A method for reducing residual alkali on the surface of high-nickel positive electrode material

Abstract

The present invention provides a method for reducing residual alkali on the surface of high-nickel positive electrode materials. This method involves loading an acid onto a carrier and then mixing it with the high-nickel positive electrode material to produce a mixture. The mixture is then subjected to heat sublimation to obtain a high-nickel positive electrode material with reduced residual alkali. Compared to traditional water-washing processes for reducing residual alkali on the surface, this method is more environmentally friendly and causes less damage to the positive electrode material. The resulting material has lower total alkali content and a smaller specific surface area. The resulting battery exhibits improved specific capacity, rate capability, and cycle performance.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for reducing residual alkali on the surface of a high-nickel positive electrode material. Background Art

[0002] Lithium-ion batteries, due to their excellent electrochemical properties, are widely used in 3C digital products, power tools, electric vehicles, energy storage, and military and aerospace applications. Among lithium-ion battery cathode materials, high-nickel cathode materials are more popular in applications such as electric vehicles due to their higher capacity, leading to increasing research on these materials.

[0003] However, due to the high residual alkali on the surface of high-nickel positive electrode materials, side reactions are likely to occur during battery use, resulting in a decrease in the cycle life of the battery. Therefore, in the existing production process, the high-nickel positive electrode materials are washed with water, and the residual alkali on the surface of the positive electrode materials after washing can be greatly reduced. However, the surface of the positive electrode material after washing will be damaged by water, resulting in a deterioration in the cycle performance of the battery. At the same time, washing will also increase the BET of the material, which has a great impact on the performance of the positive electrode material. Therefore, it is urgent to find a new method to reduce the residual alkali on the surface, thereby reducing the damage caused by washing to the high-nickel positive electrode material and improving the performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present application is to provide a method for reducing residual alkali on the surface of high-nickel positive electrode materials. While achieving the purpose of reducing residual alkali, the method also avoids the introduction of other substances and does not damage the surface of the positive electrode material.

[0005] To achieve the above invention objectives, the present invention removes residual alkali on the surface by mixing an acid-containing carrier with the positive electrode material, and then uses the high-temperature sublimation principle to sublimate and remove the acid carrier. The specific technical solution is as follows:

[0006] A method for reducing residual alkali on the surface of a high-nickel positive electrode material, the method comprising the following steps:

[0007] S1: After the acid is loaded on the carrier, it is mixed with the high-nickel positive electrode material to obtain a mixture;

[0008] S2: heating and sublimating the mixture to obtain a high-nickel positive electrode material with reduced residual alkali content.

[0009] During the heating sublimation treatment process described in S2 of the present invention, heated inert gas or dry air is introduced. After mixing, the carrier is evenly distributed in the material. As the high-temperature gas is introduced, the temperature of the mixed material rises rapidly, and the carrier sublimates rapidly. The carrier is not damaged by the thermal sublimation process. Compared with the traditional water washing process to remove residual alkali, this method avoids the water and hydrogen ions entering the surface of the positive electrode material during water washing and damaging the material surface. At the same time, the lithium salt generated by the reaction of acid and residual alkali remains on the surface of the positive electrode material, which can also increase the conductivity and have better rate and cycle performance.

[0010] In the present invention, the carrier described in S1 is a substance having a sublimation temperature of 40°C-500°C, preferably a substance having a sublimation temperature of 100°C-300°C, and more preferably one or more of adamantane, p-benzoquinone, and 1,3-cyclohexanedione. Among them, some carriers, such as adamantane, have a sublimation temperature of 180°C-192°C, p-benzoquinone has a sublimation temperature of 293°C, and 1,3-cyclohexanedione has a sublimation temperature of approximately 170.05°C.

[0011] In one embodiment, the particle size of the carrier is one or more of nanometer, micrometer, and millimeter. Preferably, the particle size of the carrier is nanometer and / or micrometer. Particle sizes other than micro- and nanometer sizes can also achieve the above-mentioned sublimation effect, but micro- and nanometer sizes are more conducive to process control.

[0012] In the present invention, the acid described in S1 is one or more of an inorganic oxygen-containing acid, an inorganic non-oxygen-containing acid and an organic acid, preferably one or more of an inorganic oxygen-containing acid, an inorganic non-oxygen-containing acid, formic acid, and acetic acid, and more preferably one or more of hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid; preferably, the mass ratio of the acid to the carrier is (0.002-0.04):1, preferably (0.01-0.02):1.

[0013] In one embodiment, the concentration of the acid may preferably be 5 wt%-38 wt%. Of course, acids outside this range may also meet the requirements.

[0014] In the present invention, the chemical formula of the high nickel cathode material described in S1 is LiNi w Co x Mn y M zO2, wherein M is one or more of the elements Zr, Al, W, Ce, B, Mg, Ti, F, Sb, Sn, Sr, and Y, and the above-mentioned M elements are all commonly used added metal elements of the positive electrode material, and z is the sum of the molar ratios of the M elements; wherein 0.5≤w<1, 0<x<1, 0<y<1, 0≤z<1, and w+x+y+z=1, preferably wherein 0.5≤w<1, 0<x<0.5, 0<y<0.6, 0≤z<0.3, and w+x+y+z=1; preferably, the mass ratio of the high nickel positive electrode material to the acid-free carrier is (1-20):1, preferably (2-10):1, and more preferably (4-5):1.

[0015] In the present invention, the mixing process in S1 is one or more of fluidization, stirring, vibration, and spray mixing; preferably, the mixing time is 0.1-3 hours, preferably 0.3-1 hour.

[0016] In the present invention, the temperature of the heating sublimation treatment in S2 is greater than or equal to the sublimation temperature of the carrier, and the temperature of the heating sublimation treatment is preferably 40°C-500°C, more preferably 100°C-300°C.

[0017] In the present invention, the time of the heating sublimation treatment in S2 is 0.1-3 hours, preferably 0.3-1 hour.

[0018] In the present invention, the atmosphere during the heating sublimation treatment in S2 is an inert atmosphere and / or dry air, preferably an inert atmosphere and / or dry air from which carbon dioxide has been removed, and more preferably one or more of an inert gas, nitrogen, and dry air from which carbon dioxide has been removed.

[0019] Another object of the present invention is to provide a high-nickel positive electrode material with reduced surface residual alkali.

[0020] A high nickel cathode material with low surface residual alkali prepared by the above method, wherein the mass content of total alkali on the surface of the high nickel cathode material is less than 5000ppm and the specific surface area range is less than 0.5m 2 The mass content of the total surface alkali is calculated based on the total mass of the alkaline lithium compounds on the surface of the high-nickel positive electrode material, preferably based on the total mass of lithium hydroxide and / or lithium carbonate on the surface of the high-nickel positive electrode material.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Compared with the traditional water washing process to remove residual alkali, the method of the present invention avoids the water and hydrogen ions entering the surface of the positive electrode material during water washing to damage the material surface. The lithium salt generated by the reaction of acid and residual alkali remains on the surface of the positive electrode material and can also increase the conductivity, thereby having better rate and cycle performance.

[0023] (2) No waste liquid or other impurities are generated during the removal of residual alkali, which is more environmentally friendly than the water washing process. DETAILED DESCRIPTION

[0024] The preparation method of the present invention is further explained below by more specific examples, but does not constitute any limitation.

[0025] The main raw materials used in the following examples and comparative examples are as follows

[0026] Lithium nickel cobalt manganese oxide LiNi 0.75 Co 0.1 Mn 0.1 Sr 0.05 O2、LiNi 0.7 Co 0.1 Mn 0.1 Ti 0.1 O2、LiNi 0.7 Co 0.05 Mn 0.05 W 0.1 Ce 0.1 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2, battery grade, Wanhua Chemical;

[0027] Hydrochloric acid, 10 wt.% in H2O, FCC, Aladdin;

[0028] Nitric acid, 10% (v / v), Aladdin;

[0029] Phosphoric acid, 15% w / w, Aladdin;

[0030] Acetic acid, GR, 99.8%, Aladdin;

[0031] The acids in the examples are all diluted as needed;

[0032] Nitrogen, 99.999%, Linde Gas;

[0033] Adamantane, 99%, Aladdin;

[0034] p-Benzoquinone, >98.0%, Aladdin;

[0035] 1,3-Cyclohexanedione, >98%, Aladdin.

[0036] The relevant performance test methods of high nickel precursor materials are as follows:

[0037] Electrochemical testing equipment, Shenzhen Xinwei button battery testing system;

[0038] Residual alkali test, Swiss Metrohm potentiometric titrator, Swiss Metrohm 905, GBT41704-2022;

[0039] Specific surface area test, Quantachrome Instruments, Quadrasorb evoTM-KP / MP, test standard (GB / T19587-2017);

[0040] For the above-mentioned particles of adamantane, p-benzoquinone, 1,3-cyclohexanedione, etc. with a particle size of more than millimeters, first use a roller crusher to crush the particles, set the roller gap to 0.5mm, and the roller speed to 15Hz to obtain a powder with D50 = 0.5-1mm. Then use a jet mill with a cyclone separator to crush the material. The jet mill crushing pressure is 0.2MPa, the feeding frequency is 5Hz, the classification frequency is 30Hz, and the induced draft frequency is 40Hz. Take the material in the cyclone separator to obtain a powder with D50 = 1-100 microns; for the above-mentioned The powder with D50 = 0.5-1mm after the roller is crushed by a jet mill with a cyclone separator. The jet mill pressure is 0.8MPa, the feeding frequency is 5Hz, the classification frequency is 50Hz, and the induced draft frequency is 20Hz. The material from the cyclone separator is added back into the grinder for crushing. After crushing, the material below the bag dust collector is taken. This part of the material is ultrafine powder, and this part of the material is D50 = 200-800 nanometers. The above-mentioned roller machine model is Suzhou Xiran XRCA-235-2S, and the above-mentioned jet mill model is Germany Netzsch CGS10.

[0041] Example 1

[0042] S1: Add 5g of D50=500 nanometer diamond powder to 1g of 15wt% hydrochloric acid solution, mix well and set aside;

[0043] 6g of the acid-containing nano-diamondane powder mixed with the acid solution was mixed with the positive electrode material (LiNi 0.75 Co 0.1 Mn 0.1 Sr 0.05 O2) mixed, the positive electrode material is 100g, the mixed material is shaken and mixed for 0.5h, the water and carbon dioxide generated by the reaction are discharged with the tail gas, and lithium chloride remains on the surface of the high nickel positive electrode material;

[0044] S2: Heated nitrogen gas was introduced into a mixing and vibration drying apparatus at a nitrogen source pressure of 10 kPa (gauge pressure), a gas flow rate of 1 L / min, and a gas temperature of 190°C to sublimate the mixture. After 0.2 h, the adamantane was completely sublimed, yielding a high-nickel cathode material with reduced residual alkali content. Characterization results for the resulting high-nickel cathode material with low surface residual alkali content are shown in Tables 1 and 2.

[0045] Example 2

[0046] S1: Add 10 g of p-benzoquinone powder (D50 = 10 μm) to 3 g of 5 wt% acetic acid solution, mix well and set aside;

[0047] 13g of acid-containing p-benzoquinone powder mixed with acid solution was mixed with positive electrode material (LiNi 0.7 Co 0.1 Mn 0.1 Ti 0.1 O2) mixed, the positive electrode material is 100g, the material is added to the vibration mixing and drying equipment and vibrated for 1h, the mixing equipment speed is 30Hz, the water and carbon dioxide generated by the reaction are discharged with the tail gas, and the lithium acetate remains on the surface of the high nickel positive electrode material, which can help the material to conduct electricity and repair the surface of the material at the same time;

[0048] S2: Heat the material to 295°C by introducing compressed air depleted of carbon dioxide at a source pressure of 10 kPa (gauge) and a flow rate of 1 L / min. Sublimation treatment was performed on the mixture. After 1 hour, the sublimation of p-benzoquinone was complete, resulting in a high-nickel cathode material with reduced residual alkali content. Characterization results for the resulting high-nickel cathode material with low surface residual alkali content are shown in Tables 1 and 2.

[0049] Example 3

[0050] S1: Add 50 g of 1,3-cyclohexanedione powder (D50 = 1 mm) to 0.5 g of 38 wt% phosphoric acid solution, mix well and set aside;

[0051] 50.5 g of the acid-containing 1,3-cyclohexanedione powder mixed with the acid solution was mixed with the positive electrode material (LiNi 0.7 Co 0.05 Mn 0.05 W 0.1 Ce 0.1 O2) mixed, the positive electrode material is 100g, the mixed material is added to the stirring mixing and drying equipment and mixed at room temperature for 2h, the mixing equipment speed is 25Hz, the carbon dioxide generated by the reaction is discharged with the tail gas, and the lithium phosphate remains on the surface of the high nickel positive electrode material, which can help the material to conduct electricity and repair the surface of the material at the same time;

[0052] S2: Heated nitrogen gas was introduced at a source pressure of 10 kPa (gauge pressure) and a flow rate of 1 L / min. The material was heated to 180°C and sublimated. After 3 hours, the 1,3-cyclohexanedione sublimed completely, resulting in a high-nickel cathode material with reduced residual alkali content. Characterization results for the obtained high-nickel cathode material with low surface residual alkali content are shown in Tables 1 and 2.

[0053] Example 4

[0054] S1: Add 10 g of D50 = 5 micron adamantane powder to 4 g of 5 wt% nitric acid solution, mix well and set aside;

[0055] 14 g of the adamantane powder mixed with the acid solution was mixed with the positive electrode material (LiNi 0.5 Co 0.2 Mn 0.3 O2) mixed, the positive electrode material is 100g, the mixed material is added to the fluidized drying equipment and mixed for 1h at room temperature, the vibration frequency is 25Hz, the water and carbon dioxide generated by the reaction are discharged with the tail gas, and the lithium nitrate remains on the surface of the high nickel positive electrode material, which can help the material to conduct electricity and repair the surface of the material at the same time;

[0056] S2: The mixture was sublimed through a fluidized bed dryer, with heated argon and nitrogen at a source pressure of 10 kPa (gauge pressure), a gas flow rate of 1 L / min, and a gas temperature of 190°C. After 1 hour, the adamantane was completely sublimed, yielding a high-nickel cathode material with reduced residual alkali content. Characterization results for the resulting high-nickel cathode material with low surface residual alkali content are shown in Tables 1 and 2.

[0057] Comparative Example 1

[0058] This comparative example is an existing technology for reducing surface residual alkali. It includes the following steps:

[0059] (1) Add 100g of positive electrode material (LiNi 0.7 Co 0.1 Mn 0.1 Ti 0.1 O2), stirred by a stirring paddle at a speed of 40 Hz, and taken out after stirring for 3 minutes;

[0060] (2) The washed material is filtered and placed in an oven for drying at a drying temperature of 185° C., a vacuum degree of -0.08 MPa, and a drying time of 3 h. After drying, a positive electrode material with reduced surface residual alkali is obtained.

[0061] The characterization results of the obtained cathode materials are shown in Tables 1 and 2.

[0062] Comparative Example 2

[0063] This comparative example is an existing technology for reducing surface residual alkali. It includes the following steps:

[0064] (1) Add 100g of positive electrode material (LiNi 0.5 Co 0.2 Mn 0.3 O2), stirred by a stirring paddle at a speed of 30 Hz, and taken out after stirring for 3 minutes;

[0065] (2) The washed material is filtered and placed in an oven for drying at a drying temperature of 185° C., a vacuum degree of -0.08 MPa, and a drying time of 3 h to obtain a positive electrode material with reduced surface residual alkali;

[0066] The characterization results of the obtained cathode materials are shown in Tables 1 and 2.

[0067] The positive electrode materials after reducing the residual alkali obtained in the above Examples 1-4 and Comparative Examples 1 and 2 were assembled with a button battery, and the electrochemical performance of the assembled button battery was tested. The tested performance included 0.2C capacity, 2C / 0.2C rate performance, 2C cycle 50-cycle performance, the discharge cutoff voltage of the test was 2.5V, and the charge cutoff voltage was 4.25V. At the same time, a surface residual alkali content test and a BET test were also carried out. The electrochemical performance test results are listed in Table 1, and the surface residual alkali content and BET test results are listed in Table 2.

[0068] Table 1 Electrochemical performance test results

[0069] Serial number 0.2C discharge specific capacity Magnification 2C / 0.2C 50-week cycle retention rate Example 1 217.92 91.17％ 99.13％ Example 2 215.92 91.11％ 98.88％ Example 3 214.99 90.95％ 98.72％ Example 4 164.38 92.79％ 99.46％ Comparative Example 1 213.42 89.60％ 94.66％ Comparative Example 2 164.68 91.31％ 96.57％

[0070] Table 2 Surface residual alkali content and BET test results

[0071]

[0072]

[0073] The results in Tables 1 and 2 show that the preparation method provided in the present application can indeed reduce the residual alkali on the surface of the high-nickel positive electrode material, and compared with the use of the traditional water washing process to remove the residual alkali in Comparative Example 1, the method of the present application avoids the damage to the surface of the material by water washing, and the obtained positive electrode material has lower residual alkali and a smaller specific surface area, and the battery prepared has better discharge capacity, rate performance and cycle performance.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0075] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the present invention and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for reducing residual alkali on the surface of a high-nickel positive electrode material, characterized in that: The method comprises the following steps: S1: After the acid is loaded on the carrier, it is mixed with the high-nickel positive electrode material to obtain a mixture; S2: heating and sublimating the mixture to obtain a high-nickel positive electrode material with reduced residual alkali content; Wherein, the carrier described in S1 is a substance with a sublimation temperature of 40°C-500°C; Wherein, the temperature of the heating sublimation treatment in S2 is greater than or equal to the sublimation temperature of the carrier.

2. The method according to claim 1, wherein S1 The carrier is a material with a sublimation temperature of 100°C-300°C.

3. The method according to claim 2, wherein S1 The carrier is one or more of adamantane, p-benzoquinone, and 1,3-cyclohexanedione; The particle size of the carrier is one or more of nanometer scale, micrometer scale and millimeter scale.

4. The method according to claim 3, wherein The particle size of the carrier S1 is nanometer and / or micrometer scale.

5. The method according to claim 1 or 2, wherein: The acid in S1 is one or more of an inorganic oxygen-containing acid, an inorganic non-oxygen-containing acid and an organic acid.

6. The method according to claim 5, wherein The acid in S1 is one or more of an inorganic oxygen-containing acid, an inorganic non-oxygen-containing acid, formic acid, and acetic acid; The mass ratio of the acid to the carrier is (0.002-0.04):

1.

7. The method according to claim 6, wherein The acid in S1 is one or more of hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid; The mass ratio of the acid to the carrier is (0.01-0.02):

1.

8. The method according to claim 1 or 2, wherein: The chemical formula of the high nickel cathode material in S1 is LiNi w Co x Mn y M z O2, wherein M is one or more of the elements Zr, Al, W, Ce, B, Mg, Ti, F, Sb, Sn, Sr, Y, wherein 0.5≤w<1, 0<x<1, 0<y<1, 0≤z<1, and w+x+y+z=1.

9. The method according to claim 8, wherein In the high nickel positive electrode material of S1, 0.5≤w<1, 0<x<0.5, 0<y<0.6, 0≤z<0.3, and w+x+y+z=1; The mass ratio of the high-nickel positive electrode material to the acid-free carrier is (1-20):

1.

10. The method according to claim 9, wherein The mass ratio of the high nickel positive electrode material in S1 to the acid-free carrier is (2-10):

1.

11. The method according to claim 10, wherein The mass ratio of the high nickel positive electrode material in S1 to the acid-free carrier is (4-5):

1.

12. The method according to claim 1 or 2, wherein: The mixing process described in S1 is one or more of fluidization, stirring, vibration, and spray mixing.

13. The method according to claim 12, wherein: The mixing treatment time in S1 is 0.1-3 hours.

14. The method according to claim 13, wherein The mixing treatment time in S1 is 0.3-1 h.

15. The method according to claim 1 or 2, wherein: The temperature of the heating sublimation treatment in S2 is 40°C-500°C; And / or, the heating sublimation treatment time in S2 is 0.1-3h; And / or, the atmosphere during the heating sublimation treatment in S2 is an inert atmosphere and / or dry air.

16. The method according to claim 15, wherein The temperature of the heating sublimation treatment in S2 is 100°C-300°C; And / or, the heating sublimation treatment time in S2 is 0.3-1h; And / or, the atmosphere during the heating sublimation treatment in S2 is an inert atmosphere and / or dry air from which carbon dioxide has been removed.

17. The method according to claim 16, wherein The atmosphere during the heating sublimation treatment in S2 is one or more of an inert gas, nitrogen, and dry air from which carbon dioxide has been removed.

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