantly less than that of the pre-sintered product.

[0042] The additive may be at least one of aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, zirconium oxide, zirconium hydroxide, cobalt oxide, cobalt hydroxide, zinc oxide, and zinc hydroxide.

[0043] Furthermore, in order to ensure that the additives are uniformly mixed with the pre-sintered product, the second mixture is obtained at a mixing frequency of not less than 30 Hz, specifically, the mixing frequency may be 30-50 Hz, and the mixing time may be 50 minutes.

[0044] Step 104: performing high-temperature sintering on the second mixture to obtain a ternary positive electrode material.

[0045] The high-temperature sintering treatment in the embodiment of the present application can be carried out in a roller kiln, a rotary kiln or a pusher kiln so that the second mixture can always be in a dynamic sintering process. However, during the high-temperature sintering process in the above-mentioned kilns (roller kiln, rotary kiln or pusher kiln), it is easy for impurities such as slag to be mixed into the high-temperature sintered product. Therefore, in one embodiment of the present application, the third mixture obtained by the high-temperature sintering treatment of the second mixture is also screened to remove large particles of impurities; and demagnetized to remove magnetic impurities (for example, iron slag) in the third mixture, and finally obtain a ternary positive electrode material.

[0046] In the ternary cathode material, the metal ions correspond to the metal ions in the polycrystalline ternary precursor. The molecular formula of the ternary cathode material is Li k Ni a Co b Mn c Al e M 1-a-b-c-e O2; among them,

[0047] M corresponds to the metal ion in the additive, 0<1-abce≤0.3, k>0, 0.3<a<1, 0≤b<0.3, 0≤c<0.75, 0≤e≤0.2; and when one of c and e is 0, the other is not 0.

[0048] Furthermore, the high-temperature sintering process can be a single-stage or multi-stage sintering process. Furthermore, when the high-temperature sintering process is a multi-stage sintering process, a coating agent can be introduced between the multiple sintering processes. The high-temperature sintering process before the introduction of the coating agent can be referred to as the first sintering process, and the high-temperature sintering process after the introduction of the coating agent can be referred to as the second sintering process. Since the purpose of the second sintering process is to add a coating layer to the positive electrode material, the second sintering temperature is lower than the first sintering temperature.

[0049] Specific high-temperature sintering parameters can be: the first sintering temperature of the first sintering treatment is 600-900°C, the first heating rate can be 2-10°C / min, and the first sintering time is 12-24 hours; the second sintering temperature of the second sintering treatment is 250-600°C, the second heating rate can be 5-20°C / min, and the second sintering time is 8-20 hours.

[0050] The coating agent may be at least one of Al(OH)3, B(OH)3, H3BO3, TiO2, and Ti(OH)4.

[0051] Correspondingly, the molecules of the ternary cathode material with the coating layer can be: Li k Ni a Co b Mn c Al e M 1-a-b-c-e O2@R f O g ; Wherein, M corresponds to the metal ion in the additive, 0<1-abce≤0.3, k>0, 0.3<a<1, 0≤b<0.3, 0≤c<0.75, 0≤e≤0.2; and when one of c and e is 0, the other is not 0; R corresponds to the metal ion in the coating agent, and f and g are determined according to the valence state of different metal elements.

[0052] The following is further explained through Synthesis Examples 1-2, Synthesis Comparative Example 1, Device Examples 11-12, 21-22, and Device Comparative Examples 11 and 21.

[0053] Synthesis Example 1

[0054] S1, make polycrystalline ternary precursor Ni 0.82 Co 0.12 Mn 0.06 (OH)2 (median diameter of 11 microns) and coarse powdered lithium hydroxide were mixed at a molar ratio of 1:1.04 in a high-speed mixer at a mixing frequency of 25 Hz for 30 minutes to obtain a first mixture.

[0055] S2. Place the first mixture in a roller kiln for pre-sintering treatment: the pre-sintering temperature is 550° C., and the pre-sintering time is 7 hours.

[0056] S3. Mix the pre-sintered product and the additive (zirconium oxide) in a high-speed mixer at a frequency of 35 Hz for 50 minutes to obtain a second mixture.

[0057] S4. Place the second mixture in a roller kiln for a first high-temperature sintering: the first sintering temperature is 780°C, the heating rate is 5-10°C / min, and the first sintering time is 18 hours; obtain a first intermediate product; after screening and demagnetization, add the coating agent H3BO3 and perform a second high-temperature sintering: the second sintering temperature is 320°C, the second heating rate is 15°C / min, and the second sintering time is 16 hours; screen and demagnetize the obtained product to obtain a ternary positive electrode material.

[0058] Synthesis Example 2

[0059] S1, make polycrystalline ternary precursor Ni 0.82 Co 0.12 Mn 0.06 (OH)2 (median diameter of 11 microns) and coarse powdered lithium hydroxide were mixed at a molar ratio of 1:1.04 in a high-speed mixer at a mixing frequency of 25 Hz for 30 minutes to obtain a first mixture.

[0060] S2. Place the first mixture in a roller kiln for pre-sintering treatment: the pre-sintering temperature is 600° C., and the pre-sintering time is 7 hours.

[0061] S3. Mix the pre-sintered product and the additive (zirconium oxide) in a high-speed mixer at a frequency of 35 Hz for 50 minutes to obtain a second mixture.

[0062] S4. The second mixture is placed in a roller kiln for a first high-temperature sintering process at a temperature of 780°C for 18 hours to obtain a first intermediate product. After screening and demagnetization, a coating agent, H3BO3, is added and a second high-temperature sintering process is performed at a temperature of 320°C for 16 hours. The obtained product is screened and demagnetized to obtain a ternary positive electrode material.

[0063] Comparative Synthesis Example 1

[0064] S1, make polycrystalline ternary precursor Ni 0.82 Co 0.12 Mn 0.06 (OH)2 (median diameter of 11 microns), coarse powder lithium hydroxide, and additive (zirconium oxide) were mixed in a high-speed mixer at a mixing frequency of 35 Hz at a molar ratio of 1:1.04 for 50 minutes to obtain a first mixture.

[0065] S2. Place the first mixture in a roller kiln for pre-sintering treatment: the pre-sintering temperature is 600° C., and the pre-sintering time is 7 hours.

[0066] S3. Place the first mixture in a roller kiln for a first high-temperature sintering: the first sintering temperature is 780°C, the heating rate is 5-10°C / min, and the first sintering time is 18 hours; obtain a first intermediate product; after screening and demagnetization, add the coating agent H3BO3 and perform a second high-temperature sintering: the second sintering temperature is 320°C, the second heating rate is 15°C / min, and the second sintering time is 16 hours; screen and demagnetize the obtained product to obtain a ternary positive electrode material.

[0067] Device Examples 11-12, 21-22, Device Comparative Examples 11, 21

[0068] Device Examples 11-12 and Comparative Example 11 are button-type lithium-ion batteries prepared using Synthesis Examples 1-2 and Comparative Example 1 as positive electrode materials. Device Examples 21-22 and Comparative Example 21 are full batteries prepared using Synthesis Examples 1-2 and Comparative Example 1 as positive electrode materials.

[0069] The preparation of device examples 11-12 and device comparative example 11 is described below:

[0070] Step S1: Dissolve the positive electrode material, acetylene black (conductive agent), and polyvinyl diene (PVDF binder) in 2-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2 to prepare a viscous slurry. Apply the slurry evenly to the surface of aluminum foil and then dry. Drying can be done in an oven at 135°C (do not use a vacuum oven) for 0.5 hours.

[0071] Step S2: Use a punching machine to cut the dried aluminum foil into circular electrode sheets (up to 11 mm in diameter). The surface current collector loading on each electrode sheet is 15 mg / cm2. The sheets are then placed in a vacuum oven (120°C) and dried for 2 hours to remove trace moisture. Finally, they are stored in a glove box under an argon atmosphere.

[0072] Step S3: Use the electrode sheet stored in the glove box as the positive electrode sheet and the lithium sheet as the negative electrode. Separate the positive and negative electrodes with a separator and add 30 μL of a commercial ternary electrolyte (LiPF6 / EC-DEC-EMC, 1:1:1 volume ratio). Assemble the positive electrode shell, positive electrode sheet, separator, lithium sheet, gasket, and spring in this order. Finally, seal the package using a sealing machine to obtain a lithium-ion button cell.

[0073] The preparation of device examples 21-22 and device comparative example 21 is described below:

[0074] The positive electrode active material, conductive carbon Super P, KS6 and polyvinylidene fluoride (HSV900) were mixed and homogenized in a mass ratio of 94.5%:2%:1%:2.5%, then evenly coated on aluminum foil and dried. The surface density was controlled at 16 mg / cm2 per side. A double-roller machine was used to roll the positive electrode sheet with a compaction density of 3.0 g / cm3, and then the positive electrode sheet was placed in a vacuum drying oven and dried at 120°C for 10 hours. The positive electrode sheet, separator, and negative electrode sheet were wound into a battery cell with a designed nominal capacity of 600 mAh, an NP ratio of 1.12, a liquid injection of 3 g, a PP / PE composite separator, a graphite negative electrode, and a high-voltage electrolyte (Xinzhoubang LBC502A50) to obtain a full lithium-ion battery.

[0075] The initial discharge capacity and initial coulombic efficiency of lithium-ion button cells were measured at 0.2C over a voltage range of 2.5-4.25V. The capacity retention of the full lithium-ion battery was measured after 100 cycles at 1C. Please refer to Table 1.

[0076] Table 1

[0077]

[0078] As can be seen from Table 1, the performance of device examples 11-12, 21-22 is better than that of device comparison examples 11 and 21. Figure 2 It can be seen that the cycle retention rate of device embodiment 21 is better than that of device comparison example 21.

[0079] It can be seen that in device embodiments 11-12, and 21-22, by controlling the steps of adding additives, damage to the secondary spheres of the polycrystalline precursor during mixing of the additives is avoided, thereby effectively improving the cycle performance, first coulombic efficiency, and discharge specific capacity of the ternary positive electrode material and the corresponding lithium battery.

[0080] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a ternary cathode material, characterized in that: include: The polycrystalline ternary precursor and the coarse powder of lithium hydroxide are uniformly mixed to obtain a first mixture; the first mixture is obtained under the condition that the mixing frequency is not greater than 25 Hz; performing a pre-sintering process on the first mixture; uniformly mixing the pre-sintered product with an additive to obtain a second mixture; performing a high-temperature sintering treatment on the second mixture to obtain a ternary positive electrode material; The metal ions in the additive are present in the ternary cathode material in a doped form; the pre-sintering temperature of the pre-sintering treatment is 450-700° C., and the high-temperature sintering treatment includes a first sintering treatment and a second sintering treatment.

2. The method according to claim 1, wherein The precursor is selected from: x Co y Mn z Al 1-x-y-z (OH)2 hydroxide precursor, molecular formula is Ni x Co y Mn z Al 1-x-y-z O oxide precursor, the molecular formula is Ni x Co y Mn z Al 1-x-y-z A carbonate precursor of CO3; each x, y, and z independently satisfy the following: 0.3<x<1, 0≤y<0.3, 0≤z<0.75, 0≤1-xyz≤0.

2.

3. The method according to claim 1, wherein The molecular formula of the ternary cathode material is: Li k Ni a Co b Mn c Al e M 1-a-b-c-e O2; in, M corresponds to the metal ion in the additive, 0<1-abce≤0.3, k>0, 0.3<a<1, 0≤b<0.3, 0≤c<0.75, 0≤e≤0.2; and when one of c and e is 0, the other is not 0.

4. The method according to claim 1, wherein The additive is at least one of aluminum oxide, aluminum hydroxide, magnesium oxide, magnesium hydroxide, zirconium oxide, zirconium hydroxide, cobalt oxide, cobalt hydroxide, zinc oxide and zinc hydroxide.

5. The method according to claim 1, wherein The pre-sintering time of the pre-sintering process is 2-16 hours.

6. The method according to any one of claims 1 to 5, wherein: The second mixture is obtained under the condition that the mixing frequency is not less than 30 Hz.

7. The method according to claim 1, wherein The pre-sintering process and the high-temperature sintering process are carried out in a roller kiln, a rotary kiln or a pusher kiln.

8. The method according to claim 1, wherein The first sintering temperature of the first sintering treatment is 600-900° C., and the first sintering time is 12-24 hours; the second sintering temperature of the second sintering treatment is 400-700° C., and the second sintering time is 8-20 hours.

9. A lithium battery, characterized in that: include: A ternary positive electrode material prepared by the method according to any one of claims 1 to 8.

10. An electric vehicle, characterized in that: include: The lithium battery according to claim 9.

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