Preparation method for improving storage and gas production performance of ternary positive electrode material

Abstract

A preparation method for a ternary positive electrode material having a coating layer, which method comprises the following steps: S1, mixing a ternary material precursor with a lithium source, pre-sintering same to obtain a pre-sintered material, mixing the pre-sintered material again, and then calcining same, so as to obtain a primary ternary positive electrode material; S2, dissolving an additive T to obtain a solution U, subjecting the primary ternary positive electrode material and the solution U to mixing and washing, and drying same, so as to obtain a secondary ternary positive electrode material; and S3, subjecting the secondary ternary positive electrode material to an atomic layer deposition treatment, so as to obtain a ternary positive electrode material, wherein the additive T is composed of a lithium-containing material and a sodium-containing material, and the stirring Reynolds number during the process of washing is 200-20000. Further disclosed are a ternary positive electrode material prepared according to the method, and a lithium-ion battery.

Description

A preparation method for improving storage and gas production performance of ternary positive electrode materials Technical Field

[0001] The present disclosure belongs to the technical field of lithium-ion batteries, and particularly relates to a preparation method for improving the storage and gas production performance of a ternary positive electrode material. Background Art

[0002] Ternary batteries with high energy density, good cycle life, environmental friendliness and no memory effect have rapidly attracted market attention due to their excellent comprehensive performance. Ultra-high nickel ternary positive electrode materials have received widespread attention worldwide due to their high energy density. In the preparation process of ultra-high nickel ternary materials, in order to prevent the formation of divalent nickel and reduce the degree of lithium-nickel mixing, the amount of lithium is usually increased to make the lithium source excessive. Excessive lithium will generate excessive residual lithium on the surface of the material during the sintering process, which is prone to gelation during the battery manufacturing process, resulting in the inability to coat. Even if the battery is successfully made, the residual lithium will react with the electrolyte during the cycle, causing the material storage performance to deteriorate and even produce excessive gas, affecting the battery safety performance.

[0003] Currently, water washing is commonly used to reduce residual lithium on the surface of materials. The intensity of water washing has a significant impact on residual lithium. If the water washing intensity is insufficient, the residual lithium cannot be washed away, affecting battery safety performance. If the water washing intensity is too high, the surface lattice lithium will be washed out while the residual lithium on the surface is washed away, and may cause primary particles to fall out, affecting battery capacity. In this process, the residual lithium acts as a binder. If the binder is excessively washed away, some primary particles on the surface of the material will not be able to adhere to the material surface. Therefore, it is necessary to control the water washing intensity and increase the compactness between the material particles to ensure the water washing effect.

[0004] Ultra-high nickel materials, due to their high nickel content, are extremely sensitive to water. During water washing, lattice lithium is easily washed out. This high nickel content also inherently disadvantages ultra-high nickel materials in terms of gas production and storage performance compared to low-nickel materials.

[0005] Summary of the Invention

[0006] The present disclosure aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present disclosure proposes a preparation method for improving the storage and gas production performance of ternary positive electrode materials, which can optimize the storage and gas production performance.

[0007] According to a first aspect of the present disclosure, a method for preparing a ternary cathode material having a coating layer is proposed, comprising the following steps:

[0008] S1: mixing a ternary material precursor with a lithium source and pre-calcining the mixture to obtain a pre-calcined material, and then mixing the pre-calcined material again and calcining the mixture to obtain a primary ternary positive electrode material;

[0009] S2: dissolving the additive T to obtain a solution U, mixing the primary ternary cathode material with the solution U, washing the mixture, and drying the mixture to obtain a secondary ternary cathode material;

[0010] S3: performing atomic layer deposition on the secondary ternary cathode material to obtain a ternary cathode material;

[0011] The additive T is composed of lithium-containing material and sodium-containing material;

[0012] During the washing process, the stirring Reynolds number is 200 to 20,000.

[0013] The stirring Reynolds number is controlled by adjusting the size of the stirring paddle, the stirring speed, and the viscosity of the material. If the stirring Reynolds number is too low, the washing effect will be poor, the residual lithium content will be high, and the material capacity will be low. When the stirring Reynolds number is too high, the residual lithium content will be low, and the phenomenon of primary particle release will be exacerbated, resulting in a decrease in material capacity. At the same time, the material structure will be destroyed, resulting in poor gas production performance.

[0014] In some embodiments, the stirring Reynolds number during the washing process is 3000 to 10000. Within this stirring Reynolds number range, the washing effect on the positive electrode material is better.

[0015] In some embodiments, the molar ratio of the lithium-containing material to the sodium-containing material is 3 to 5: 1. The presence of an appropriate amount of sodium during the washing process can effectively improve the gas production performance of the material. If the sodium content is too high, the capacity of the material will be reduced.

[0016] In some embodiments, the lithium-containing material is selected from at least one of lithium hydroxide, lithium carbonate, lithium acetate, or lithium chloride; and / or the sodium-containing material is selected from at least one of sodium hydroxide, sodium carbonate, sodium acetate, sodium chloride, or sodium aluminate.

[0017] In some embodiments, the solution U is an aqueous solution of the additive T.

[0018] In some embodiments, in step S1, the chemical formula of the ternary cathode material precursor is Ni x Co y Mn z (OH)2, where x≥0.9, y>0, z>0, x+y+z=1.

[0019] In some embodiments, the remixing process in step S1 comprises cooling the pre-fired material and then remixing it. During the pre-fired process, moisture (water of crystallization) in the lithium source is decomposed and removed by high-temperature decomposition. After cooling and remixing the pre-fired material, it is re-filled into a pot. During calcination, no large amounts of moisture are generated, resulting in a more compact material structure.

[0020] In some embodiments, in step S1, the pre-calcination temperature is 450-650° C. and the pre-calcination time is 5-20 hours. Under these pre-calcination conditions, the crystal water in the raw material can be relatively completely removed.

[0021] In some embodiments, in step S1, the calcination temperature is 700-850° C., and the calcination time is 5-20 hours.

[0022] In some embodiments, the chemical formula of the primary ternary cathode material is LiNi x Co y Mn z O2, where x≥0.9, y>0, z>0, x+y+z=1.

[0023] In some embodiments, in step S1, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium oxalate, lithium citrate, or lithium acetate.

[0024] In some embodiments, the molar ratio of the ternary cathode material precursor to the lithium element in the lithium source is 1:(1-1.15).

[0025] In some embodiments, in step S2, the molar concentration of solution U is 0.05 to 0.1 mol / L. The molar concentration refers to the total concentration of cations or anions contained in solution U. By controlling the cation concentration in the solution, the washing process not only prevents excessive removal of residual alkali on the surface of the material but also allows additives to be coated on the surface of the material, optimizing material storage and gas production performance, thereby ensuring a thorough washing effect.

[0026] In some embodiments, in step S2, the particle size Dv50 of the primary ternary cathode material is 8 to 10 μm. The particle size of the primary ternary cathode material affects the viscosity of the material during the washing process. The larger the particle size, the greater the viscosity of the material.

[0027] In some embodiments, in step S2, the solid-liquid ratio of the primary ternary cathode material to the solution U is 1-3 kg / L. The solid-liquid ratio of the primary ternary cathode material to the solution U affects the viscosity of the material during the washing process, and the washing effect of the material is better within this range.

[0028] In some embodiments, in step S2, the temperature of the solution U is 2-25° C. If the solution temperature is too high, it will have a negative impact on the gas production performance of the material.

[0029] In some embodiments, in step S2, the stirring speed of the washing is 20 to 2000 rpm. The stirring speed affects the stirring Reynolds number of the washing process. If the stirring speed is too low, the washing effect on the material is limited; if the stirring speed is too high, the residual alkali on the surface of the material is excessively washed away, the capacity is reduced, and the surface structure of the material is also damaged.

[0030] In some embodiments, in step S2, after the primary ternary cathode material is mixed and washed with the solution U, the primary ternary cathode material is further centrifuged at a speed of 20 to 80 Hz in a nitrogen atmosphere.

[0031] In some embodiments, in step S2, the drying temperature is 110-150° C., and the drying time is 3-8 hours.

[0032] In some embodiments, in step S2, the secondary ternary cathode material is further sieved, and the mesh size of the sieve is 200 meshes.

[0033] In some embodiments, in step S3, the atomic layer deposition process is as follows: ALD (atomic layer deposition) reagents are introduced into the secondary ternary cathode material under negative pressure, followed by the introduction of an inert gas, followed by the introduction of water vapor after evacuation, followed by the introduction of an inert gas again, and then the evacuation again, and the above steps are repeated 10 to 30 times to obtain the ternary cathode material. The ALD reagents undergo chemical adsorption on the material surface, and the subsequent introduction of water vapor reacts with the ALD reagents to form a coating layer on the material surface. The thickness of the coating layer is controlled by the deposition time and number of depositions.

[0034] In some embodiments, the coating layer of the ternary cathode material has a thickness of 1 to 10 nm. If the coating layer thickness is too low, the material may not be fully coated; if the coating layer is too thick, it may have a negative impact on the capacity of the material.

[0035] In some embodiments, the negative pressure is a pressure lower than 10 Pa.

[0036] In some embodiments, the ALD reagent is at least one of titanium tetrachloride, isopropyl titanate, silicon tetrachloride, trimethylaluminum, germanium tetrafluoride, tris(N,N'-diisopropylformamidinium)lanthanum, or tetrakis(dimethylamino)zirconium.

[0037] In some embodiments, the ALD reagent is trimethylaluminum. When improving the storage and gas production performance of the material, using trimethylaluminum as the ALD reagent has a better effect.

[0038] In some embodiments, the time for introducing the ALD reaction reagent is 2 to 5 seconds.

[0039] In some embodiments, the time for introducing the inert gas is about 120 seconds; the inert gas is argon.

[0040] In some embodiments, the time for introducing the water vapor is about 5 to 15 seconds.

[0041] In some embodiments, the temperature of the water vapor is 100-150°C.

[0042] In some embodiments, the temperature of the atomic layer deposition process is 100-150° C. The temperature of the atomic layer deposition reaction chamber within this range is conducive to the reaction between water vapor and ALD reaction reagents.

[0043] The washed high-nickel ternary material is used as the ALD substrate. Since the washing process has already generated a protective layer of spinel phase on the material surface, it can protect the substrate from being destroyed by water vapor during the ALD reaction, allowing the material to obtain a uniform metal oxide coating, reducing the material's specific surface area while maintaining its structure.

[0044] According to the second aspect of the present disclosure, a ternary positive electrode material is proposed, which is prepared by the preparation method described in the first aspect of the present disclosure. The sodium content of the ternary positive electrode material is 0.01% to 0.2%, the sulfur content is less than 0.1%, and the mass content of residual lithium is 0.15% to 0.3%. After the ternary positive electrode material is washed in a sodium-containing solution, a small amount of sodium element is coated on the surface, which can reduce the side reactions of the material with the electrolyte during storage, thereby helping to improve the storage capacity retention rate and gas production performance of the material. Since the precursor of the ternary material is prepared by co-precipitation of transition metal sulfates, if the residual sulfur content is too high, it will affect the capacity of the material. If the residual lithium content is too high, the side reactions of the material during the cycle are more serious. If the residual lithium content is too low, the lattice lithium of the material is easily washed out during the washing process, resulting in a decrease in capacity.

[0045] According to a third aspect of the present disclosure, a lithium-ion battery is provided, comprising the ternary cathode material as described in the second aspect of the present disclosure.

[0046] According to one embodiment of the present disclosure, there are at least the following beneficial effects:

[0047] (1) The present invention avoids loosening of the material after dehydration of the precursor and the lithium source by pre-sintering, re-mixing, and re-sintering the ternary material precursor, increases the contact area between the materials during the sintering process, makes the secondary balls of the material more tightly bonded, improves the hardness of the material, and improves the material's resistance to washing.

[0048] (2) The present disclosure controls the Reynolds number during the washing process and the flow of the fluid to achieve the purpose of controlling the degree of washing. By controlling the washing intensity within a certain range, the residual lithium can be reduced to an appropriate range, avoiding lithium deficiency or primary particle release due to excessive washing. At the same time, the present disclosure suppresses excessive washing of residual lithium on the surface of the material by adding lithium-containing materials and sodium-containing materials to the washing solution, and at the same time, a small amount of sodium element is coated on the surface of the material, thereby optimizing the storage and gas production performance of the material. The high-nickel ternary positive electrode material prepared by the method described in the present disclosure has a high capacity and is suitable for application in the field of lithium-ion batteries.

[0049] (3) The present invention performs atomic layer deposition coating on the washed ternary positive electrode material, coating the surface of the material with a nano-scale oxide coating layer to repair the damage caused by washing to the surface of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The present disclosure is further described below with reference to the accompanying drawings and embodiments, wherein:

[0051] FIG1 is a SEM image of the high-nickel ternary positive electrode material prepared in Example 1 of the present disclosure, magnified 10,000 times;

[0052] FIG2 is a SEM image of the high-nickel ternary positive electrode material prepared in Comparative Example 1 of the present disclosure, magnified 10,000 times;

[0053] FIG3 is a SEM image of the high-nickel ternary positive electrode material prepared in Comparative Example 2 of the present disclosure, magnified 10,000 times;

[0054] FIG4 is a graph showing gas production data of Examples 1-2 and Comparative Examples 2-3 at 70° C.

[0055] FIG5 is a storage data diagram of Examples 1-2 and Comparative Examples 2-3 of the present disclosure at 60° C. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the concept and technical effects of the present disclosure in conjunction with embodiments to fully understand the purpose, features and effects of the present disclosure.

[0057] Example 1

[0058] A method for preparing a ternary positive electrode material comprises the following steps:

[0059] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01(OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0060] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0061] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0062] (4) Take 4 L of deionized water at 10°C, add 67.11 g of lithium hydroxide monohydrate and 16.00 g of sodium hydroxide to prepare solution U.

[0063] (5) Take solution U and place it in a water washing kettle with a stirring blade diameter of 16 cm and stir it at 150 rpm for 10 minutes. Then add 10 kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2 was added to the reactor and stirred at a Reynolds number of 4000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0064] (6) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, wait until the pressure drops below 10 Pa, open the valve of the container containing trimethylaluminum, and introduce trimethylaluminum vapor into the reaction chamber and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. Wait until the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber and maintain it for 10 seconds. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating. The SEM image of the high-nickel ternary positive electrode material C is shown in Figure 1.

[0065] Example 2

[0066] A method for preparing a ternary positive electrode material comprises the following steps:

[0067] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0068] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0069] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0070] (4) Take 5 L of deionized water at 10°C, add 83.88 g of lithium hydroxide monohydrate and 20.00 g of sodium hydroxide to prepare solution U.

[0071] (5) Take solution U and place it in a water washing kettle with a stirring blade diameter of 16 cm and stir it at 150 rpm for 10 minutes. Then add 10 kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2 was added to the reactor and stirred at a Reynolds number of 10,000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0072] (6) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, and wait until the pressure drops below 10 Pa. Open the valve of the container containing trimethylaluminum, introduce trimethylaluminum vapor into the reaction chamber, and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon gas into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. When the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber, and maintain it for 10 seconds. Introduce argon gas into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating.

[0073] Comparative Example 1

[0074] A method for preparing a ternary positive electrode material, which differs from Example 1 only in that the sintering process of the mixture A is different, specifically comprising the following steps:

[0075] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0076] (2) Place the mixture A in a box furnace for sintering at a temperature curve of 530°C / 8h+710°C / 10h in an oxygen atmosphere to obtain the ternary cathode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0077] (3) Take 4 L of deionized water at 10°C, add 67.11 g of lithium hydroxide monohydrate and 16.00 g of sodium hydroxide to prepare solution D1.

[0078] (4) Take solution D1, place it in a water washing kettle with a stirring blade diameter of 16 cm and stir it at 150 rpm for 10 minutes, then add 10 kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2 was added to the reactor and stirred at a Reynolds number of 4000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0079] (5) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, and wait until the pressure drops below 10 Pa. Open the valve of the container containing trimethylaluminum, and introduce trimethylaluminum vapor into the reaction chamber and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. When the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber, and maintain it for 10 seconds. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating. The SEM image of the high-nickel ternary positive electrode material C is shown in Figure 2.

[0080] Comparative Example 2

[0081] A method for preparing a ternary positive electrode material, which differs from Example 1 only in that the parameters of the washing process are different, specifically comprises the following steps:

[0082] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0083] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0084] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0085] (4) Take 5 L of deionized water at 10°C, add 83.88 g of lithium hydroxide monohydrate and 20.00 g of sodium hydroxide to prepare solution D2.

[0086] (5) Take solution D2, place it in a water washing kettle with a stirring blade diameter of 16 cm and stir it at 400 rpm for 10 minutes, then add 10 kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2 was added to the reactor and stirred at a Reynolds number of 50,000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0087] (6) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, and wait until the pressure drops below 10 Pa. Open the valve of the container containing trimethylaluminum, and introduce trimethylaluminum vapor into the reaction chamber and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. When the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber, and maintain it for 10 seconds. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating. The SEM image of the high-nickel ternary positive electrode material C is shown in Figure 3.

[0088] Comparative Example 3

[0089] A method for preparing a ternary positive electrode material, which differs from Example 1 only in that the amount of lithium hydroxide monohydrate added in step (4) is different and no sodium hydroxide is added, specifically comprising the following steps:

[0090] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0091] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0092] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0093] (4) Take 4 L of deionized water at 10°C and add 83.88 g of lithium hydroxide monohydrate to prepare solution D3.

[0094] (5) Take solution D3, place it in a water washing kettle with a stirring blade diameter of 16 cm and stir it at 150 rpm for 10 minutes, then add 10 kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01O2 was added to the reactor and stirred at a Reynolds number of 4000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0095] (6) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, and wait until the pressure drops below 10 Pa. Open the valve of the container containing trimethylaluminum, introduce trimethylaluminum vapor into the reaction chamber, and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon gas into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. When the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber, and maintain it for 10 seconds. Introduce argon gas into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating.

[0096] Comparative Example 4

[0097] A method for preparing a ternary positive electrode material, which differs from Example 1 only in that the amount of sodium hydroxide added is different and lithium hydroxide monohydrate is not added, specifically comprising the following steps:

[0098] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0099] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0100] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0101] (4) Take 4 L of deionized water at 10°C and add 80.00 g of sodium hydroxide to prepare solution D4.

[0102] (5) Take solution D4, place it in a water washing kettle with a stirring blade diameter of 16 cm and stir it at 150 rpm for 10 minutes, then add 10 kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2 was added to the reactor and stirred at a Reynolds number of 4000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0103] (6) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, and wait until the pressure drops below 10 Pa. Open the valve of the container containing trimethylaluminum, introduce trimethylaluminum vapor into the reaction chamber, and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon gas into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. When the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber, and maintain it for 10 seconds. Introduce argon gas into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating.

[0104] Comparative Example 5

[0105] A method for preparing a ternary positive electrode material, which differs from Example 1 only in that lithium hydroxide monohydrate and sodium hydroxide are not added in step (4), specifically comprising the following steps:

[0106] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0107] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0108] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2.

[0109] (4) Take 4L of deionized water at 10℃ and place it in a water washing kettle with a stirring blade of 16cm in diameter and stir it at 150rpm for 10min. Then, add 10kg of ternary positive electrode material LiNi 0.92 Co 0.07 Mn 0.01 O2 was added to the reactor and stirred at a Reynolds number of 4000 for 2 minutes. The mixture was then placed in a centrifuge and centrifuged at 50 Hz for 50 minutes. The mixture was then dried in a vibration dryer at 150°C for 3 hours at a vibration frequency of 50 Hz. After drying, the mixture was sieved with a 200-mesh sieve to obtain high-nickel ternary cathode material B.

[0110] (5) Place the high-nickel ternary material B in the ALD reaction chamber, evacuate the reaction chamber, and wait until the pressure drops below 10 Pa. Open the valve of the container containing trimethylaluminum, and introduce trimethylaluminum vapor into the reaction chamber and maintain it for 3 seconds. The temperature of the reaction chamber is 120°C. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted trimethylaluminum. When the pressure in the reaction chamber drops to 10 Pa, open the valve of the container containing water, introduce water vapor into the reaction chamber, and maintain it for 10 seconds. Introduce argon into the reaction chamber for 120 seconds, then evacuate the chamber to remove unreacted water vapor. Repeat the above cycle 20 times to obtain a high-nickel ternary positive electrode material C with a nano-scale alumina coating.

[0111] Comparative Example 6

[0112] A method for preparing a ternary cathode material, which differs from Example 1 only in that washing and atomic layer deposition are not performed, specifically comprises the following steps:

[0113] (1) Take 11.100 kg of nickel cobalt manganese hydroxide precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and 5.059 kg of coarse-grained lithium hydroxide (Dv50 range of 200-350 μm) were placed in a high-speed mixer and mixed once. The mixing parameters were 150 rpm and 15 min to obtain mixture A.

[0114] (2) The mixture A was placed in a box furnace for pre-sintering at a temperature of 530°C for 8 hours in an oxygen atmosphere to obtain pre-sintered material A.

[0115] (3) Pour the pre-burned material A into a high-efficiency mixer and mix it at a speed of 300 rpm for 15 minutes. After the mixing is completed, place it in a box furnace for primary sintering at a sintering temperature of 710 ° C, a holding time of 10 hours, and an oxygen atmosphere to obtain a ternary positive electrode material LiNi 0.92 Co0.07 Mn 0.01 O2.

[0116] Test example

[0117] The examples and comparative examples of the present disclosure were tested for Na content, S content, residual lithium, charge and discharge capacity, and first-cycle coulomb efficiency. The Na and S contents were tested using the ICP method, and the element wavelengths used for analysis were: Na 589.592nm, S 180.669nm. The residual lithium content of LiOH and Li2CO3 was tested using a potentiometric titration method. The charge capacity, discharge capacity, and first-cycle efficiency were tested using a constant current charge and discharge method with a current density of 0.1C and a cut-off voltage of 2.8 to 4.3V. The test results are shown in Table 1:

[0118] Table 1

[0119] It can be seen that in Comparative Example 1, there is no pre-calcination process, and the residual lithium after washing is lower than that in Example 1 under the same experimental conditions, and the capacity is low; in Comparative Example 2, the stirring speed is increased, the washing degree is increased, and the lithium carbonate and LiOH are significantly decreased compared with the embodiment, and the capacity is low; in Comparative Example 3, only lithium hydroxide is used for washing while maintaining the same hydroxide concentration, and the washing liquid lacks sodium ions, resulting in poor gas production and storage performance; in Comparative Example 4, only sodium hydroxide is used for washing while maintaining the same hydroxide concentration, and the washing liquid lacks lithium ions, resulting in more obvious lithium release from the surface of the material, significantly lower residual lithium than the embodiment, and decreased capacity; in Comparative Example 5, pure water is used for washing, which makes it easier for alkaline substances and lithium on the surface of the material to be washed away, seriously damaging the surface structure of the material, resulting in a significant decrease in residual lithium and capacity; in Comparative Example 6, the washing step is removed, and the obtained finished product LiOH and residual lithium content are high, and the capacity is low.

[0120] The high-nickel positive electrode materials prepared in the embodiments and comparative examples of the present disclosure were subjected to SEM tests, and the test results are shown in Figures 1 to 3. As can be seen from Figure 1, the positive electrode material particles prepared in Example 1 have no cracking, and there is no primary particle detachment phenomenon; as can be seen from Figure 2, the high-nickel positive electrode material prepared in Comparative Example 1 shows small particle disintegration at a high stirring speed, and obvious primary particle detachment phenomenon, which may be due to the lack of a pre-burning process, resulting in a weak binding force of the secondary balls themselves, which are easy to disintegrate during the washing process. As can be seen from Figure 3, the high-nickel positive electrode material after pre-burning can still maintain structural integrity under a washing process with a higher Reynolds number, and only a small amount of primary particles detach. This shows that the sample using the pre-burning process can indeed enhance the structural stability of the secondary balls.

[0121] The embodiments and comparative examples of the present disclosure were subjected to a soft-pack gas production test at 70°C, and the test results are shown in Figure 4. It can be seen from the experimental results that the gas production result of Example 1 is the best, followed by Example 2, which shows that the use of lithium hydroxide and sodium hydroxide solution for washing can reduce the gas production of the material. In addition, controlling the Reynolds number at a lower level can further reduce the gas production. The gas production of Comparative Example 2 was significantly higher than that of other samples after 20 days, indicating that although only a small amount of primary particles escaped, the gas production was still significantly increased, proving that a washing process with a higher Reynolds number will destroy the material structure and cause the material to produce too much gas during high-temperature storage. From the gas production of Comparative Example 3, it can be seen that not adding sodium hydroxide to the washing solution will cause the gas production performance of the material to deteriorate. It may be that the presence of sodium hydroxide in the washing solution will cause the surface of the material to be coated with sodium elements. The presence of sodium elements may reduce the side reactions produced by the material and the electrolyte in a high-temperature environment, thereby reducing the gas production.

[0122] The embodiments and comparative examples of the present disclosure were subjected to a soft pack storage test at 60°C, and the test results are shown in Figure 5. Similar to the gas production results, the storage performance of the embodiments is significantly better, indicating that the use of a lithium hydroxide and sodium hydroxide mixed solution and a washing process that controls the Reynolds number are beneficial to the storage performance of the material. The storage performance of comparative example 2 is significantly poor, which may be due to the partial escape of small particles, resulting in more pores on the surface of the material and faster capacity decay during storage. Comparative example 3 shows that the lack of sodium ions on the surface of the material will deteriorate the storage performance, indicating that the presence of sodium ions is helpful to the storage performance of the material.

Claims

1. A preparation method of a ternary cathode material with a coating layer, characterized in that It includes the following steps: S1: Mix the ternary material precursor with a lithium source and perform pre-calcination to obtain a pre-calcined material. After remixing the pre-calcined material, perform calcination to obtain a primary ternary cathode material; S2: Dissolve additive T to obtain solution U. Mix and wash the primary ternary cathode material with solution U, and perform drying to obtain a secondary ternary cathode material; S3: Perform atomic layer deposition treatment on the secondary ternary cathode material to obtain a ternary cathode material; The additive T is composed of a lithium-containing material and a sodium-containing material; During the washing process, the stirring Reynolds number is 200 - 20000.

2. The preparation method according to claim 1, characterized in that, During the washing process, the stirring Reynolds number is 3000 - 10000.

3. The preparation method according to claim 1, characterized in that The molar ratio of the lithium-containing material to the sodium-containing material is 3 - 5:

1.

4. The preparation method according to claim 1, characterized in that, In step S1, the chemical formula of the ternary cathode material precursor is Ni x Co y Mn z (OH)2, where x ≥ 0.9, y > 0, z > 0, and x + y + z = 1.

5. The preparation method according to claim 1, wherein In step S1, the process of remixing is: after cooling the pre-calcined material, perform remixing treatment again.

6. The preparation method according to claim 1, characterized in that, In step S2, the molar concentration of solution U is 0.05 - 0.1 mol / L.

7. The preparation method according to claim 1, characterized in that, In step S2, the particle size Dv50 of the primary ternary cathode material is 8 - 10 μm.

8. The preparation method according to claim 1, wherein In step S2, the solid-liquid ratio of the primary ternary cathode material to solution U is 1 - 3 kg / L.

9. The preparation method according to claim 1, characterized in that, In step S2, the temperature of solution U is 2 - 25 °C.

10. The preparation method according to claim 1, wherein, In step S2, the stirring speed during washing is 20 - 2000 rpm.

11. The preparation method according to claim 1, characterized in that, In step S3, the process of atomic layer deposition treatment is: under negative pressure, introduce an ALD reaction reagent into the secondary ternary cathode material, then introduce an inert gas, evacuate, introduce water vapor, introduce an inert gas again, re-evacuate, and repeat the above steps 10 - 30 times to obtain the ternary cathode material.

12. The preparation method according to claim 11, wherein, The ALD reaction reagent is at least one of titanium tetrachloride, isopropyl titanate, silicon tetrachloride, trimethylaluminum, germanium tetrafluoride, lanthanum tris(N,N'-diisopropylformamidine), or zirconium tetrakis(dimethylamino).

13. The preparation method according to claim 11, characterized in that, The time for introducing the ALD reaction reagent is 2 - 5 s.

14. The preparation method according to claim 11, wherein, The time for introducing the water vapor is 5 - 15 s.

15. The preparation method according to claim 11, characterized in that, The temperature of the atomic layer deposition treatment is 100 - 150 °C.

16. A ternary cathode material prepared by the preparation method according to any one of claims 1-15, characterized in that, The sodium content of the ternary cathode material is 0.01% - 0.2%, the sulfur content < 0.1%, and the mass content of residual lithium is 0.15% - 0.3%.

17. A lithium-ion battery, characterized in that, It includes the ternary cathode material as described in claim 16.

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