Dry multi-component coating method for high-nickel positive electrode material

Abstract

The application belongs to the technical field of lithium ion battery materials, and discloses a dry multi-component coating method for high-nickel positive electrode materials. Two-stage solid-phase material coating treatment is performed on the surface of the high-nickel positive electrode material, weak-acid solid-phase material is coated in the first stage, and alkaline oxide, hydroxide or neutral salt is coated in the second stage. The weak-acid solid-phase material coated in the first stage can not only reduce residual alkali content, but also form a tightly contacted coating layer on the surface of the high-nickel positive electrode material, so as to limit the dissolution of residual alkali and the damage of the substrate in subsequent operation processes; the coating in the second stage further forms a tightly transition layer on the surface of the positive electrode material, which is beneficial to lithium ion transmission and is also a protective structure; the heating temperature of the coating in the first stage and the coating in the second stage is relatively low, which is beneficial to saving heat energy cost.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to the coating modification of cathode materials. Background Technology

[0002] Currently, binary or multi-component precursor materials are generally prepared by co-precipitation. These precursor materials are then mixed with lithium salts and sintered at high temperatures to obtain the cathode material. Generally, the cathode material after a single sintering has a high residual alkali content on its surface, requiring alkali reduction.

[0003] In industrial production, there are two main ways to reduce residual alkali on the surface of cathode materials. One is to wash the material with water to dissolve and remove the residual alkali. The other is to first coat the cathode material and then perform high-temperature secondary or tertiary sintering, utilizing the principle that the residual alkali decomposes or reacts with the coating material to generate other substances at high temperatures to reduce the residual alkali on the surface.

[0004] Washing or high-temperature secondary and tertiary sintering of high-nickel cathode materials with water brings a series of problems: as the nickel content increases, the cathode material becomes less and less tolerant to the water environment, and surface phase transformation deteriorates. At the same time, lithium ions are lost through proton exchange reaction, resulting in a decrease in material capacity and a deterioration in structural stability. High-temperature secondary or tertiary sintering not only brings the problem of increased cost, but also makes it difficult for some coating reactions to be carried out in a high-temperature environment. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a dry multi-component coating method for high-nickel cathode materials.

[0006] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0007] After the precursor is mixed with lithium and sintered, a high-nickel cathode material is obtained. The surface of the high-nickel cathode material is subjected to a two-stage solid-phase coating treatment. In the first stage, a weakly acidic solid-phase material is coated, and in the second stage, an alkaline oxide, hydroxide, or neutral salt is coated.

[0008] Specifically, this invention provides a dry multi-component coating method for high-nickel cathode materials, comprising the following steps:

[0009] Step S1: Mix and activate the high-nickel cathode material with a weakly acidic solid phase in a mixing device with heat preservation function to obtain the primary material;

[0010] Step S2: The primary material is mixed with at least one of an alkaline oxide, a hydroxide, and a neutral salt to obtain a secondary material;

[0011] Step S3: Heat the secondary material to obtain a coated and modified high-nickel cathode material.

[0012] Furthermore, in some preferred embodiments of the present invention, the chemical formula of the high-nickel cathode material described in step S1 is LiNi. x Co y M (1-x-y) O2, where 0.8≤x<1, 0.04≤y<0.15, and M is at least one of Mn, Al, Zr, and Ti.

[0013] Furthermore, in some preferred embodiments of the present invention, the mass ratio of the high-nickel cathode material to the weakly acidic solid phase material in step S1 is 100:0.2~5.

[0014] Furthermore, in some preferred embodiments of the present invention, the mixing and activation temperature in step S1 is 80~250°C, and the time is 1~4h; the mixing equipment is a high-speed mixer or a rotary mixer.

[0015] Furthermore, in some preferred embodiments of the present invention, the weakly acidic solid substance is selected from at least one of boric acid, tungstic acid, molybdic acid, silicic acid, aluminum dihydrogen phosphate, ammonium nitrate, ammonium dihydrogen phosphate, and phosphotungstic acid.

[0016] Furthermore, in some preferred embodiments of the present invention, the alkaline oxide is selected from at least one of alumina, titanium dioxide, cobalt oxide, zirconium oxide, and cerium dioxide; the hydroxide is selected from at least one of aluminum hydroxide and cobalt hydroxyoxide; and the neutral salt is selected from at least one of aluminum fluoride, cerium fluoride, and aluminum phosphate.

[0017] Furthermore, in some preferred embodiments of the present invention, the mass of the alkaline oxide, hydroxide, and neutral salt added in step S2 is 0.5 to 3% of the mass of the high-nickel cathode material in step S1.

[0018] Furthermore, in some preferred embodiments of the present invention, the heating temperature in step S3 is 250~680°C, and the heating time is 2~8h.

[0019] This invention employs a purely dry coating method. First, a weakly acidic solid phase is coated onto the surface of a high-nickel cathode material. At a relatively low mixing and activation temperature, the weakly acidic solid phase forms a coating layer on the substrate surface. During activation, the coating undergoes a certain degree of dehydration, which facilitates a tighter bond with the substrate material. Next, other substances are coated onto the surface of the high-nickel cathode material. Building upon the first stage of coating, the weakly acidic solid phase reacts with residual alkali on the cathode material's surface. During subsequent heat treatment, the water loss through neutralization further promotes the formation of a tight contact interface. This coating layer also serves as a protective layer for the material surface during subsequent coating and heat treatment processes, reducing damage to the substrate from subsequent heat treatment operations. After the second stage of coating, heat treatment can be performed at a relatively low temperature to obtain a double-layer coated high-nickel cathode material. The coating layer forms a protective structure for the cathode material, does not increase the soluble lithium content on the material surface, and serves as a tight transition layer that facilitates lithium-ion transport.

[0020] Compared with the prior art, the present invention has the following obvious beneficial technical effects:

[0021] (1) A low level of soluble lithium can be achieved in high-nickel cathode materials without water washing;

[0022] (2) The dry coating process will not damage the structure of the high-nickel cathode material;

[0023] (3) The dry coating process is carried out in two stages. The weakly acidic solid material coated in the first stage can not only reduce the residual alkali content, but also form a tightly contacted coating layer on the surface of the high-nickel cathode material, which limits the dissolution of residual alkali and the damage to the substrate by subsequent operations. The coating in the second stage further forms a tight transition layer on the surface of the cathode material that is conducive to lithium ion transport, and also serves as a protective structure. The heating temperatures of the first and second stages of coating are both low, which helps to save thermal energy costs.

[0024] (4) The coating modification process is relatively simple, the process parameters are controllable, and it can be applied on a large scale in industry. Attached Figure Description

[0025] Figure 1 The images shown are SEM images of the high-nickel cathode material before and after coating in Example 1. (a) is the SEM image of the high-nickel cathode material before coating, (b) is the SEM image of the material after coating with a weakly acidic solid phase, and (c) is the SEM image of the finished product.

[0026] Figure 2 The graphs show the cycle performance of batteries using the products obtained in Example 1 and Comparative Examples 1-3 as the positive electrode active material. Detailed Implementation

[0027] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0028] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0030] This invention performs a two-stage solid-phase coating treatment on the surface of a high-nickel cathode material. In the first stage, a weakly acidic solid-phase material is coated, and in the second stage, an alkaline oxide, hydroxide, or neutral salt is coated.

[0031] The weakly acidic solid substance is selected from at least one of boric acid, tungstic acid, molybdic acid, silicic acid, aluminum dihydrogen phosphate, ammonium nitrate, ammonium dihydrogen phosphate, and phosphotungstic acid.

[0032] The alkaline oxide is selected from at least one of aluminum oxide, titanium dioxide, cobalt oxide, zirconium oxide, and cerium dioxide.

[0033] The hydroxide is selected from at least one of aluminum hydroxide and cobalt hydroxyoxide; the neutral salt is selected from at least one of aluminum fluoride, cerium fluoride, and aluminum phosphate.

[0034] In the first stage of the coating process, the reaction temperature (mixing and activation) is controlled at 80~250℃, which can be 80℃, 100℃, 150℃, 200℃, 220℃, 250℃, etc.; the reaction time (mixing and activation) is controlled at 1~4h, which can be 1h, 2h, 3h, 4h, etc.

[0035] After the two-stage coating is completed, sintering is carried out, and the sintering temperature is controlled at 250~680℃, which can be 280℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 680℃, etc.; the sintering time is controlled at 2~8h, which can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, etc.

[0036] The weakly acidic solid material coated in the first stage can not only reduce the residual alkali content, but also form a tightly contacted coating layer on the surface of the high-nickel cathode material, limiting the dissolution of residual alkali and the damage to the matrix caused by subsequent operations; the second stage coating further forms a tight transition layer on the surface of the cathode material that is conducive to lithium-ion transport, and also serves as a protective structure.

[0037] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0038] Example 1

[0039] (1) Weigh 8000g of high-nickel cathode material (NCM90 / 5 / 5), 128g of tungstic acid (tungsten trioxide with crystal water), and 45.76g of boric acid, add them to a small VC mixer, control the temperature inside the mixer at 80℃ by jacket insulation, stir at low speed for 2h to obtain a primary mixture.

[0040] (2) Collect the primary mixture, weigh 5000g, add it to a small conventional high-speed mixer, add 47.32g of cobalt hydroxide and 28.9g of aluminum hydroxide, mix for 30min to obtain the secondary coating.

[0041] (3) Take a certain mass of secondary coating material and heat treat it in a muffle furnace at a constant temperature of 350℃ for 6 hours to obtain the coated finished product.

[0042] Figure 1 The images show SEM images of the high-nickel cathode material at different stages. As can be seen from the images, after the first coating, a relatively thin and uniform coating layer forms on the material surface; after the second coating, the coating layer on the material surface becomes thicker, and the primary particle morphology of the high-nickel substrate becomes difficult to discern; this indicates that after the two coating processes, two uniform coating layers are formed on the material surface.

[0043] The residual alkali content in the coated finished product was tested, and the results showed that the residual amount of lithium hydroxide was 0.5361% and the residual amount of lithium carbonate was 0.2326%.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 1 is that step (2) is omitted, i.e.:

[0046] (1) Weigh 8000g of high-nickel cathode material (NCM90 / 5 / 5) after washing and drying, 128g of tungstic acid (tungsten trioxide with water of crystallization), and 45.76g of boric acid, add them to a small VC mixer, and mix for 30min under non-constant temperature conditions to obtain a mixture.

[0047] (2) Take a certain mass of the primary mixture described in (1) and heat treat it in a muffle furnace at a constant temperature of 350°C for 6 hours to obtain the coated finished product.

[0048] Comparative Example 2

[0049] The difference between Comparative Example 2 and Example 1 is that the first stage of coating tungstic acid and boric acid was not performed, i.e.:

[0050] (1) Weigh 5000g of water-washed and dried high-nickel cathode material (NCM90 / 5 / 5), add it to a small conventional high-speed mixer, add 28.95g of cobalt hydroxide and 17.68g of aluminum hydroxide, stir and mix for 30min to obtain the coating.

[0051] (2) Take a certain mass of the coating material described in (1) and heat treat it in a muffle furnace at a constant temperature of 350°C for 6 hours to obtain the finished coating product.

[0052] Comparative Example 3

[0053] The difference between Comparative Example 3 and Example 1 is that the order of the first-stage coating and the second-stage coating is reversed, that is:

[0054] (1) Weigh 8000g of high-nickel cathode material (NCM90 / 5 / 5) after one sintering and pulverization, 128g of tungstic acid (containing tungsten trioxide with water of crystallization), add them to a small VC mixer, and mix for 30min under non-constant temperature conditions to obtain a mixture.

[0055] (2) Collect the primary mixture, weigh 5000g, add it to a small conventional high-speed mixer, add 47.32g of cobalt hydroxide and 28.9g of aluminum hydroxide, mix for 30min to obtain the secondary coating.

[0056] (3) Take a certain mass of secondary coating material and heat treat it in a muffle furnace at a constant temperature of 550℃ for 6 hours to obtain the coated finished product.

[0057] The finished products obtained in Example 1 and Comparative Examples 1-3 were assembled into batteries according to the following method: The positive electrode material was homogenized with a ratio of positive active material: conductive agent: binder = 90:5:5. The conductive agent and binder were SUPER-P and PVDF, respectively. After coating, drying, rolling, stamping, weighing, vacuum drying and other operations, a dried electrode sheet was obtained. Half cells were assembled using CR2430 button cells for testing. The counter electrode was a lithium sheet. The capacity test regime was 2.8-4.25V@room temperature, 0.2C current. Subsequently, room temperature cycling test was carried out, and the charge and discharge current was 1C / 1C.

[0058] Battery cycle performance results are as follows Figure 2 As shown, it can be seen that the battery using the cathode material prepared in Example 1 as the active material has the highest capacity retention rate after 70 cycles, which also shows that the coating method of the cathode material described in this invention has a very high value for the application of cathode materials in batteries.

[0059] Example 2

[0060] (1) Weigh 150 kg of NCM95 / 3 / 2 sintered matrix and 2.8 kg of phosphotungstic acid, add them to a single cone mixer, control the temperature inside the mixer at 100℃ by jacket insulation, stir at low speed for 4 hours to obtain a primary mixture.

[0061] (2) Collect the primary mixture, weigh 8000g, add it to a small conventional high-speed mixer, add 74.9g of cobalt hydroxyoxide and 12.4g of cerium fluoride, stir and mix for 25min to obtain the secondary coating.

[0062] (3) Take a certain mass of secondary coating material and heat treat it in a box furnace at 450℃ for 8 hours to obtain the coated finished product.

[0063] Example 3

[0064] (1) Weigh 150 kg of NCM93 / 7 / 1 sintered matrix material and 0.5 kg of aluminum dihydrogen phosphate, add them to the high-speed mixer, control the temperature inside the mixer at 150℃ by jacket insulation, stir at low speed for 2 hours to obtain a primary mixture.

[0065] (2) Collect the primary mixture, weigh 8000g, add it to a small conventional high-speed mixer, add 80g of aluminum phosphate and 55g of aluminum fluoride, stir and mix for 25min to obtain the secondary coating.

[0066] (3) Take a certain mass of secondary coating material and heat treat it in a box furnace at 450℃ for 8 hours to obtain the coated finished product.

[0067] Example 4

[0068] (1) Weigh 100kg of NCM92 / 6 / 2 sintered matrix material and 0.8kg of molybdic acid, add them to a high-speed mixer, control the temperature inside the mixer at 200℃ by jacket insulation, stir at low speed for 3h to obtain a primary mixture.

[0069] (2) Collect the primary mixture, weigh 8000g, add it to a small conventional high-speed mixer, add 60g of cobalt hydroxide and 45g of titanium dioxide, stir and mix for 30min to obtain the secondary coating.

[0070] (3) Take a certain mass of secondary coating material and heat treat it in a box furnace at 500℃ for 8 hours to obtain the coated finished product.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dry multi-component coating method for high-nickel cathode materials, characterized in that, Includes the following steps: Step S1: The high-nickel cathode material and a weakly acidic solid phase are mixed and activated in a mixing device with heat preservation function to obtain a primary material; the mixing and activation temperature is 80~220℃ and the time is 1~4h; the weakly acidic solid phase is selected from at least one of boric acid, tungstic acid, molybdic acid, silicic acid, aluminum dihydrogen phosphate, ammonium nitrate, ammonium dihydrogen phosphate, and phosphotungstic acid; Step S2: The primary material is mixed with at least one of an alkaline oxide, a hydroxide, and a neutral salt to obtain a secondary material; the alkaline oxide is selected from at least one of alumina, titanium dioxide, cobalt oxide, zirconium oxide, and cerium dioxide; the hydroxide is selected from at least one of aluminum hydroxide and cobalt hydroxide; the neutral salt is selected from at least one of aluminum fluoride, cerium fluoride, and aluminum phosphate. Step S3: Heat the secondary material to obtain a coated and modified high-nickel cathode material; the heating temperature is 250~680℃ and the heating time is 2~8h.

2. The dry multi-component coating method for high-nickel cathode materials as described in claim 1, characterized in that, The chemical formula of the high-nickel cathode material mentioned in step S1 is LiNi. x Co y M (1-x-y) O2, where 0.8≤x<1, 0.04≤y<0.15, and M is at least one of Mn, Al, Zr, and Ti.

3. The dry multi-component coating method for high-nickel cathode materials as described in claim 1 or 2, characterized in that, The mass ratio of the high-nickel cathode material to the weakly acidic solid phase material in step S1 is 100:0.2~5.

4. The dry multi-component coating method for high-nickel cathode materials as described in claim 1, characterized in that, The mixing equipment mentioned in step S1 is a high-speed mixer or a rotary mixer.

5. The dry multi-component coating method for high-nickel cathode materials as described in claim 1, characterized in that, The mass of the alkaline oxide, hydroxide, and neutral salt added in step S2 is 0.5 to 3% of the mass of the high-nickel cathode material in step S1.

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