High-nickel ternary positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a high-nickel ternary positive electrode material and a preparation method and application thereof, and belongs to the technical field of batteries and battery materials, a coating layer is formed on the surface of the high-nickel ternary positive electrode material through silicon dioxide, direct contact between an electrode material and an electrolyte is effectively isolated, and then through a thiol-ene click reaction, the high-nickel ternary positive electrode material is obtained. The graphene / titanium dioxide core-shell whisker is used as a reinforcing phase to coat the surface of the silicon dioxide coating layer again, so that the interface bonding force between the two coating layers is increased, the volume change caused by lithium ion intercalation and deintercalation can be coped, the structural stability of the material is kept, and the specific discharge capacity, the capacity retention rate and the cycling stability are favorably improved; according to the graphene / titanium dioxide core-shell whisker, titanium dioxide containing whiskers is synthesized on the surface of graphene containing a lamellar structure through microwave heating and serves as a core layer, then a shell-structure lanthanum metal framework is synthesized in a hydro-thermal mode, and the interface bonding force can be further improved through the mechanical interlocking effect.

Description

Technical Field

[0001] This invention belongs to the field of battery and battery material technology, specifically a high-nickel ternary cathode material, its preparation method, and its application. Background Technology

[0002] High-nickel layered cathode materials have attracted widespread attention due to their advantages of high specific capacity, battery energy density, and low cost. However, as the nickel content increases, material preparation and storage become more complex, and charge-discharge cycle performance and thermal stability decrease accordingly, thus affecting battery cycle life and safety. The main adverse factors affecting the application of high-nickel layered cathode materials are surface pH and electrode / electrolyte interface stability. First, the high pH value of the material surface easily reacts with water and carbon dioxide in the air during storage, causing gas expansion during battery cycling and leading to water absorption and gelation of the electrode slurry, resulting in losses. Second, the electrode / electrolyte interface of ternary materials is unstable, especially the transition metal at the surface interface, which is prone to dissolution and phase transition, causing cathode cycle degradation.

[0003] High-nickel layered cathode materials are excellent cathode materials, and have already achieved commercial applications due to their high capacity and good rate performance. However, the poor cycle performance of NCMs severely hinders their further commercial application. Research shows that coating technology is an effective means to improve the cycle performance of NCMs. Low-cost, high-performance coating materials are a key focus of attention. Solid electrolytes have attracted widespread attention due to their good lithium-ion diffusion coefficient, excellent thermal stability, and structural stability; for example, the solid electrolyte Li4SiO4 can be used as a cathode material.

[0004] Chinese patent application CN119911987A discloses a high-nickel ternary cathode material with silicon electrolyte coating, its preparation method, and a battery. In this scheme, graphene-modified titanium dioxide powder is added to tetraethyl orthosilicate solution when coating the high-nickel ternary cathode material precursor to provide structural support for the cathode material. During the lithium-ion insertion / extraction process, the stress generated by the volume change is partially buffered by the composite structure of titanium dioxide and graphene, reducing the pulverization and structural damage of the high-nickel ternary cathode material. However, in this scheme, the graphene-modified titanium dioxide is only coated on the silicon dioxide layer by physical stirring, which cannot form a good interfacial bond, making it easy for the graphene-modified titanium dioxide layer to fall off during volume expansion. Summary of the Invention

[0005] The purpose of this invention is to provide a high-nickel ternary cathode material, its preparation method, and its application. A coating layer is formed on the surface of the high-nickel ternary cathode material using silicon dioxide, which effectively isolates the electrode material from direct contact with the electrolyte. Then, through a mercapto-alkene click reaction, graphene / titanium dioxide core-shell whiskers are used as a reinforcing phase to coat the surface of the silicon dioxide coating layer again, increasing the interfacial bonding force between the two coating layers. This can cope with the volume changes caused by lithium-ion insertion and extraction, maintain the structural stability of the material, and is beneficial to improving the discharge specific capacity, capacity retention rate, and cycle stability.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a high-nickel ternary cathode material includes the following steps: Step 1: Tetraisopropyl phthalate is hydrolyzed to generate titanium glycolate white flocculent precipitate. Then, microwave heating is used to promote the directional growth of the white flocculent precipitate along the graphene surface to form graphene / titanium dioxide whisker precursor. After calcination, graphene / titanium dioxide whiskers are obtained.

[0007] Step 2: A lanthanum metal framework is grown on the surface of graphene / titanium dioxide whiskers by hydrothermal coordination of lanthanum metal with 4-vinylbenzoic acid, thus obtaining graphene / titanium dioxide core-shell whiskers.

[0008] Step 3: Using the sol-gel method, on LiNi 0.9 Co 0.05 Mn 0.05 O2 generates silica on the surface, resulting in silica-coated high-nickel materials; by condensing the hydroxyl groups on the surface of the silica-coated high-nickel materials with γ-mercaptopropyltrimethoxysilane, thiolized silica-coated high-nickel materials are prepared.

[0009] Step 4: High-nickel ternary cathode material is obtained by reacting high-nickel material coated with thiolized silica with graphene / titanium dioxide core-shell whiskers under the action of initiator 2,2-dimethylolpropionic acid.

[0010] Furthermore, the specific preparation steps of the graphene / titanium dioxide whisker precursor are as follows: Ethylene glycol and a graphene dispersion with a concentration of 2 mg / mL were added to a reaction vessel, and nitrogen gas was introduced to remove air from the reaction vessel. Then, tetraisopropyl phthalate was added, and the mixture was stirred for 10-12 min at 20-25 °C and 500-600 r / min. The mixture was then placed in a microwave heating device and heated for 2-3 min at 700 W and 2.45 GHz. The tetraisopropyl phthalate hydrolyzed to form a white flocculent precipitate of titanium glycol. The precipitate was filtered, and the filter cake was washed 2-4 times with deionized water and ethanol, respectively. The precipitate was then vacuum dried at 60-70 °C for 1-2 h to obtain the graphene / titanium dioxide whisker precursor.

[0011] Furthermore, the ratio of ethylene glycol, graphene dispersion, and tetraisopropyl phthalate is 1000-1200 mL: 200-300 mL: 20-30 mL.

[0012] Furthermore, the specific preparation steps for graphene / titanium dioxide whiskers are as follows: The graphene / titanium dioxide whisker precursor was placed in a muffle furnace and heated to 500-520℃ under nitrogen protection and a heating rate of 10-12℃ / min, and held for 2-3 hours to obtain graphene / titanium dioxide whiskers.

[0013] Furthermore, the specific preparation steps for graphene / titanium dioxide core-shell whiskers are as follows: Lanthanum nitrate, 4-vinylbenzoic acid, and N,N-dimethylformamide were added to a reaction vessel and stirred for 10-12 minutes at 20-25°C and 500-600 r / min. Then, deionized water and graphene / titanium dioxide whiskers were added, and the mixture was heated to 70-75°C and allowed to stand for 24-26 hours. After naturally cooling to room temperature, the mixture was centrifuged at 8000-8500 r / min for 3-5 minutes, filtered, and the precipitate was washed 2-4 times with methanol. Then, the precipitate was solvent-exchanged with chloroform and soaked for another 24-26 hours at 20-25°C. Finally, it was vacuum dried at 60-70°C for 1-2 hours to obtain graphene / titanium dioxide core-shell whiskers.

[0014] Furthermore, the ratio of lanthanum nitrate, 4-vinylbenzoic acid, N,N-dimethylformamide, deionized water, graphene / titanium dioxide whiskers, methanol, and chloroform is 15-20g: 5-7g: 550-650mL: 250-270mL: 20-22g: 500-600mL: 500-600mL.

[0015] Furthermore, the specific preparation steps for silica-coated high-nickel materials are as follows: LiNi 0.9 Co 0.05 Mn 0.05 O2 and deionized water are added to the reactor and stirred for 10-12 minutes at 20-25℃ and 500-600 r / min. Then, tetraethyl orthosilicate and ethanol are added, and the mixture is heated to 50-60℃ and stirred for 1-2 hours. The mixture is then heated to 80-85℃ and stirred until the ethanol is completely evaporated. The mixture is filtered, and the filter cake is washed 2-4 times with deionized water and dried under vacuum at 60-70℃ for 1-2 hours to obtain silica-coated high-nickel material.

[0016] Furthermore, LiNi 0.9 Co 0.05 Mn 0.05The ratio of O2, deionized water, tetraethyl orthosilicate and ethanol is 60-70g: 250-300mL: 4-5g: 300-400mL.

[0017] Furthermore, the specific preparation steps for thiolized silica-coated high-nickel materials are as follows: High-nickel silica-coated material, ethanol, and deionized water were added to a reaction vessel and stirred for 10-12 minutes at 20-25°C and 500-600 rpm. The pH was then adjusted to 4-5 with hydrochloric acid, followed by the addition of γ-mercaptopropyltrimethoxysilane. The mixture was heated to 80-90°C and stirred for 12-14 hours. After centrifugation at 8000-8500 rpm for 3-5 minutes, the mixture was filtered. The precipitate was washed 2-4 times with deionized water and anhydrous ethanol, and then vacuum dried at 60-70°C for 1-2 hours to obtain the mercapto-coated high-nickel silica material.

[0018] Furthermore, the ratio of silica-coated high-nickel material, ethanol, deionized water, and γ-mercaptopropyltrimethoxysilane is 50-60g: 2-3L: 1-1.2L: 200-300mL.

[0019] Furthermore, the specific preparation steps for high-nickel ternary cathode materials are as follows: Thiol-coated silica high-nickel material, graphene / titanium dioxide core-shell whiskers, 2,2-dimethylolpropionic acid and tetrahydrofuran were added to a reactor and stirred for 10-12 min at 20-25℃ and 500-600 r / min. Then, the mixture was cured for 6-7 h at a wavelength of 365 nm and an intensity of 6 mW / cm. After filtration, the precipitate was washed 2-4 times with deionized water and anhydrous ethanol, and then dried under vacuum at 60-70℃ for 1-2 h to obtain the high-nickel ternary cathode material.

[0020] Furthermore, the ratio of mercapto-modified silica-coated high-nickel material, graphene / titanium dioxide core-shell whiskers, 2,2-dimethylolpropionic acid, and tetrahydrofuran is 10-20g: 5-7g: 0.8-0.9g: 500-600mL.

[0021] The present invention also provides an application of a high-nickel ternary cathode material in lithium batteries.

[0022] The beneficial effects of this invention are: 1. The present invention provides a high-nickel ternary cathode material. A coating layer of silicon dioxide is formed on the surface of the high-nickel ternary cathode material to effectively isolate the electrode material from direct contact with the electrolyte. Then, through a mercapto-alkene click reaction, graphene / titanium dioxide core-shell whiskers are used as a reinforcing phase to coat the surface of the silicon dioxide coating layer again, increasing the interfacial bonding force between the two coating layers. This can cope with the volume changes caused by lithium ion insertion and extraction, maintain the structural stability of the material, and is beneficial to improving the discharge specific capacity, capacity retention rate, and cycle stability.

[0023] 2. The graphene / titanium dioxide core-shell whiskers of the present invention are synthesized hydrothermally on the surface of graphene / titanium dioxide whiskers using a lanthanum metal framework with 4-vinylbenzoic acid as the monomer and lanthanum as the metal source. This differs from traditional direct physical mixing. When lanthanum is uniformly incorporated into the lattice of the high-nickel ternary cathode material, lanthanum ions typically occupy some lattice positions of nickel, cobalt, and manganese. Since the ionic radius of lanthanum ions is usually larger than that of nickel ions, its doping can expand the lattice volume. This lattice expansion alleviates the volume change caused by lithium ions during insertion and extraction to a certain extent, reducing the structural stress of the cathode material. The lanthanum metal framework contains double bonds, which can serve as initiation sites for mercapto-alkene click reactions, thus fixing the graphene / titanium dioxide core-shell whiskers onto the mercapto-coated high-nickel material.

[0024] 3. The graphene / titanium dioxide core-shell whiskers of the present invention are synthesized by microwave heating on the surface of graphene containing a sheet structure to form a whisker-containing titanium dioxide core layer, and then a lanthanum metal framework with a shell structure is synthesized by hydrothermal synthesis. The whisker structure can further improve the interfacial bonding force between the graphene / titanium dioxide core-shell whiskers and the mercapto-coated high-nickel material through a mechanical interlocking effect. The lanthanum metal framework, as a bridge, can alleviate volume changes by generating relative slip dispersion stress due to its special structure.

[0025] 4. This invention synthesizes titanium dioxide containing whiskers through microwave heating. When a mixed solution of tetraisopropyl phthalate and ethylene glycol is irradiated by microwaves, the −OH group in the ethylene glycol undergoes violent antisymmetric vibrations, instantly generating a large amount of heat energy. When the molecular thermal motion reaches a certain level, the hydrolysis reaction between tetraisopropyl phthalate and ethylene glycol begins, generating chain-like titanium glycolate complexes. Under the van der Waals forces between the methyl groups, the chain-like products tend to aggregate into bundles, forming a locally supersaturated solution and precipitating relatively stable titanium glycolate primary particles. Under continuous microwave irradiation, these amorphous primary particles further crystallize and nucleate, forming a large number of fine crystalline particles. In this process, graphene, as a carrier, can efficiently absorb microwave energy and convert it into heat energy, promoting the formation of titanium dioxide whiskers. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 A method for preparing a high-nickel ternary cathode material includes the following steps: S1: 1000 mL of ethylene glycol and 200 mL of graphene dispersion with a concentration of 2 mg / mL were added to a reaction vessel. Nitrogen gas was introduced to remove air from the reaction vessel. Then, 20 mL of tetraisopropyl phthalate was added. The mixture was stirred for 10 min at 20 °C and 500 r / min. Then, it was placed in a microwave heating device and heated for 2 min at 700 W and 2.45 GHz. The tetraisopropyl phthalate hydrolyzed to generate titanium glycolate white flocculent precipitate. The precipitate was filtered, and the filter cake was washed twice with deionized water and ethanol, respectively. It was then vacuum dried at 60 °C for 1 h to obtain graphene / titanium dioxide whisker precursor. The graphene / titanium dioxide whisker precursor was placed in a muffle furnace and heated to 500 °C under nitrogen protection and a heating rate of 10 °C / min. The temperature was maintained for 2 h to obtain graphene / titanium dioxide whiskers.

[0028] S2: Add 15g lanthanum nitrate, 5g 4-vinylbenzoic acid and 550mL N,N-dimethylformamide to a reaction vessel, stir for 10min at 20℃ and 500r / min, then add 250mL deionized water and 20g graphene / titanium dioxide whiskers, heat to 70℃, let stand for 24h, cool naturally to room temperature, centrifuge at 8000r / min for 3min, filter, wash the precipitate twice with 500mL methanol, then exchange the solvent with 500mL chloroform, continue soaking at 20℃ for 24h, and vacuum dry at 60℃ for 1h to obtain graphene / titanium dioxide core-shell whiskers.

[0029] S3: Add 60g LiNi 0.9 Co 0.05 Mn 0.05 O2 and 250 mL of deionized water were added to the reaction vessel and stirred for 10 min at 20 °C and 500 r / min. Then, 4 g of tetraethyl orthosilicate and 300 mL of ethanol were added, and the mixture was heated to 50 °C and stirred for 1 h. The mixture was then heated to 80 °C and stirred until the ethanol was completely evaporated. The mixture was filtered, and the filter cake was washed twice with deionized water and dried under vacuum at 60 °C for 1 h to obtain silica-coated high-nickel material.

[0030] S4: Add 50g of silica-coated high-nickel material, 2L of ethanol and 1L of deionized water to a reaction vessel, stir for 10min at 20℃ and 500r / min, then adjust the pH to 4 with hydrochloric acid, add 200mL of γ-mercaptopropyltrimethoxysilane, heat to 80℃, continue stirring for 12h, centrifuge at 8000r / min for 3min, filter, wash the precipitate twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 60℃ for 1h to obtain mercapto-coated silica-coated high-nickel material.

[0031] S5: 10g of mercapto-modified silica-coated high-nickel material, 5g of graphene / titanium dioxide core-shell whiskers, 0.8g of photoinitiator 2,2-dimethylolpropionic acid, and 500mL of tetrahydrofuran were added to a reactor and stirred for 10min at 20℃ and 500r / min. Then, the mixture was cured for 6h at a wavelength of 365nm and a light intensity of 6mW / cm. After filtration, the precipitate was washed twice with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 60℃ for 1h to obtain the high-nickel ternary cathode material.

[0032] Example 2 A method for preparing a high-nickel ternary cathode material includes the following steps: S1: 1100 mL of ethylene glycol and 250 mL of graphene dispersion with a concentration of 2 mg / mL were added to a reaction vessel. Nitrogen gas was introduced to remove air from the reaction vessel. Then, 25 mL of tetraisopropyl phthalate was added. The mixture was stirred for 11 min at 22.5 °C and 550 r / min. Then, it was placed in a microwave heating device and heated for 2.5 min at 700 W and 2.45 GHz. The tetraisopropyl phthalate was hydrolyzed to generate titanium glycolate, a white flocculent precipitate. The precipitate was filtered, and the filter cake was washed three times with deionized water and ethanol, respectively. It was then vacuum dried at 65 °C for 1.5 h to obtain graphene / titanium dioxide whisker precursor. The graphene / titanium dioxide whisker precursor was placed in a muffle furnace and heated to 510 °C under nitrogen protection and a heating rate of 11 °C / min. The temperature was maintained for 2.5 h to obtain graphene / titanium dioxide whiskers.

[0033] S2: 17.5g lanthanum nitrate, 6g 4-vinylbenzoic acid and 600mL N,N-dimethylformamide were added to a reaction vessel and stirred for 11min at 22.5℃ and 550r / min. Then 260mL deionized water and 21g graphene / titanium dioxide whiskers were added, heated to 72.5℃, allowed to stand for 25h, and allowed to cool naturally to room temperature. The mixture was centrifuged at 8250r / min for 4min, filtered, and the precipitate was washed three times with 550mL methanol and then solvent exchanged with 550mL chloroform. The mixture was soaked at 22.5℃ for 25h and then vacuum dried at 65℃ for 1.5h to obtain graphene / titanium dioxide core-shell whiskers.

[0034] S3: Add 65g LiNi 0.9 Co 0.05 Mn 0.05 O2 and 275 mL of deionized water were added to the reactor and stirred for 11 min at 22.5 °C and 550 r / min. Then, 4.5 g of tetraethyl orthosilicate and 350 mL of ethanol were added, and the mixture was heated to 55 °C and stirred for 1.5 h. The mixture was then heated to 82.5 °C and stirred until the ethanol was completely evaporated. The mixture was filtered, and the filter cake was washed three times with deionized water and dried under vacuum at 65 °C for 1.5 h to obtain silica-coated high-nickel material.

[0035] S4: Add 55g of silica-coated high-nickel material, 2.5L of ethanol and 1.1L of deionized water to a reaction vessel, stir for 11min at 22.5℃ and 550r / min, then adjust the pH to 4.5 with hydrochloric acid, add 250mL of γ-mercaptopropyltrimethoxysilane, heat to 85℃, continue stirring for 13h, centrifuge at 8250r / min for 4min, filter, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 65℃ for 1.5h to obtain mercapto-coated silica-coated high-nickel material.

[0036] S5: 15g of mercapto-modified silica-coated high-nickel material, 6g of graphene / titanium dioxide core-shell whiskers, 0.85g of photoinitiator 2,2-dimethylolpropionic acid, and 550mL of tetrahydrofuran were added to a reactor and stirred for 11min at 22.5℃ and 550r / min. Then, the mixture was cured for 6.5h at a wavelength of 365nm and a light intensity of 6mW / cm. After filtration, the precipitate was washed three times with deionized water and anhydrous ethanol, and then dried under vacuum at 65℃ for 1.5h to obtain the high-nickel ternary cathode material.

[0037] Example 3 A method for preparing a high-nickel ternary cathode material includes the following steps: S1: 1200 mL of ethylene glycol and 300 mL of graphene dispersion with a concentration of 2 mg / mL were added to a reaction vessel. Nitrogen gas was introduced to remove air from the reaction vessel. Then, 30 mL of tetraisopropyl phthalate was added. The mixture was stirred for 12 min at 25 °C and 600 r / min. Then, it was placed in a microwave heating device and heated for 3 min at 700 W and 2.45 GHz. The tetraisopropyl phthalate hydrolyzed to generate titanium glycolate white flocculent precipitate. The precipitate was filtered, and the filter cake was washed four times with deionized water and ethanol, respectively. It was then vacuum dried at 70 °C for 2 h to obtain graphene / titanium dioxide whisker precursor. The graphene / titanium dioxide whisker precursor was placed in a muffle furnace and heated to 520 °C under nitrogen protection and a heating rate of 12 °C / min. The temperature was maintained for 3 h to obtain graphene / titanium dioxide whiskers.

[0038] S2: Add 20g lanthanum nitrate, 7g 4-vinylbenzoic acid and 650mL N,N-dimethylformamide to a reaction vessel and stir for 12min at 25℃ and 600r / min. Then add 270mL deionized water and 22g graphene / titanium dioxide whiskers, heat to 75℃, let stand for 26h, cool naturally to room temperature, centrifuge at 8500r / min for 5min, filter, wash the precipitate 4 times with 600mL methanol, then exchange the solvent with 600mL chloroform, continue soaking at 25℃ for 26h, and vacuum dry at 70℃ for 2h to obtain graphene / titanium dioxide core-shell whiskers.

[0039] S3: Add 70g LiNi 0.9 Co 0.05 Mn 0.05 O2 and 300 mL of deionized water were added to the reactor and stirred for 12 min at 25 °C and 600 r / min. Then, 5 g of tetraethyl orthosilicate and 400 mL of ethanol were added, and the mixture was heated to 60 °C and stirred for 2 h. The mixture was then heated to 85 °C and stirred until the ethanol was completely evaporated. The mixture was filtered, and the filter cake was washed four times with deionized water and dried under vacuum at 70 °C for 2 h to obtain silica-coated high-nickel material.

[0040] S4: Add 60g of silica-coated high-nickel material, 3L of ethanol and 1.2L of deionized water to a reaction vessel, stir for 12min at 25℃ and 600r / min, then adjust the pH to 5 with hydrochloric acid, add 300mL of γ-mercaptopropyltrimethoxysilane, heat to 90℃, continue stirring for 14h, centrifuge at 8500r / min for 5min, filter, wash the precipitate 4 times with deionized water and anhydrous ethanol respectively, and vacuum dry at 70℃ for 2h to obtain mercapto-coated silica-coated high-nickel material.

[0041] S5: 20g of mercapto-modified silica-coated high-nickel material, 7g of graphene / titanium dioxide core-shell whiskers, 0.9g of photoinitiator 2,2-dimethylolpropionic acid, and 600mL of tetrahydrofuran were added to a reactor and stirred for 12min at 25℃ and 600r / min. Then, the mixture was cured for 7h at a wavelength of 365nm and a light intensity of 6mW / cm. After filtration, the precipitate was washed four times with deionized water and anhydrous ethanol, and then dried under vacuum at 70℃ for 2h to obtain the high-nickel ternary cathode material.

[0042] Comparative Example 1 Based on Example 3, 4-vinylbenzoic acid in step S2 was omitted, while the remaining steps remained unchanged, to prepare a high-nickel ternary cathode material.

[0043] Comparative Example 2 Based on Example 3, the microwave heating device in step S1 was removed so that it could not generate graphene / titanium dioxide whisker precursors, while the other steps remained unchanged, and a high-nickel ternary cathode material was prepared.

[0044] Comparative Example 3 Based on Example 3, the high-nickel ...

[0045] In the examples and comparative examples: LiNi 0.9 Co 0.05 Mn 0.05 O2 is selected from the preparation method of high-nickel ternary cathode material and the prepared high-nickel ternary cathode material disclosed in Chinese patent application CN114538532A, as described in paragraph 25 of the specification.

[0046] Tetraisopropylphthalate was purchased from Sigma-Aldrich, CAS No.: 546-68-9.

[0047] 4-Vinylbenzoic acid was purchased from Sigma-Aldrich, CAS No.: 1075-49-6.

[0048] 2,2-Dimethylolpropionic acid was purchased from Sigma-Aldrich, CAS No.: 10097-02-6.

[0049] The performance of the high-nickel ternary cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 was tested. High-nickel ternary cathode materials, carbon black, and polyvinylidene fluoride were added to a methylpyrrolidone solution in a ratio of 8:1:1 to prepare a cathode slurry. The obtained cathode slurry was then adhered to aluminum foil and dried overnight in a vacuum oven at 120°C. The electrode was assembled into a button cell in an argon-filled glove box, using a Celgard 2400 film as the separator, lithium metal foil as the negative electrode, and 1M LiPF6 (EC:DMC:EMC=1:1:1 Vol%) as the electrolyte, with a volume of 0.2 mL. The initial discharge specific capacity and capacity retention at 0.2C and 1C rates were tested, and the results are shown in Table 1.

[0050] Table 1 As can be seen from Table 1, the discharge specific capacity, discharge specific capacity after 120 cycles, and capacity retention rate of the high-nickel ternary cathode materials prepared in Examples 1-3 are significantly better than those of the comparative examples, indicating that the high-nickel ternary cathode materials prepared in this invention have good discharge specific capacity, capacity retention rate, and cycle stability.

[0051] In Comparative Example 1, 4-vinylbenzoic acid is a dual-functional carrier. First, it participates in the construction of the lanthanum metal framework as an organic ligand. Second, it provides the carbon-carbon double bond as the sole site for the thiol-alkene click reaction. Without this substance, lanthanum can only exist in a free state or in the form of amorphous oxide, and cannot form a uniform metal framework. At the same time, the graphene / titanium dioxide core-shell whisker surface has no reaction sites and cannot form covalent cross-links with the thiolized silica coating layer, but can only be bound by physical adsorption. The free lanthanum cannot be uniformly incorporated into the high-nickel lattice, and there is only a lattice expansion effect in local areas, which cannot alleviate the overall volume change. The structural stress concentration leads to the pulverization of the material. The lack of the lanthanum metal framework leads to poor dispersion of the core-shell whiskers, discontinuity of the graphene conductive network, increased electron transport resistance, and decreased utilization of active sites.

[0052] In Comparative Example 2, microwave heating is the key driving force for the directional growth of titanium dioxide whiskers. The high dielectric loss characteristics of graphene enable it to generate heat rapidly in the microwave field, forming local hot spots that induce the directional polymerization and crystallization of tetraisopropyl phthalate hydrolysis products into whiskers. After removing the microwave, conventional heating alone cannot form a local supersaturated environment, so titanium dioxide can only be deposited on the graphene surface in the form of amorphous particles or irregular crystals, and cannot form a whisker structure.

[0053] In Comparative Example 3, the core function of γ-mercaptopropyltrimethoxysilane modification is to provide thiol active sites for the silica coating layer, which undergo thiol-alkene click reaction with the double bonds on the surface of the core-shell whiskers to form stable covalent bonds. The surface of the unthiolized silica coating layer has only a small amount of hydroxyl groups remaining, which cannot form chemical bonds with the core-shell whiskers and can only be bonded by weak hydrogen bonds or van der Waals forces.

[0054] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-nickel ternary cathode material, characterized in that, Includes the following steps: Step 1: Tetraisopropyl phthalate is hydrolyzed to generate titanium glycol white flocculent precipitate. Then, microwave heating is used to promote the directional growth of the white flocculent precipitate along the graphene surface to form graphene / titanium dioxide whisker precursor. After calcination, graphene / titanium dioxide whiskers are obtained. Step 2: A lanthanum metal framework is grown on the surface of graphene / titanium dioxide whiskers by hydrothermal coordination of lanthanum metal with 4-vinylbenzoic acid, thus obtaining graphene / titanium dioxide core-shell whiskers. Step 3: Using the sol-gel method, on LiNi 0.9 Co 0.05 Mn 0.05 O2 generates silica on the surface, resulting in silica-coated high-nickel materials; by condensing the hydroxyl groups on the surface of the silica-coated high-nickel materials with γ-mercaptopropyltrimethoxysilane, mercapto-modified silica-coated high-nickel materials are prepared. Step 4: High-nickel ternary cathode material is obtained by reacting high-nickel material coated with thiolized silica with graphene / titanium dioxide core-shell whiskers under the action of initiator 2,2-dimethylolpropionic acid.

2. The method for preparing a high-nickel ternary cathode material according to claim 1, characterized in that, The specific preparation steps of the graphene / titanium dioxide whisker precursor are as follows: Ethylene glycol and a graphene dispersion with a concentration of 2 mg / mL were added to a reaction vessel, and nitrogen gas was introduced to remove air from the reaction vessel. Then, tetraisopropyl phthalate was added, and the mixture was stirred for 10-12 min at 20-25 °C and 500-600 r / min. The mixture was then placed in a microwave heating device and heated for 2-3 min at 700 W and 2.45 GHz. The tetraisopropyl phthalate hydrolyzed to form a white flocculent precipitate of titanium glycol. The precipitate was filtered, and the filter cake was washed 2-4 times with deionized water and ethanol, respectively. The filter cake was then vacuum dried at 60-70 °C for 1-2 h to obtain the graphene / titanium dioxide whisker precursor. The ratio of ethylene glycol, graphene dispersion, and tetraisopropyl phthalate is 1000-1200 mL: 200-300 mL: 20-30 mL.

3. The method for preparing a high-nickel ternary cathode material according to claim 1, characterized in that, The specific preparation steps for the graphene / titanium dioxide whiskers are as follows: The graphene / titanium dioxide whisker precursor was placed in a muffle furnace and heated to 500-520℃ under nitrogen protection and a heating rate of 10-12℃ / min, and held for 2-3 hours to obtain graphene / titanium dioxide whiskers.

4. The method for preparing a high-nickel ternary cathode material according to claim 1, characterized in that, The specific preparation steps for the graphene / titanium dioxide core-shell whiskers are as follows: Lanthanum nitrate, 4-vinylbenzoic acid, and N,N-dimethylformamide were added to a reaction vessel and stirred for 10-12 minutes at 20-25°C and 500-600 r / min. Then, deionized water and graphene / titanium dioxide whiskers were added, and the mixture was heated to 70-75°C and allowed to stand for 24-26 hours. After naturally cooling to room temperature, the mixture was centrifuged at 8000-8500 r / min for 3-5 minutes, filtered, and the precipitate was washed 2-4 times with methanol. Then, the precipitate was solvent-exchanged with chloroform and soaked for another 24-26 hours at 20-25°C. Finally, it was vacuum dried at 60-70°C for 1-2 hours to obtain graphene / titanium dioxide core-shell whiskers.

5. The method for preparing a high-nickel ternary cathode material according to claim 4, characterized in that, The ratio of lanthanum nitrate, 4-vinylbenzoic acid, N,N-dimethylformamide, deionized water, graphene / titanium dioxide whiskers, methanol, and chloroform is 15-20g: 5-7g: 550-650mL: 250-270mL: 20-22g: 500-600mL: 500-600mL.

6. The method for preparing a high-nickel ternary cathode material according to claim 1, characterized in that, The specific preparation steps for the silica-coated high-nickel material are as follows: LiNi 0.9 Co 0.05 Mn 0.05 O2 and deionized water are added to the reaction vessel and stirred for 10-12 minutes at 20-25℃ and 500-600 r / min. Then, tetraethyl orthosilicate and ethanol are added, and the mixture is heated to 50-60℃ and stirred for 1-2 hours. The mixture is then heated to 80-85℃ and stirred until the ethanol is completely evaporated. The mixture is filtered, and the filter cake is washed 2-4 times with deionized water and dried under vacuum at 60-70℃ for 1-2 hours to obtain silica-coated high-nickel material. The LiNi 0.9 Co 0.05 Mn 0.05 The ratio of O2, deionized water, tetraethyl orthosilicate and ethanol is 60-70g: 250-300mL: 4-5g: 300-400mL.

7. The method for preparing a high-nickel ternary cathode material according to claim 1, characterized in that, The specific preparation steps for the mercapto-coated high-nickel material are as follows: High-nickel silica-coated material, ethanol, and deionized water were added to a reaction vessel and stirred for 10-12 minutes at 20-25°C and 500-600 r / min. The pH was then adjusted to 4-5 with hydrochloric acid, and γ-mercaptopropyltrimethoxysilane was added. The mixture was heated to 80-90°C and stirred for 12-14 hours. After centrifugation at 8000-8500 r / min for 3-5 minutes, the mixture was filtered. The precipitate was washed 2-4 times with deionized water and anhydrous ethanol, and then vacuum dried at 60-70°C for 1-2 hours to obtain the mercapto-coated high-nickel silica material. The ratio of the amount of silica-coated high-nickel material, ethanol, deionized water and γ-mercaptopropyltrimethoxysilane is 50-60g: 2-3L: 1-1.2L: 200-300mL.

8. The method for preparing a high-nickel ternary cathode material according to claim 1, characterized in that, The specific preparation steps of the high-nickel ternary cathode material are as follows: Thiol-coated silica high-nickel material, graphene / titanium dioxide core-shell whiskers, 2,2-dimethylolpropionic acid and tetrahydrofuran were added to a reactor and stirred for 10-12 min at 20-25℃ and 500-600 r / min. Then, the mixture was cured for 6-7 h at a wavelength of 365 nm and a light intensity of 6 mW / cm. After filtration, the precipitate was washed 2-4 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70℃ for 1-2 h to obtain high-nickel ternary cathode material. The ratio of the amount of the thiolized silica-coated high-nickel material, graphene / titanium dioxide core-shell whiskers, 2,2-dimethylolpropionic acid and tetrahydrofuran is 10-20g: 5-7g: 0.8-0.9g: 500-600mL.

9. A high-nickel ternary cathode material, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of a high-nickel ternary cathode material according to claim 9 in lithium batteries.

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