High-nickel ternary positive electrode material coated with an outer coating layer and a preparation method thereof

Abstract

The present disclosure relates to an outer coating coated high-nickel ternary positive electrode material and a preparation method thereof, and belongs to the technical field of lithium ion battery positive electrode materials. In the preparation method of the outer coating coated high-nickel ternary positive electrode material, silane coupling agent solution and lithium polyacrylate solution are respectively sprayed on the surface of the high-nickel ternary positive electrode material to form an outer coating and coat the surface of the high-nickel ternary positive electrode material, which can significantly reduce the sensitivity of the high-nickel ternary positive electrode material to air moisture, improve its storage performance in air and electrochemical performance. The outer coating includes hydrophobic coating lithium organosilicate and lithium polyacrylate. By adding the silane coupling agent, the residual alkali on the surface of the high-nickel ternary positive electrode material can be reacted to obtain lithium organosilicate with lipophilic hydrophobic functional groups, which is combined with lithium polyacrylate on the surface of the high-nickel ternary positive electrode material, significantly reducing the residual alkali on the surface of the high-nickel ternary positive electrode material and inhibiting the substantial conversion of LiOH to Li2CO3.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery cathode material technology, and in particular to a high-nickel ternary cathode material with an outer coating and its preparation method. Background Technology

[0002] High-nickel layered oxide materials are considered ideal cathode materials for high-energy-density lithium-ion batteries due to their high reversible capacity. However, these materials, especially those with high specific surface area, porous structure, and strong chemical hydrophilicity, absorb water when exposed to the atmosphere, leading to the formation of residual lithium compounds on the material surface and the problem of residual lithium. Furthermore, this damage will further absorb more moisture during subsequent storage, thus severely corroding the cathode oxide.

[0003] Residual lithium compounds are inevitably present in high-nickel ternary cathode materials. They are usually detected as a mixture of Li₂O, LiOH, and Li₂CO₃, and their proportion varies with storage conditions such as humidity and time. Their quantity increases with the nickel content in the high-nickel ternary cathode material. During the synthesis of most high-nickel ternary cathode materials, a small amount of lithium salt inevitably remains on the surface. When exposed to air, this reacts with H₂O and CO₂, gradually transforming into LiOH and Li₂CO₃. The residual lithium problem on the surface of high-nickel ternary cathode materials leads to numerous problems such as capacity decay, low lithium-ion diffusion performance, and poor cycle performance. For example, excessively high residual alkali content on the surface of high-nickel ternary cathode materials can cause slurry gelation during cathode slurry preparation, severely affecting the battery coating process; it can also react with LiPF₆ in the electrolyte to generate HF and CO₂, causing battery gas and posing a significant safety hazard. A common method for removing residual alkali is water washing. However, water washing not only increases costs but also makes it difficult to control the operation. After water washing, the structure of high-nickel ternary cathode materials deteriorates, and their performance is severely degraded, resulting in a reduced washing effect. Therefore, reducing the residual alkali content on the surface of high-nickel ternary cathode materials and improving their surface moisture resistance are key to solving the processing performance and safety performance issues of high-nickel ternary cathode materials.

[0004] Currently, the technical means used to effectively improve the moisture sensitivity of high-nickel ternary cathode materials include doping, coating, and other surface modification methods. For example, in the coating scheme, CN105336927A discloses a modified superhydrophobic material, which is coated on the surface of high-nickel cathode material particles in a three-dimensional network form and filled between particles. This can effectively achieve hydrophobic and conductive treatment of the surface of high-nickel cathode material, reduce sensitivity to environmental moisture, reduce side reactions between trace water and electrolyte, and improve the safety, cycle life, and storage performance of high-nickel cathode material in lithium-ion batteries. However, since the particles of high-nickel cathode material in this scheme are only bridged by the modified superhydrophobic material rather than forming strong chemical bonds, it is difficult to ensure that the hydrophobic material will not fall off during subsequent battery manufacturing processes, thus limiting the hydrophobicity between these active materials. Summary of the Invention

[0005] Based on this, the purpose of this disclosure is to provide a method for preparing a high-nickel ternary cathode material with an outer coating. By adding lithium polyacrylate and a silane coupling agent to the surface of the high-nickel ternary cathode material, the residual alkali content on the surface of the high-nickel ternary cathode material can be effectively reduced. Simultaneously, the added lithium polyacrylate has a binding effect, which can strengthen the bonding between the outer coating and the surface of the high-nickel ternary cathode material, allowing the surface of the high-nickel ternary cathode material to exhibit a stable outer coating structure with oleophilic and hydrophobic functional groups. This significantly improves the storage performance, safety, and processing performance of the high-nickel ternary cathode material for lithium-ion batteries, thus facilitating its industrial application. The method for preparing the high-nickel ternary cathode material with an outer coating described in this disclosure effectively solves the problems of residual alkali on the surface of high-nickel ternary cathode materials and their sensitivity to air.

[0006] A method for preparing a high-nickel ternary cathode material with an outer coating includes the following steps:

[0007] Preparation of silane coupling agent solution;

[0008] Preparation of lithium polyacrylate solution;

[0009] The high-nickel ternary cathode material is dried and then placed in a mixer for premixing. After premixing, the silane coupling agent solution and the lithium polyacrylate solution are simultaneously sprayed onto the high-nickel ternary cathode material in the mixer through different nozzles while being sprayed and stirred. After the process is completed, a drying heat treatment is performed to obtain a high-nickel ternary cathode material with an outer coating.

[0010] In one embodiment, the silane coupling agent is prepared by dissolving the silane coupling agent in a first solvent to obtain the silane coupling agent solution.

[0011] In one embodiment, the chemical formula of the silane coupling agent is YSiX3, where Y is a hydrophobic functional group, which is one of a hydrocarbon group, an ester group, a phenyl group, or a fluorophenyl group; and X is a hydrolyzable group, which is one of a methoxy group, a halogen group, an ethoxy group, or an acetoxy group. In another embodiment, Y can also be a hydrocarbon group containing fluorine / double bond / aryl / ester / ether / amine / amide groups.

[0012] In one embodiment, Y is one of methyl, propyl, phenyl, butyl, octyl, or vinyl.

[0013] In one embodiment, the amount of the silane coupling agent is 0.5% to 5% of the mass of the high-nickel ternary cathode material.

[0014] In one embodiment, the first solvent is a volatile organic solvent, namely one or more of anhydrous ethanol, anhydrous methanol, and acetone.

[0015] In one embodiment, the lithium polyacrylate solution is prepared by dissolving polyacrylic acid and lithium hydroxide in a second solvent to obtain a lithium polyacrylate solution, wherein the pH of the lithium polyacrylate solution is 5-9.

[0016] In one embodiment, the amount of polyacrylic acid used is 0.5% to 3% of the mass of the high-nickel ternary cathode material, and the molecular weight of the polyacrylic acid is 250,000 to 500,000.

[0017] In one embodiment, the second solvent is one or more of water, anhydrous ethanol, and isopropanol.

[0018] In one embodiment, the volume concentration of the silane coupling agent solution is 10–100%; the volume concentration of the lithium polyacrylate solution is 10–100%.

[0019] In one embodiment, the dissolution method during the preparation of the silane coupling agent solution and the lithium polyacrylate solution is selected from one of stirring dissolution, oscillation dissolution, ultrasonic dissolution, and microwave-assisted dissolution, and the temperature is room temperature.

[0020] In one embodiment, the chemical formula of the high-nickel ternary cathode material is LiNixCoyMzO2, where M is element Mn or element Al; x takes values ​​of 0.7 to 1.0, y takes values ​​of 0 to 0.3, z takes values ​​of 0 to 0.3, and x + y + z = 1.

[0021] In one embodiment, the high-nickel ternary cathode material is dried in a vacuum oven at a temperature of 90°C to 180°C for 0.5 to 3 hours.

[0022] In one embodiment, the silane coupling agent solution and the lithium polyacrylate solution are first loaded into different spray equipment containers. Then, after the high-nickel ternary cathode material is premixed, the silane coupling agent solution and the lithium polyacrylate solution are simultaneously sprayed onto the high-nickel ternary cathode material in the mixer at different nozzles.

[0023] In one embodiment, in step (3), the speed of the mixer is 300 to 1200 rpm, and the premixing time is 1 to 10 minutes.

[0024] In one embodiment, in step (3), the spraying conditions for the silane coupling agent solution and the lithium polyacrylate solution on the spraying equipment are both: a spraying speed of 5-50 ml / min and a spraying time of 2-15 minutes.

[0025] In one scheme, step (3) involves stirring for 1 to 10 minutes.

[0026] In one embodiment, in step (3), the drying heat treatment conditions are oven drying at a temperature of 90–150°C for 2–24 hours.

[0027] This disclosure also provides a high-nickel ternary cathode material with an outer coating, which is obtained by any of the above-described methods for preparing a high-nickel ternary cathode material with an outer coating.

[0028] This disclosure has the following beneficial effects:

[0029] 1. In the preparation method of the high-nickel ternary cathode material with an external coating disclosed herein, an external coating is formed by spraying the silane coupling agent solution and the lithium polyacrylate solution onto the surface of the high-nickel ternary cathode material, respectively. This coating significantly reduces the sensitivity of the high-nickel ternary cathode material to air moisture and improves its storage performance and electrochemical performance in air. The external coating comprises lithium organosilicon and lithium polyacrylate. By adding the silane coupling agent, it can react with the residual alkali on the surface of the high-nickel ternary cathode material to obtain lithium organosilicon with oleophilic and hydrophobic functional groups. Furthermore, the silane coupling agent can form Si-O chemical bonds with the surface of the high-nickel ternary cathode material, creating strong chemical bonds that prevent detachment. This disclosure further utilizes lithium polyacrylate, which has a certain degree of adhesion, to enhance the bonding with the material surface. By adding the lithium polyacrylate, on the one hand, the bonding between the hydrophobic functional group of organosilicon lithium and the surface of the high-nickel ternary cathode material is more stable; on the other hand, lithium polyacrylate can also act as an ion conductor, additionally compensating for the lithium ion loss of the high-nickel ternary cathode material, and reducing the impact of the inactive substance, the silane coupling agent, on the electrochemical performance of the high-nickel ternary cathode material. This disclosure, through the synergistic bonding of the lithium polyacrylate and the silane coupling agent with the surface of the high-nickel ternary cathode material, can significantly reduce the residual alkali on the surface of the high-nickel ternary cathode material and inhibit the large-scale conversion of LiOH to Li2CO3. The residual alkali is rationally utilized to convert into a highly efficient outer coating on the surface of the high-nickel ternary cathode material, effectively improving the material's processing performance and safety performance.

[0030] 2. The present disclosure discloses an outer coating on the surface of a high-nickel ternary cathode material, comprising two effective substances present simultaneously. The organosilicon lithium generated on the surface of the high-nickel ternary cathode material provides a hydrophobic effect, while the polyacrylate lithium on the surface of the high-nickel ternary cathode material provides a binding and ion conductor effect. These two effective substances present on the surface of the high-nickel ternary cathode material together constitute the outer coating morphology.

[0031] 3. Compared to high-nickel ternary cathode materials without external coating, the high-nickel ternary cathode material with external coating prepared in this disclosure can significantly reduce surface moisture and residual Li in high-nickel ternary cathode materials. + This significantly improves the first-cycle capacity retention of high-nickel ternary cathode materials. The residual Li is reduced by reacting the silane coupling agent with the residual alkali on the surface of the high-nickel ternary cathode material. + quantity.

[0032] 4. Compared with the single-coating scheme in related technologies, the high-nickel ternary cathode material with external coating disclosed in this invention has a significant effect on reducing residual alkali. It does not affect the first-cycle capacity of the material, nor does it change the internal structure of the high-nickel ternary cathode material. The synthesized lithium polyacrylate is a conductive binder that can be used as an additional lithium salt to compensate for lost lithium ions. It can reduce the impact of the hydrophobic coating on the electrochemical performance of the high-nickel ternary cathode material, and can also effectively improve the adhesion between the hydrophobic coating and the material surface, prevent the active material from falling off during the subsequent coating process, and stably form a dense protective layer to isolate air and moisture, thus significantly improving the material's air sensitivity.

[0033] 5. The solvent used in the preparation method of the high-nickel ternary cathode material with external coating of the present disclosure is less toxic, and compared with the water washing scheme of related technologies, the preparation method of the high-nickel ternary cathode material with external coating of the present disclosure eliminates the water washing step, reducing costs. The preparation method of the high-nickel ternary cathode material with external coating of the present disclosure is simple, easy to operate and has obvious effects, with little environmental impact and considerable industrial application value.

[0034] 6. The amount of the silane coupling agent is 0.5% to 5% of the mass of the high-nickel ternary cathode material. If the amount of the silane coupling agent is too low, the content of the synthesized hydrophobic lithium organosilicon in the outer coating will be too low, resulting in poor surface hydrophobicity of the high-nickel ternary cathode material coated with the outer coating. If the amount of the silane coupling agent is too high, since the siloxane coupling agent is a non-active and non-conductive substance, it will adversely affect the electrochemical performance of the high-nickel ternary cathode material coated with the outer coating.

[0035] 7. The amount of polyacrylic acid used is 0.5% to 3% of the mass of the high-nickel ternary cathode material. If the amount of polyacrylic acid is too high, it will mask the hydrophobicity of the material and affect the electrochemical performance; if the amount of polyacrylic acid is too low, it will reduce the bonding effect and the lithium loss compensation effect, which will also affect the electrochemical performance.

[0036] To better understand and implement this disclosure, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0037] Figure 1 The graph shows the cycling data of the high-nickel ternary cathode materials in Examples 1-3 and Comparative Example 1;

[0038] Figure 2 The changes in the specific capacity of the high-nickel ternary cathode materials of Example 3 and Comparative Example 1 during the first discharge cycle of each day in an air exposure experiment;

[0039] Figure 3 This is a simplified diagram showing the combined use of a mixer and a spraying device. Detailed Implementation

[0040] Example 1

[0041] This embodiment provides a method for preparing a high-nickel ternary cathode material with an external coating, including the following steps:

[0042] (1) Measure 15 mL of methyltrimethoxysilane coupling agent and dissolve it in 35 mL of anhydrous ethanol to form a silane coupling agent solution, which is denoted as solution A.

[0043] (2) Take 24 mL of 30% polyacrylic acid solution and dilute it with deionized water to a 20% polyacrylic acid solution. Then add lithium hydroxide to the 20% polyacrylic acid solution. After the lithium hydroxide is completely dissolved, test the pH of the solution to be 7. The resulting lithium polyacrylic acid solution is denoted as solution B.

[0044] Place solutions A and B under an ultrasonic machine for 5 minutes to ensure that solutions A and B are thoroughly mixed.

[0045] (3) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02 O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, the prepared solutions A and B are loaded into different spray equipment containers, and the spray equipment is connected to the mixer. After premixing, solutions A and B, which have been loaded into the spray equipment containers, are simultaneously sprayed from different nozzles onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 10mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that solutions A and B are mixed evenly and in full contact with the high-nickel ternary cathode material. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material with an outer coating, which has hydrophobic properties.

[0046] Please see Figure 3 This is a simplified diagram of the mixing machine and spraying equipment used in the experiment. In the diagram, markings 1 and 3 refer to the air inlet pipe of the spraying equipment, markings 2 and 4 refer to the liquid inlet pipe of the spraying equipment, marking 5 refers to the degassing port of the mixing machine, and marking 6 refers to the mixing paddle of the mixing machine.

[0047] The high-nickel ternary cathode material with the outer coating obtained in this embodiment was subjected to storage testing experiments: air exposure experiments were conducted in a normal atmospheric environment, and a portion of the sample was taken daily to test the water content, residual lithium content, and first-cycle capacity. The test results showed that the smaller the increase in water content and residual lithium content, the better the moisture resistance of the coated high-nickel ternary cathode material. The higher the first-cycle capacity retention rate, the more it proved that the moisture resistance made the electrochemical performance of the high-nickel ternary cathode material more stable.

[0048] The results are as follows: The high-nickel ternary cathode material with an outer coating obtained in Example 1, before being exposed to air, had a water content of 0.0195%, a LiOH content of 0.3094%, and a Li2CO3 content of 0.1321%. Its first-cycle charge specific capacity was 244.6 mAh / g, its discharge specific capacity was 228.3 mAh / g, and its initial efficiency was 93.4%. After being exposed to air for 7 days, the water content was 0.4012%, the LiOH content was 0.44232%, and the Li2CO3 content was 0.5678%. Its first-cycle charge specific capacity was 244.0 mAh / g, its discharge specific capacity was 227.8 mAh / g, and its initial efficiency was 93.4%.

[0049] Example 2

[0050] This embodiment provides a method for preparing a high-nickel ternary cathode material with an external coating, including the following steps:

[0051] (1) Measure 30 mL of methyltrimethoxysilane coupling agent and dissolve it in 30 mL of anhydrous ethanol to form a silane coupling agent solution, which is denoted as solution A.

[0052] (2) Take 24 mL of 30% polyacrylic acid solution and dilute it with deionized water to a 20% polyacrylic acid solution. Then add lithium hydroxide to the 20% polyacrylic acid solution. After the lithium hydroxide is completely dissolved, test the pH of the solution to be 7. The resulting lithium polyacrylic acid solution is denoted as solution B.

[0053] Place solutions A and B under an ultrasonic machine for 5 minutes to ensure that solutions A and B are thoroughly mixed.

[0054] (3) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, the prepared solutions A and B are loaded into different spray equipment containers, and the spray equipment is connected to the mixer. After premixing, solutions A and B, which have been loaded into the spray equipment containers, are simultaneously sprayed from different nozzles onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 12mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that solutions A and B are mixed evenly and in full contact with the high-nickel ternary cathode material. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material with an outer coating, which has hydrophobic properties.

[0055] Please see Figure 3 In this embodiment, the mixing machine and spraying equipment used in the experiment are the same as in embodiment 1.

[0056] The high-nickel ternary cathode material with the outer coating obtained in this embodiment was subjected to storage testing experiments: air exposure experiments were conducted in a normal atmospheric environment, and a portion of the sample was taken daily to test the water content, residual lithium content, and first-cycle capacity. The test results showed that the smaller the increase in water content and residual lithium content, the better the moisture resistance of the coated high-nickel ternary cathode material. The higher the first-cycle capacity retention rate, the more it proved that the moisture resistance made the electrochemical performance of the high-nickel ternary cathode material more stable.

[0057] The results are as follows: The high-nickel ternary cathode material with an outer coating obtained in Example 2, before being exposed to air, had a water content of 0.0178%, a LiOH content of 0.2430%, and a Li2CO3 content of 0.1046%. Its first-cycle charge specific capacity was 244.6 mAh / g, its discharge specific capacity was 227.3 mAh / g, and its initial efficiency was 92.9%. After being exposed to air for 7 days, the water content was 0.3345%, the LiOH content was 0.4161%, and the Li2CO3 content was 0.5018%. Its first-cycle charge specific capacity was 248.7 mAh / g, its discharge specific capacity was 227.3 mAh / g, and its initial efficiency was 91.4%.

[0058] Example 3

[0059] This embodiment provides a method for preparing a high-nickel ternary cathode material with an external coating, including the following steps:

[0060] (1) Take 60 mL of methyltrimethoxysilane coupling agent and dissolve it in 30 mL of anhydrous ethanol to form a silane coupling agent solution, which is denoted as solution A.

[0061] (2) Take 71 mL of 30% polyacrylic acid solution and dilute it with deionized water to 20% polyacrylic acid solution. Then add lithium hydroxide to the 20% polyacrylic acid solution. After the lithium hydroxide is completely dissolved, test the pH of the solution to be 5. The resulting lithium polyacrylic acid solution is denoted as solution B.

[0062] Place solutions A and B under an ultrasonic machine for 5 minutes to ensure that solutions A and B are thoroughly mixed.

[0063] (3) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02 O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, the prepared solutions A and B are loaded into different spray equipment containers, and the spray equipment is connected to the mixer. After premixing, solutions A and B, which have been loaded into the spray equipment containers, are simultaneously sprayed from different nozzles onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 18mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that solutions A and B are mixed evenly and in full contact with the high-nickel ternary cathode material. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material with an outer coating, which has hydrophobic properties.

[0064] Please see Figure 3 In this embodiment, the mixing machine and spraying equipment used in the experiment are the same as in embodiment 1.

[0065] The hydrophobic high-nickel ternary cathode material with an outer coating obtained in this embodiment was subjected to storage testing experiments: air exposure experiments were conducted in a normal atmospheric environment, and a portion of the sample was taken daily to test the water content, residual lithium content, and first-cycle capacity. The smaller the increase in water content and residual lithium content, the better the moisture resistance of the coated high-nickel ternary cathode material. The higher the first-cycle capacity retention rate, the more it proves that the moisture resistance makes the electrochemical performance of the high-nickel ternary cathode material more stable.

[0066] The test results are as follows: Before being exposed to air, the high-nickel ternary cathode material with the outer coating obtained in Example 3 had a water content of 0.0154%, a LiOH content of 0.2058%, and a Li2CO3 content of 0.0963%. Its first-cycle charge specific capacity was 244.5 mAh / g, its discharge specific capacity was 228.9 mAh / g, and its initial efficiency was 93.6%. After being exposed to air for 7 days, the water content was 0.2896%, the LiOH content was 0.3871%, and the Li2CO3 content was 0.4526%. Its first-cycle charge specific capacity was 242.3 mAh / g, its discharge specific capacity was 226.9 mAh / g, and its initial efficiency was 93.6%.

[0067] Example 4

[0068] This embodiment provides a method for preparing a high-nickel ternary cathode material with an external coating, including the following steps:

[0069] (1) Take 90 mL of methyltrimethoxysilane coupling agent and denote it as solution A;

[0070] (2) Take 24 mL of 30% polyacrylic acid solution and dilute it with deionized water to a 20% polyacrylic acid solution. Then add lithium hydroxide to the 20% polyacrylic acid solution. After the lithium hydroxide is completely dissolved, test the pH of the solution to be 7. The resulting lithium polyacrylic acid solution is denoted as solution B.

[0071] Place solutions A and B under an ultrasonic machine for 5 minutes to ensure that solutions A and B are thoroughly mixed.

[0072] (3) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02 O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, the prepared solutions A and B are loaded into different spray equipment containers, and the spray equipment is connected to the mixer. After premixing, solutions A and B, which have been loaded into the spray equipment containers, are simultaneously sprayed from different nozzles onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 18mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that solutions A and B are mixed evenly and in full contact with the high-nickel ternary cathode material. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material with an outer coating, which has hydrophobic properties.

[0073] Please see Figure 3In this embodiment, the mixing machine and spraying equipment used in the experiment are the same as in embodiment 1.

[0074] The high-nickel ternary cathode material with the outer coating obtained in this embodiment was subjected to storage testing experiments: air exposure experiments were conducted in a normal atmospheric environment, and a portion of the sample was taken daily to test the water content, residual lithium content, and first-cycle capacity. The test results showed that the smaller the increase in water content and residual lithium content, the better the moisture resistance of the coated high-nickel ternary cathode material. The higher the first-cycle capacity retention rate, the more it proved that the moisture resistance made the electrochemical performance of the high-nickel ternary cathode material more stable.

[0075] The results are as follows: The high-nickel ternary cathode material with an outer coating obtained in Example 4, before being exposed to air, had a water content of 0.0126%, a LiOH content of 0.2728%, and a Li2CO3 content of 0.1196%. Its first-cycle charge specific capacity was 244.2 mAh / g, its discharge specific capacity was 226.1 mAh / g, and its initial efficiency was 92.6%. After being exposed to air for 7 days, the water content was 0.2298%, the LiOH content was 0.3631%, and the Li2CO3 content was 0.4028%. Its first-cycle charge specific capacity was 242.5 mAh / g, its discharge specific capacity was 224.2 mAh / g, and its initial efficiency was 92.5%.

[0076] Example 5

[0077] This embodiment provides a method for preparing a high-nickel ternary cathode material with an external coating, including the following steps:

[0078] (1) Measure 30 mL of propyltrimethoxysilane coupling agent and dissolve it in 30 mL of anhydrous ethanol to form a silane coupling agent solution, denoted as solution A;

[0079] (2) Take 24 mL of 30% polyacrylic acid solution and dilute it with deionized water to a 20% polyacrylic acid solution. Then add lithium hydroxide to the 20% polyacrylic acid solution. After the lithium hydroxide is completely dissolved, test the pH of the solution to be 7. The resulting lithium polyacrylic acid solution is denoted as solution B.

[0080] Place solutions A and B under an ultrasonic machine for 5 minutes to ensure that solutions A and B are thoroughly mixed.

[0081] (3) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, the prepared solutions A and B are loaded into different spray equipment containers, and the spray equipment is connected to the mixer. After premixing, solutions A and B, which have been loaded into the spray equipment containers, are simultaneously sprayed from different nozzles onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 12mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that solutions A and B are mixed evenly and in full contact with the high-nickel ternary cathode material. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material with an outer coating, which has hydrophobic properties.

[0082] Please see Figure 3 In this embodiment, the mixing machine and spraying equipment used in the experiment are the same as in embodiment 1.

[0083] The high-nickel ternary cathode material with the outer coating obtained in this embodiment was subjected to storage testing experiments: air exposure experiments were conducted in a normal atmospheric environment, and a portion of the sample was taken daily to test the water content, residual lithium content, and first-cycle capacity. The test results showed that the smaller the increase in water content and residual lithium content, the better the moisture resistance of the coated high-nickel ternary cathode material. The higher the first-cycle capacity retention rate, the more it proved that the moisture resistance made the electrochemical performance of the high-nickel ternary cathode material more stable.

[0084] The results are as follows: The high-nickel ternary cathode material with an outer coating obtained in Example 5, before being exposed to air, had a water content of 0.0165%, a LiOH content of 0.2458%, and a Li2CO3 content of 0.1478%. Its first-cycle charge specific capacity was 244.4 mAh / g, its discharge specific capacity was 227.0 mAh / g, and its initial efficiency was 92.9%. After being exposed to air for 7 days, the water content was 0.2934%, the LiOH content was 0.3945%, and the Li2CO3 content was 0.4793%. Its first-cycle charge specific capacity was 243.9 mAh / g, its discharge specific capacity was 226.4 mAh / g, and its initial efficiency was 92.8%.

[0085] Example 6

[0086] This embodiment provides a method for preparing a high-nickel ternary cathode material with an external coating, including the following steps:

[0087] (1) Take 30 mL of phenyltrimethoxysilane coupling agent and dissolve it in 30 mL of anhydrous ethanol to form a solution, which is denoted as solution A;

[0088] (2) Take 471 mL of 30% polyacrylic acid solution and dilute it with deionized water to 20% polyacrylic acid solution. Then add lithium hydroxide to the 20% polyacrylic acid solution. After the lithium hydroxide is completely dissolved, test the pH of the solution to be 5. The resulting lithium polyacrylic acid solution is denoted as solution B.

[0089] Place solutions A and B under an ultrasonic machine for 5 minutes to ensure that solutions A and B are thoroughly mixed.

[0090] (3) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02 O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, the prepared solutions A and B are loaded into different spray equipment containers, and the spray equipment is connected to the mixer. After premixing, solutions A and B, which have been loaded into the spray equipment containers, are simultaneously sprayed from different nozzles onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 12mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that solutions A and B are mixed evenly and in full contact with the high-nickel ternary cathode material. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material with an outer coating, which has hydrophobic properties.

[0091] Please see Figure 3 In this embodiment, the mixing machine and spraying equipment used in the experiment are the same as in embodiment 1.

[0092] The high-nickel ternary cathode material with the outer coating obtained in this embodiment was subjected to storage testing experiments: air exposure experiments were conducted in a normal atmospheric environment, and a portion of the sample was taken daily to test the water content, residual lithium content, and first-cycle capacity. The test results showed that the smaller the increase in water content and residual lithium content, the better the moisture resistance of the coated high-nickel ternary cathode material. The higher the first-cycle capacity retention rate, the more it proved that the moisture resistance made the electrochemical performance of the high-nickel ternary cathode material more stable.

[0093] The results are as follows: The high-nickel ternary cathode material with hydrophobic coating obtained in Example 6, before being exposed to air, had a water content of 0.0187%, a LiOH content of 0.2379%, and a Li2CO3 content of 0.1102%. Its first-cycle charge specific capacity was 245.3 mAh / g, its discharge specific capacity was 228.4 mAh / g, and its initial efficiency was 93.1%. After being exposed to air for 7 days, the water content was 0.3086%, the LiOH content was 0.4125%, and the Li2CO3 content was 0.4533%. Its first-cycle charge specific capacity was 243.9 mAh / g, its discharge specific capacity was 227.1 mAh / g, and its initial efficiency was 93.1%.

[0094] Comparative Example 1

[0095] This embodiment provides a method for preparing a high-nickel ternary cathode material without external coating, including the following steps:

[0096] (1) 3 kg of high-nickel ternary cathode material LiNi 0.92 Co 0.06 Mn 0.02 O2 is first dried in a vacuum drying oven at 90℃ for 0.5h, then premixed in a mixer at 800rpm for 2min. Then, 30mL of anhydrous ethanol is loaded into the container of a spraying device. The spraying device is connected to the mixing device. After premixing, the anhydrous ethanol in the spraying device container is sprayed from the nozzle onto the high-nickel ternary cathode material in the mixer. The spraying speed is controlled at 6mL / min, and the spraying time is about 5min. The mixture is stirred thoroughly while spraying. After spraying, the mixture is stirred for another 2min to ensure that the anhydrous ethanol and the high-nickel ternary cathode material are mixed evenly and in full contact. Finally, the mixture is placed in a vacuum drying oven at 110℃ for 2h to obtain a high-nickel ternary cathode material without an outer coating, which does not have hydrophobic properties.

[0097] Please see Figure 3 The mixer and spraying equipment used in this comparative experiment were the same as those used in Example 1.

[0098] Storage performance tests were conducted on the high-nickel ternary cathode material without an outer coating in Comparative Example 1: air exposure experiments were carried out in a normal atmospheric environment, and a portion of the samples were taken daily to test the water content, residual lithium content, and first-cycle capacity.

[0099] The results are as follows: Comparative Example 1 yielded a high-nickel ternary cathode material without external coating. Before exposure to air, the water content was 0.037%, the LiOH content was 0.5181%, and the Li2CO3 content was 0.2306%. The first-cycle charge specific capacity was 244.9 mAh / g, the discharge specific capacity was 228.6 mAh / g, and the initial efficiency was 93.3%. After being exposed to air for 7 days, the water content was 0.6876%, the LiOH content was 0.3619%, and the Li2CO3 content was 0.9304%. The first-cycle charge specific capacity was 239.8 mAh / g, the discharge specific capacity was 219.3 mAh / g, and the initial efficiency was 91.5%. The test results were compared with those of Examples 1-6.

[0100] test:

[0101] Battery Assembly and Testing: Lithium-ion coin cells were assembled in an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). The high-nickel ternary cathode material, conductive agent, and binder prepared in Examples 1-6 and Comparative Example 1 were mixed uniformly at a mass ratio of 90:5:5. A nitrogen-methylpyrrolidone solvent was added and stirred to form a slurry, which was then coated. After drying at 110°C for 2 hours, the slab was punched and dried again in a vacuum oven at 105°C for 4 hours. Coin cells were then assembled. The electrolyte was LiPF6 dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate. The separator was glass fiber, and the negative electrode was a lithium metal sheet. After assembly, the cells were allowed to stand for 3 hours before the first cycle test. The test conditions were: charge / discharge capacity and first-cycle efficiency at 0.1C at 25°C (1C = 210 mAh / g). Cycle performance testing was performed using all-electric coin cells, with the lithium metal negative electrode replaced by carbon material. The cycle stability of the cells was tested under 0.1C conditions.

[0102] The methods for preparing high-nickel ternary cathode materials with external coating provided in Examples 1-6 can synthesize high-nickel ternary cathode materials with external coating, significantly reducing the residual lithium content, surface water content, and residual alkali content of the high-nickel ternary cathode materials. Furthermore, the high-nickel ternary cathode materials with external coating still have a high first-cycle capacity retention rate after exposure to air, greatly improving the air storage performance and electrochemical performance of the high-nickel ternary cathode materials with external coating. The effects of this disclosure will be specifically explained below with reference to Comparative Example 1.

[0103] Please refer to Table 1, which shows the LiOH content and Li₂CO₃ content of the high-nickel ternary cathode materials obtained in Examples 1-6 and Comparative Example 1, and the residual Li. + The content data table shows that the high-nickel ternary cathode materials coated with the outer coating in Examples 1-6 have significantly lower residual alkali on their surface compared to Comparative Example 1.

[0104] Please refer to Table 2, which shows the first charge-discharge capacity data of the high-nickel ternary cathode materials obtained in Examples 1-6 and Comparative Example 1 under the condition of 4.3V / 0.1C. It can be seen from the table that the discharge specific capacity of the high-nickel ternary cathode materials obtained in Examples 1-6 is slightly lower than that of the high-nickel ternary cathode materials obtained in Comparative Example 1. This is attributed to the introduction of a small amount of silane coupling agent and lithium polyacrylate.

[0105] Please see Figure 1 The cycling performance of the high-nickel ternary cathode materials obtained in Examples 1-3 and Comparative Example 1 was compared. The capacity retention rates of Examples 1, 2, and 3 after 170 cycles were 83.7%, 80.7%, and 80.5%, respectively, while the capacity retention rate of Comparative Example 1 after 170 cycles was 76.6%, which is lower than the cycling performance of Examples 1-3.

[0106] Table 1

[0107]

[0108] Table 2

[0109]

[0110]

[0111] Please refer to Table 3, which shows the daily H2O content, LiOH content, and Li2CO3 content of the high-nickel ternary cathode materials obtained in Example 2 and Comparative Example 1 during the air exposure experiment. It can be seen from the table that as the number of days of exposure increases, the H2O content of Example 2 increases significantly less than that of Comparative Example 1, and the conversion of LiOH to Li2CO3 can be significantly suppressed in Example 2.

[0112] Table 3

[0113]

[0114] Please see Figure 2 The changes in the first discharge specific capacity of the high-nickel ternary cathode materials obtained in Example 3 and Comparative Example 1 during the air exposure experiment show that the discharge specific capacity of Example 3 is still 225.9 mAhg after 8 days of air exposure. -1 The capacity retention rate was 98.43%, while the discharge specific capacity of Comparative Example 1 after 8 days of air exposure was 213.2 mAh g. -1 The capacity retention rate was only 93.14%, which was significantly lower than that of Example 3.

[0115] Compared to related technologies, this disclosure combines inexpensive silane coupling agents and lithium polyacrylate with the surface of high-nickel ternary cathode materials using a simple device, significantly reducing residual alkali on the surface of the high-nickel ternary cathode materials and inhibiting the large-scale conversion of LiOH to Li2CO3. The residual alkali is rationally utilized to convert into a highly efficient coating that coats the surface of the high-nickel ternary cathode materials. The outer coating includes hydrophobic coatings of lithium organosilicon and lithium polyacrylate, effectively improving the processing performance and safety performance of the materials.

[0116] The embodiments described above are merely examples of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and this disclosure also intends to include these modifications and variations.

Claims

1. A method for preparing a high-nickel ternary cathode material with an outer coating, characterized in that: Includes the following steps: Preparation of silane coupling agent solution; Preparation of lithium polyacrylate solution; The high-nickel ternary cathode material is dried and then premixed in a mixer. After premixing, the silane coupling agent solution and the lithium polyacrylate solution are simultaneously sprayed onto the high-nickel ternary cathode material in the mixer through different nozzles while stirring. After spraying, a drying heat treatment is performed to obtain a high-nickel ternary cathode material with an outer coating. The amount of silane coupling agent in the silane coupling agent solution is 0.5% to 5% of the mass of the high-nickel ternary cathode material. The lithium polyacrylate in the lithium polyacrylate solution is obtained by reacting polyacrylic acid and lithium hydroxide, and the amount of polyacrylic acid is 0.5% to 3% of the mass of the high-nickel ternary cathode material.

2. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The silane coupling agent is prepared by dissolving the silane coupling agent in a first solvent to obtain the silane coupling agent solution.

3. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 2, characterized in that: The chemical formula of the silane coupling agent is YSiX3, where Y is a hydrophobic functional group, which is one of hydrocarbon group, ester group, phenyl group, and fluorophenyl group; and X is a hydrolyzable group, which is one of methoxy group, halogen group, ethoxy group, and acetoxy group.

4. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 3, characterized in that: Y is one of methyl, propyl, phenyl, butyl, octyl, or vinyl.

5. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 2, characterized in that: The first solvent is a volatile organic solvent, such as anhydrous ethanol, anhydrous methanol, or acetone, or one or more of these.

6. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The method for preparing the lithium polyacrylate solution is as follows: polyacrylic acid and lithium hydroxide are dissolved in a second solvent to obtain a lithium polyacrylate solution, wherein the pH of the lithium polyacrylate solution is 5-9.

7. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 6, characterized in that: The molecular weight of the polyacrylic acid is 250,000 to 500,000.

8. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 6, characterized in that: The second solvent is one or more of water, anhydrous ethanol, and isopropanol.

9. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The volume concentration of the silane coupling agent solution is 10-100%; the volume concentration of the lithium polyacrylate solution is 10-100%.

10. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The chemical formula for the high-nickel ternary cathode material is LiNi. x Co y M z O2, where M is element Mn or element Al; x takes values ​​from 0.7 to 1.0, y takes values ​​from 0 to 0.3, z takes values ​​from 0 to 0.3, and x + y + z = 1.

11. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The drying conditions for the high-nickel ternary cathode material are as follows: drying in a vacuum oven at a temperature of 90℃~180℃ for 0.5~3 hours.

12. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: First, the silane coupling agent solution and the lithium polyacrylate solution are respectively loaded into different spray equipment containers. Then, after the high-nickel ternary cathode material is premixed, the silane coupling agent solution and the lithium polyacrylate solution are simultaneously sprayed onto the high-nickel ternary cathode material in the mixer at different nozzles.

13. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The mixer operates at a speed of 300-1200 rpm and a premixing time of 1-10 minutes.

14. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 12, characterized in that: The spraying conditions for both the silane coupling agent solution and the lithium polyacrylate solution on the spraying equipment are as follows: spraying speed of 5-50 ml / min and spraying time of 2-15 minutes.

15. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: Stirring time is 1 to 10 minutes.

16. The method for preparing the high-nickel ternary cathode material with an outer coating according to claim 1, characterized in that: The drying heat treatment conditions are oven drying at a temperature of 90~150℃ for 2~24 hours.

17. A high-nickel ternary cathode material with an outer coating, characterized in that: It is obtained by any of the preparation methods of high-nickel ternary cathode materials with external coating as described in 1 to 16.

Images