Coating and mixing method for improving normal-temperature capacity and impedance of positive electrode material

Abstract

The invention discloses a coating mixing method for improving normal-temperature capacity and impedance of a positive electrode material, which comprises the following steps: weighing lithium cobalt oxide particles and a coating additive according to a certain proportion, putting the lithium cobalt oxide particles and the coating additive into a mixer, and mixing at a low-speed stage, a medium-speed stage and a high-speed stage to obtain a final mixture; wherein the coating additives are respectively fed in stages at a low-speed stage, a medium-speed stage and a high-speed stage. According to the coating and mixing method, additive coating on the surface of the material can be fluffy, full contact of a coating substance and the atmosphere in the roasting process is facilitated, and the normal-temperature capacity and impedance of the roasted positive electrode material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for lithium - ion batteries, and particularly relates to a coating and mixing method for improving the room - temperature capacity and impedance of cathode materials. Background Art

[0002] Currently, the modification of cathode materials mainly focuses on bulk doping and surface coating. Among them, surface coating modification is to mix lithium cobaltate particles and coating additives evenly and then calcine them to form a coating layer on the material surface to improve the room - temperature capacity, high - temperature cycle, and high - temperature storage performance of the material.

[0003] In the existing coating and mixing process, it is usually necessary to weigh lithium cobaltate particles and the designed amount of additives. After a pre - mixing stage with low rotation speed and short time and a mixing stage with high rotation speed and long time, this mixing method makes the cobalt oxide or hydroxide powder tightly wrap on the surface of lithium cobaltate particles, which is not conducive to the contact between the coating substance and the atmosphere during the sintering process, nor is it conducive to the uniform distribution of other additives in the coating layer, resulting in an increase in residual cobalt after calcination, an increase in the DCIR impedance of the material, and a decrease in capacity. Summary of the Invention

[0004] To solve the above - mentioned technical problems, the purpose of the present invention is to provide a coating and mixing method for improving the room - temperature capacity and impedance of cathode materials. This method combines low - speed mixing, medium - speed mixing, and high - speed mixing, and optimizes the mixing time. The cobalt oxide or hydroxide and other additives are added in stages during the mixing process, making the additives wrapped on the material surface more fluffy and the distribution of additives in the coating layer more uniform, which is conducive to the full contact between the coating substance and the atmosphere during the calcination process, and improves the room - temperature capacity and impedance of the cathode material after calcination.

[0005] To achieve the above - mentioned technical purpose and technical effect, the present invention is realized through the following technical solutions:

[0006] The present invention provides a coating and mixing method for improving the room - temperature capacity and impedance of cathode materials, specifically as follows:

[0007] Weigh lithium cobaltate particles and coating additives according to a certain ratio, put the lithium cobaltate particles and coating additives into a mixer, and mix them through a low - speed stage, a medium - speed stage, and a high - speed stage to obtain the final mixture; among them, the coating additives are added in stages during the low - speed stage, the medium - speed stage, and the high - speed stage.

[0008] Furthermore, the coating additives are divided into three parts, namely additive one, additive two, and additive three; specifically, the mixing process includes the following steps:

[0009] (1) Put the lithium cobaltate particles and additive one into a mixer, and stir and mix at a rotation speed of 150 - 500 r / min for 3 - 7 min to obtain mixture one;

[0010] (2) Put additive two into the mixer and stir and mix it with the first mixture at a rotation speed of 900 - 1100 revolutions per minute for 20 - 35 minutes to obtain the second mixture.

[0011] (3) Put additive three into the mixer and stir and mix it with the second mixture at a rotation speed of 1300 - 1600 revolutions per minute for 10 - 15 minutes.

[0012] Further, the lithium cobalt oxide particles include large particles with a D50 of 17 - 20 μm and small particles with a D50 of 4 - 7 μm.

[0013] Further, in the lithium cobalt oxide particles, the mass ratio of the large particles to the small particles is (3 - 5):1.

[0014] Further, in step (1), the mass ratio of the lithium cobalt oxide particles to the coating additive is (15 - 30):1.

[0015] Further, the mass ratio of additive one, additive two, and additive three is (3.0 - 3.5):(5.0 - 5.5):(2 - 3).

[0016] Further, the coating additive includes cobalt oxides or hydroxides.

[0017] Further, in additive one, additive two, or additive three, there is also other element additive in addition to cobalt oxides or hydroxides, and this other element additive is selected from oxides or salts of at least one element among Al, Mg, Ti, Y, La, Ni, Mn, Zr, W, and Mo.

[0018] Further, when there are two or more additives in additive one, additive two, or additive three, these two or more additives are mixed by ball milling, the ball milling speed is 200 - 500 revolutions per minute, and the ball milling time is 20 - 150 minutes.

[0019] Further, additive one is cobalt oxide or hydroxide, additive two is a mixture of cobalt oxide or hydroxide and other element additive, and additive three is cobalt oxide or hydroxide.

[0020] Further, the proportion of the other element additive in the total amount of the coating additive is 2% - 3%.

[0021] The beneficial effects of the present invention are:

[0022] In the low-speed mixing stage of the present invention, the lithium cobaltate particles and additives can be preliminarily dispersed. In the medium-speed mixing stage, the contact between the lithium cobaltate particles and additives is further optimized. In the high-speed mixing stage, the additives are ensured to be evenly distributed. By optimizing the mixing time, local agglomeration caused by too fast mixing can be avoided.

[0023] The present invention adopts a staged mixing method for the additives, which can construct a coating layer layer by layer, ensuring a more uniform distribution of the additives on the particle surface, forming a more fluffy coating layer on the particle surface, and significantly increasing the porosity of the coating layer; this fluffy structure helps to provide a larger surface area during the roasting process, enabling the coating material to fully contact the atmosphere, promoting the uniform progress of chemical reactions, and reducing incomplete local reactions caused by a dense coating layer.

[0024] Generally speaking, in the present invention, a medium-speed mixing stage is introduced during the mixing process. Through the cooperation of low-speed mixing, medium-speed mixing, and high-speed mixing, and by optimizing the mixing time, especially the mixing time in the high-speed mixing stage, and adding cobalt oxides or hydroxides and other additives in stages, the additives on the material surface are wrapped more fluffily, and the distribution of the additives in the coating layer is more uniform, which is beneficial to the full contact between the coating material and the atmosphere during the roasting process, thereby improving the room-temperature capacity performance and impedance of the roasted cathode material. Description of the Drawings

[0025] Figure 1 SEM images of the mixed materials for Example 1, Comparative Example 1, and Comparative Example 2;

[0026] Figure 2 Charge-discharge curves of the roasted samples for Example 1, Comparative Example 1, and Comparative Example 2;

[0027] Figure 3 EIS test result graphs of the roasted samples for Example 1, Comparative Example 1, and Comparative Example 2. Detailed Embodiments

[0028] The technical solutions in the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0029] The present invention provides a coating mixing method for improving the room-temperature capacity and impedance of cathode materials, including the following steps:

[0030] (1) Weigh lithium cobaltate particles and coating additives in a certain proportion, and divide the coating additives into three parts according to a certain mass ratio, namely Additive 1, Additive 2, and Additive 3;

[0031] Among them, the lithium cobalt oxide particles include large particles with a D50 of 17 - 20 μm and small particles with a D50 of 4 - 7 μm; the mass ratio of the large particles to the small particles is (3 - 5):1; the mass ratio of the lithium cobalt oxide particles to the coating additive is (15 - 30):1; the mass ratio of additive one, additive two, and additive three is (3.0 - 3.5):(5.0 - 5.5):(2 - 3);

[0032] The coating additive includes cobalt oxides or hydroxides; additive one, additive two, or additive three also includes other elemental additives in addition to cobalt oxides or hydroxides, and the other elemental additives are selected from oxides or salts of at least one element among Al, Mg, Ti, Y, La, Ni, Mn, Zr, W, and Mo;

[0033] When there are two or more additives in additive one, additive two, or additive three, the two or more additives are mixed by ball milling, the ball milling speed is 200 - 500 revolutions per minute, and the ball milling time is 20 - 150 minutes;

[0034] Preferably, additive one is cobalt oxide or hydroxide, additive two is a mixture of cobalt oxide or hydroxide and other elemental additives, and additive three is cobalt oxide or hydroxide;

[0035] The proportion of the other elemental additives in the total amount of the coating additive is 2% - 3%;

[0036] (2) Put the lithium cobalt oxide particles and additive one into a mixer and stir - mix at a speed of 150 - 500 revolutions per minute for 3 - 7 minutes to obtain mixture one;

[0037] (3) Put additive two into the mixer and stir - mix with the mixture one at a speed of 900 - 1100 revolutions per minute for 20 - 35 minutes to obtain mixture two;

[0038] (4) Put additive three into the mixer and stir - mix with mixture two at a speed of 1300 - 1600 revolutions per minute for 10 - 15 minutes.

[0039] Example 1

[0040] A coating mixing method for improving the normal - temperature capacity and impedance of a cathode material, comprising the following steps:

[0041] (1) Weigh 8 kg of large cobalt lithium oxide particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 500 g of cobalt hydroxide and 15 g of alumina; divide the above cobalt hydroxide into powder 1 with a mass of 150 g, powder 2 with a mass of 250 g, and powder 3 with a mass of 100 g; ball-mill and mix powder 2 with 15 g of alumina at a ball-mill speed of 200 revolutions per minute for 80 minutes to obtain powder 4; use powder 1 as additive one, powder 4 as additive two, and powder 3 as additive three;

[0042] (2) Put the weighed cobalt lithium oxide particles and additive one into a mixer and stir and mix at a speed of 400 revolutions per minute for 3 minutes to obtain mixture one;

[0043] (3) Put additive two into the mixer and stir and mix with the mixture one at a speed of 1000 revolutions per minute for 20 minutes to obtain mixture two;

[0044] (4) Put additive three into the mixer and stir and mix with mixture two at a speed of 1600 revolutions per minute for 10 minutes to obtain the final mixture.

[0045] Example 2

[0046] A coating mixing method for improving the normal temperature capacity and impedance of a positive electrode material, comprising the following steps:

[0047] (1) Weigh 8 kg of large cobalt lithium oxide particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 500 g of cobalt hydroxide and 15 g of alumina; divide the above cobalt hydroxide into powder 1 with a mass of 150 g, powder 2 with a mass of 250 g, and powder 3 with a mass of 100 g; ball-mill and mix powder 2 with 15 g of alumina at a ball-mill speed of 200 revolutions per minute for 80 minutes to obtain powder 4; use powder 1 as additive one, powder 4 as additive two, and powder 3 as additive three;

[0048] (2) Put the weighed cobalt lithium oxide particles and additive one into a mixer and stir and mix at a speed of 200 revolutions per minute for 5 minutes to obtain mixture one;

[0049] (3) Put additive two into the mixer and stir and mix with the mixture one at a speed of 1000 revolutions per minute for 20 minutes to obtain mixture two;

[0050] (4) Put additive three into the mixer and stir and mix with mixture two at a speed of 1300 revolutions per minute for 12 minutes to obtain the final mixture.

[0051] Example 3

[0052] A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material, comprising the following steps:

[0053] (1) Weigh 8 kg of large lithium cobaltate particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 500 g of cobalt hydroxide and 15 g of alumina; divide the above cobalt hydroxide into powder 1 with a mass of 150 g, powder 2 with a mass of 250 g, and powder 3 with a mass of 100 g; ball-mill and mix powder 2 with 15 g of alumina at a ball-mill speed of 200 revolutions per minute for 80 minutes to obtain powder 4; use powder 1 as additive 1, powder 4 as additive 2, and powder 3 as additive 3;

[0054] (2) Put the weighed lithium cobaltate particles and additive 1 into a mixer and stir and mix at a speed of 300 revolutions per minute for 3 minutes to obtain mixture 1;

[0055] (3) Put additive 2 into the mixer and stir and mix with the mixture 1 at a speed of 1000 revolutions per minute for 20 minutes to obtain mixture 2;

[0056] (4) Put additive 3 into the mixer and stir and mix with mixture 2 at a speed of 1500 revolutions per minute for 10 minutes to obtain the final mixture.

[0057] Example 4

[0058] A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material, comprising the following steps:

[0059] (1) Weigh 8 kg of large lithium cobaltate particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 500 g of cobalt hydroxide and 15 g of alumina; divide the above cobalt hydroxide into powder 1 with a mass of 150 g, powder 2 with a mass of 250 g, and powder 3 with a mass of 100 g; ball-mill and mix powder 2 with 15 g of alumina at a ball-mill speed of 200 revolutions per minute for 80 minutes to obtain powder 4; use powder 1 as additive 1, powder 4 as additive 2, and powder 3 as additive 3;

[0060] (2) Put the weighed lithium cobaltate particles and additive 1 into a mixer and stir and mix at a speed of 500 revolutions per minute for 3 minutes to obtain mixture 1;

[0061] (3) Put additive two into the mixer and stir and mix it with the first mixture at a rotation speed of 1100 revolutions per minute for 20 minutes to obtain the second mixture;

[0062] (4) Put additive three into the mixer and stir and mix it with the second mixture at a rotation speed of 1300 revolutions per minute for 14 minutes to obtain the final mixture.

[0063] Example 5

[0064] A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material, comprising the following steps:

[0065] (1) Weigh 8 kg of large lithium cobaltate particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 550 g of cobalt hydroxide and 15 g of alumina; divide the above cobalt hydroxide into powder 1 with a mass of 150 g, powder 2 with a mass of 250 g, and powder 3 with a mass of 150 g; ball-mill and mix powder 2 with 15 g of alumina at a ball-mill speed of 200 revolutions per minute for 80 minutes to obtain powder 4; use powder 1 as additive one, powder 4 as additive two, and powder 3 as additive three;

[0066] (2) Put the weighed lithium cobaltate particles and additive one into the mixer and stir and mix them at a rotation speed of 400 revolutions per minute for 3 minutes to obtain the first mixture;

[0067] (3) Put additive two into the mixer and stir and mix it with the first mixture at a rotation speed of 1000 revolutions per minute for 20 minutes to obtain the second mixture;

[0068] (4) Put additive three into the mixer and stir and mix it with the second mixture at a rotation speed of 1600 revolutions per minute for 10 minutes to obtain the final mixture.

[0069] Comparative Example 1

[0070] A cathode material coating and mixing method, comprising the following steps:

[0071] (1) Weigh 8 kg of large lithium cobaltate particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 500 g of cobalt hydroxide and 15 g of alumina;

[0072] (2) Put all the weighed lithium cobaltate particles, cobalt hydroxide and alumina into the mixer, stir and mix them at a rotation speed of 400 revolutions per minute for 3 minutes, and then mix them at a rotation speed of 1600 revolutions per minute for 20 minutes to obtain the final mixture.

[0073] Comparative Example 2

[0074] A method for coating and mixing a cathode material, comprising the following steps:

[0075] (1) Weigh 8 kg of large lithium cobaltate particles with a particle size D50 = 17.5 μm and 2 kg of small particles with a particle size D50 = 5.2 μm; weigh 500 g of cobalt hydroxide and 15 g of alumina;

[0076] (2) Put all the weighed lithium cobaltate particles, cobalt hydroxide and alumina into a mixer, stir and mix at a speed of 400 revolutions per minute for 3 minutes, then mix at a speed of 1000 revolutions per minute for 20 minutes, and finally mix at a speed of 1600 revolutions per minute for 10 minutes to obtain the final mixed material.

[0077] Pour the final mixed materials obtained in Examples 1-5 and Comparative Examples 1-2 into mullite crucibles respectively and level them; put the above crucibles into a box furnace and bake at 900 °C; take out the baked materials and crush them to obtain samples. Test the mixed materials and the baked samples obtained in Examples 1-5 and Comparative Examples 1-2, and the test results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] Scanning electron micrographs of the mixed materials of Example 1, Comparative Example 1, and Comparative Example 2 are as Figure 1 shown; it can be seen from Figure 1 that in Comparative Example 1 and Comparative Example 2, the surface of the particles is more tightly wrapped, while the surface of the particles in Example 1 is more fluffy.

[0082] Charge-discharge curves of the baked samples of Example 1, Comparative Example 1, and Comparative Example 2 are as Figure 2 shown, and it can be seen from Figure 2 that the sample of Example 1 of the present invention has a better specific capacity.

[0083] EIS test results of the baked samples of Example 1, Comparative Example 1, and Comparative Example 2 are as Figure 3 shown, and it can be seen from Figure 3 that the sample of Example 1 of the present invention has a smaller impedance.

[0084] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention.

[0085] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material, characterized in that lithium cobaltate particles and a coating additive are weighed according to a certain ratio, the lithium cobaltate particles and the coating additive are put into a mixer, and are mixed through a low-speed stage, a medium-speed stage and a high-speed stage to obtain a final mixture; wherein, the coating additive is added in stages at the low-speed stage, the medium-speed stage and the high-speed stage respectively.

2. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material according to claim 1, characterized in that The coating additive is divided into three parts, namely additive one, additive two and additive three; specifically, the mixing process includes the following steps: (1) Put the lithium cobaltate particles and additive one into the mixer, stir and mix at a rotation speed of 150-500 rpm for 3-7 min to obtain mixture one; (2) Put additive two into the mixer, and stir and mix with the mixture one at a rotation speed of 900-1100 rpm for 20-35 min to obtain mixture two; (3) Put additive three into the mixer, and stir and mix with mixture two at a rotation speed of 1300-1600 rpm for 10-15 min.

3. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material according to claim 1, characterized in that, The lithium cobaltate particles include large particles with a D50 of 17-20 μm and small particles with a D50 of 4-7 μm.

4. A coating and mixing method for improving the room temperature capacity and impedance of a cathode material according to claim 3, characterized in that, The mass ratio of the large particles to the small particles is (3-5):

1.

5. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material according to claim 1, characterized in that The mass ratio of the lithium cobaltate particles to the coating additive is (15-30):

1.

6. The coating and mixing method for improving the room temperature capacity and impedance of the cathode material according to claim 2, characterized in that The mass ratio of additive one, additive two and additive three is (3.0-3.5):(5.0-5.5):(2-3).

7. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material according to claim 1, characterized in that The coating additive includes cobalt oxides or hydroxides.

8. A coating and mixing method for improving the room temperature capacity and impedance of a cathode material according to claim 2, characterized in that, Additive one, additive two or additive three further includes other element additives other than cobalt oxides or hydroxides, and the other element additives are selected from oxides or salts of at least one element among Al, Mg, Ti, Y, La, Ni, Mn, Zr, W, Mo.

9. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material according to claim 7, characterized in that, When additive one, additive two or additive three contains two or more additives, the two or more additives are mixed by ball milling, the ball milling speed is 200-500 rpm, and the ball milling time is 20-150 min.

10. A coating and mixing method for improving the normal temperature capacity and impedance of a cathode material according to claim 7, characterized in that The proportion of the other element additive in the total amount of the coating additive is 2%-3%.

Images