Positive electrode material, preparation method, and use

Abstract

A positive electrode material, a preparation method for a positive electrode material, and a use of a positive electrode material. The positive electrode material comprises titanium dioxide coated on a ternary material, and polydimethylsiloxane is grafted onto the titanium dioxide to form a hydrophobic layer. In one aspect, the hydrophobic layer can physically isolate the ternary material from reacting with water and carbon dioxide in the air. In another aspect, when polydimethylsiloxane is grafted onto titanium dioxide, the connection by means of chemical bonds between the two can form a hydrophobic layer more stable than by bonding or in similar approaches. Moreover, a hydrophobic layer formed by polydimethylsiloxane being grafted onto titanium dioxide, compared with directly using siloxane to modify a ternary material, has better hydrophobicity, and more stable durability in long-term electrolyte infiltration, preventing the reaction of HF acid with titanium dioxide or a positive electrode material in the electrolyte, thus enhancing the chemical stability of the positive electrode material as well as battery safety.

Description

Positive electrode materials, preparation methods and applications Technical Field

[0001] The present disclosure relates to the technical field of positive electrode materials, and in particular to positive electrode materials, preparation methods and applications. Background Art

[0002] Ternary cathode materials have the advantages of high platform potential, high energy density and low cost, and have broad application prospects in the power lithium-ion battery market. However, ternary materials have the problem of a large amount of residual lithium on the surface. The residual lithium easily reacts with CO2 and H=O in the air to generate Li2CO3 and LiOH on the surface. LiOH can react with the electrolyte LiPF6 to produce HF to corrode the electrode; Li2CO3 will swell during high temperature storage, increase irreversible capacity and charge transfer resistance, and inhibit Li + Diffusion. To remove residual lithium, water washing or acid washing processes are widely used in actual production, followed by calcination to restore performance. However, water washing + calcination not only prolongs production time, but also makes it difficult for layered cathode materials to recover their initial performance after water washing and calcination, resulting in a decrease in performance.

[0003] In addition, the water content in the positive electrode material will react with the binder to form a colloidal substance, resulting in poor fluidity and leveling of the slurry, which is not conducive to the coating of the slurry and affects the processing performance. After the battery is manufactured, its capacity, internal resistance, cycle life, and rate capability will be affected. In addition to having a significant impact on the preparation of lithium battery slurry, excessive water content will cause the electrolyte to decompose into hydrofluoric acid. As a highly corrosive acid, hydrofluoric acid will cause serious damage to the positive and negative electrode materials and current collectors of lithium batteries, ultimately leading to battery safety issues. Therefore, removing residual lithium on the surface of the positive electrode material and reducing the water content in the positive electrode material are important research directions for improving the performance, safety and stability of lithium-ion batteries.

[0004] In view of this, the present disclosure is proposed.

[0005] Summary of the Invention

[0006] The purpose of the present disclosure is to provide a positive electrode material, a preparation method and an application thereof, and to reduce residual lithium on the surface of a ternary material.

[0007] The present disclosure is achieved as follows:

[0008] In a first aspect, the present disclosure provides a positive electrode material comprising a nickel-cobalt-manganese ternary material and a titanium dioxide coating layer coated on the nickel-cobalt-manganese ternary material, wherein polydimethylsiloxane is grafted onto the titanium dioxide on the surface of the coating layer.

[0009] In some embodiments, the mass of the titanium dioxide is 0.1 wt%-10 wt% of the mass of the nickel-cobalt-manganese ternary material.

[0010] In some embodiments, the mass ratio of the polydimethylsiloxane to the titanium dioxide is (0.01-1):(0.01-1).

[0011] In a second aspect, the present disclosure provides a method for preparing the positive electrode material described in any one of the aforementioned embodiments, mixing a nickel-cobalt-manganese ternary material coated with titanium dioxide with polydimethylsiloxane to obtain a second mixture, and irradiating the mixture with ultraviolet light to graft the polydimethylsiloxane onto the titanium dioxide.

[0012] In some embodiments, the titanium dioxide-coated nickel-cobalt-manganese ternary material is mixed with a second organic solvent to obtain a first solid-liquid mixture, which is then mixed with polydimethylsiloxane to obtain a second solid-liquid mixture, and then the second organic solvent is evaporated to obtain the second mixture.

[0013] In some embodiments, the solid-liquid ratio in the first solid-liquid mixture is (0.01-1)g:(0.1-1)L.

[0014] In some embodiments, the second organic solvent is at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol.

[0015] In some embodiments, the first solid-liquid mixture is subjected to ultrasonic treatment and then mixed with the polydimethylsiloxane.

[0016] In some embodiments, the polydimethylsiloxane and the titanium dioxide-coated ternary cathode material are mixed in a mass ratio of 1:10-1:100 to obtain the second solid-liquid mixture.

[0017] In some embodiments, the second solid-liquid mixture is placed at a temperature of 60° C. to 200° C. to evaporate the second organic solvent until the second organic solvent content is less than 0.1 wt %.

[0018] In some embodiments, the ultraviolet light has a wavelength of 200 nm to 600 nm.

[0019] In some embodiments, the ultraviolet irradiation time of the second mixture is 1 hour to 6 hours.

[0020] In some embodiments, the ultraviolet light irradiates the second mixture while stirring the mixture.

[0021] In some embodiments, the method further includes preparing a titanium dioxide coating layer: calcining a first mixture including the nickel-cobalt-manganese ternary material and a titanium source to obtain a titanium dioxide-coated nickel-cobalt-manganese ternary material.

[0022] In some embodiments, the mass of the titanium source in the first mixture is 0.1 wt % to 10 wt % of the mass of the nickel-cobalt-manganese ternary material.

[0023] In some embodiments, the titanium source is at least one of titanium powder, titanium isopropoxide, butyl titanate, titanium dioxide, titanium tetrachloride, titanium hydroxide, titanium nitrate, titanium sulfate, and titanium nitride.

[0024] In some embodiments, the solid component in the titanium source is a nano-scale powder.

[0025] In some embodiments, the nickel-cobalt-manganese ternary material is mixed with a first organic solvent, and then mixed with the titanium source, and then freeze-dried to obtain the first mixture.

[0026] In some embodiments, the nickel-cobalt-manganese ternary material is mixed with the first organic solvent at a solid-liquid ratio of (0.5-1) g:1L.

[0027] In some embodiments, the first organic solvent is at least one of petroleum ether, tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol.

[0028] In some embodiments, the temperature of the freeze-drying step is -70°C to -30°C, and the freeze-drying step is performed until the content of the first organic solvent is less than 1 wt%.

[0029] In some embodiments, the calcination temperature is 300-1000° C., and the calcination time is 0.5 h-8 h.

[0030] In a third aspect, the present disclosure provides a battery comprising the positive electrode material described in any one of the aforementioned embodiments or the positive electrode material obtained by the method described in any one of the aforementioned embodiments.

[0031] In a fourth aspect, the present disclosure provides an electrical device comprising the battery described in the aforementioned embodiment.

[0032] The present disclosure has the following beneficial effects:

[0033] The positive electrode material disclosed herein includes titanium dioxide coated on a ternary material, and polydimethylsiloxane is grafted onto the titanium dioxide to form a hydrophobic layer. On the one hand, the hydrophobic layer can physically isolate lithium oxide from reacting with water and carbon dioxide in the air. On the other hand, polydimethylsiloxane is grafted onto the titanium dioxide, and the two are connected by chemical bonds to form a more stable hydrophobic layer. The hydrophobic layer formed by polydimethylsiloxane grafted onto the titanium dioxide is more hydrophobic than that formed by directly modifying the ternary material with siloxane, and can also have more stable durability in long-term immersion in the electrolyte, preventing the reaction of HF acid in the electrolyte with titanium dioxide or the positive electrode material, thereby enhancing the chemical stability of the positive electrode material and the safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0035] FIG1 is a flow chart of the preparation of positive electrode materials;

[0036] Figure 2 shows the LiNi modified by polydimethylsiloxane grafted TiO2 coating obtained in Example 1. 0.8 Co 0.1 Mn 0.1 SEM image of O2 positive electrode material. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0038] An embodiment of the present disclosure provides a positive electrode material, including a nickel-cobalt-manganese ternary material and a titanium dioxide coating layer coated on the nickel-cobalt-manganese ternary material, wherein polydimethylsiloxane is grafted onto the titanium dioxide on the surface of the coating layer.

[0039] The positive electrode material in this embodiment includes titanium dioxide coated on a ternary material, and polydimethylsiloxane is grafted onto the titanium dioxide to form a hydrophobic layer. On the one hand, the hydrophobic layer can physically isolate the lithium oxide from reacting with water and carbon dioxide in the air. On the other hand, polydimethylsiloxane is grafted onto the titanium dioxide, and the two are connected by chemical bonds to form a more stable hydrophobic layer. The hydrophobic layer formed by polydimethylsiloxane grafted onto the titanium dioxide is more hydrophobic than the direct use of siloxane to modify the ternary material. It can also have more stable durability in long-term immersion in the electrolyte, preventing the reaction of HF acid in the electrolyte with titanium dioxide or the positive electrode material, thereby enhancing the chemical stability of the positive electrode material and the safety of the battery.

[0040] In some embodiments, the mass of the titanium dioxide is 0.1wt%-10wt% of the mass of the nickel-cobalt-manganese ternary material, specifically 0.1wt%, 0.5wt%, 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt% or any value between 0.1wt% and 10wt%. If the amount of titanium dioxide is too small, the isolation and hydrophobic effects are not good, but if the amount of titanium dioxide is too much, the capacity of the positive electrode material will be greatly reduced. Therefore, the content of titanium dioxide needs to be within a reasonable range.

[0041] In some embodiments, the molar ratio of the polydimethylsiloxane to the molar ratio of the titanium dioxide is (0.01-1):(0.01-1), specifically 0.01:0.01, 0.01:0.1, 0.01:1, 0.1:0.01, 1:0.01, or any value between (0.01-1):(0.01-1). If the amount of polydimethylsiloxane used is too small, the surface of the positive electrode material cannot be completely covered, but if the amount of polydimethylsiloxane used is too large, some of the polydimethylsiloxane will not be able to form bonds with titanium dioxide or other elements, causing the polydimethylsiloxane to adhere to the surface of the positive electrode material through intermolecular forces, resulting in low binding force, which is not conducive to improving the cycle performance of the positive electrode material.

[0042] The present disclosure provides a method for preparing the positive electrode material described in any one of the aforementioned embodiments. As shown in Figure 1, a nickel-cobalt-manganese ternary material coated with titanium dioxide is mixed with polydimethylsiloxane to obtain a second mixture, and the mixture is irradiated with ultraviolet light to graft the polydimethylsiloxane onto the titanium dioxide.

[0043] In this embodiment, a small amount of water molecules are present on the surface of titanium dioxide. Ultraviolet light is used to break the hydroxyl groups in the water molecules on the surface of titanium dioxide. At the same time, under ultraviolet light, electron-hole pairs are generated on the surface of titanium dioxide, which excite the hydroxyl groups and water molecules on the surface. These active groups partially cut the surrounding polydimethylsiloxane chains, so that the cut polydimethylsiloxane chains form Ti-O-Si chemical bonds with the titanium in the titanium dioxide. Polydimethylsiloxane is grafted to the surface by photocatalysis on the surface of titanium dioxide, so that it has superhydrophobic properties. In addition, the broken polydimethylsiloxane chains after cutting can form Li-O-Si chemical bonds with the lithium in lithium oxide, which plays a role in pulling out lithium, reducing the residual lithium on the surface of the particles, and thereby reducing the residual alkali of the positive electrode material.

[0044] In some embodiments, the titanium dioxide-coated nickel-cobalt-manganese ternary material is mixed with a second organic solvent to obtain a first solid-liquid mixture, which is then mixed with polydimethylsiloxane to obtain a second solid-liquid mixture, and then the second organic solvent is evaporated to obtain the second mixture.

[0045] In this embodiment, the nickel-cobalt-manganese ternary material coated with titanium dioxide cannot be mixed evenly with polydimethylsiloxane by directly mixing. The organic solvent acts as a co-solvent, and the nickel-cobalt-manganese ternary material coated with titanium dioxide and polydimethylsiloxane are evenly mixed through the organic solvent. However, the presence of the co-solvent will dilute the concentration of titanium dioxide and polydimethylsiloxane, increasing the difficulty of grafting. Therefore, before grafting polydimethylsiloxane onto titanium dioxide, the organic solvent is first removed.

[0046] In some embodiments, the solid-liquid ratio of the first solid-liquid mixture is (0.01-1) g:(0.1-1) L, specifically 0.01 g / L, 0.1 g / L, 1 g / L, 10 g / L, or any value between (0.01-1) g:(0.1-1) L. Since polydimethylsiloxane has good hydrophobicity, while the titanium dioxide-coated nickel-cobalt-manganese ternary material has a certain degree of hydrophilicity, the two have significant differences in properties. Therefore, when the two are mixed, a relatively large amount of cosolvent needs to be added. However, if there is too much cosolvent, the energy consumption for removing the cosolvent later is too high, so the amount of cosolvent used needs to be within a reasonable range.

[0047] In some embodiments, the second organic solvent is at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol.

[0048] In some embodiments, the first solid-liquid mixture is ultrasonically treated and then mixed with the polydimethylsiloxane. In order to allow the titanium dioxide-coated nickel-cobalt-manganese ternary material to be first evenly dispersed in the second organic solvent and then better mixed with the polydimethylsiloxane, the first solid-liquid mixture is first ultrasonically treated. In some embodiments, the ultrasonic temperature is room temperature, the time is 20 minutes, and the frequency is 100 Hz.

[0049] In some embodiments, the polydimethylsiloxane is mixed with the ternary positive electrode material in the first solid-liquid mixture in a mass ratio of 1:10-1:100 to obtain the second solid-liquid mixture. Specifically, the mass ratio of polydimethylsiloxane to the ternary positive electrode material in the first solid-liquid mixture is 1:10, 1:20, 1:30, 1:50, 1:100 or any value between 1:10-1:100.

[0050] In some embodiments, the second solid-liquid mixture is placed at a temperature of 60°C-200°C to evaporate the second organic solvent until the second organic solvent content is less than 0.1 wt%. Specifically, the evaporation temperature can be 60°C, 80°C, 100°C, 150°C, 200°C or any value between 60°C and 200°C.

[0051] In this embodiment, the evaporation temperature is related to the boiling point of the second organic solvent. If the boiling point is high, a relatively high evaporation temperature can be selected. If the boiling point is low, a relatively low evaporation temperature can also be selected. Residual second organic solvent may affect the normal film formation reaction of the electrolyte solvent during the formation stage, seriously affecting battery performance. Therefore, the second organic solvent should be removed as completely as possible.

[0052] In some embodiments, the wavelength of the ultraviolet light is 200 nm-400 nm, specifically 200 nm, 300 nm, 400 nm or any value between 200 nm and 400 nm.

[0053] In some embodiments, the ultraviolet irradiation time of the second mixture is 1h-6h, specifically 1h, 2h, 3h, 4h, 5h, 6h or any value between 1h-6h. Prolonging the ultraviolet irradiation time is beneficial to improving the grafting rate of titanium dioxide on the particle surface.

[0054] In some embodiments, the ultraviolet ray irradiates the second mixture while stirring the mixture, and the stirring mainly improves the uniformity of the reaction system.

[0055] In some embodiments, the method further includes preparing a titanium dioxide coating layer: calcining a first mixture including the nickel-cobalt-manganese ternary material and a titanium source to obtain a titanium dioxide-coated nickel-cobalt-manganese ternary material.

[0056] During the calcination process, on the one hand, the titanium source is oxidized into titanium dioxide, while at the same time improving the bonding strength between titanium dioxide and the nickel-cobalt-manganese ternary material; on the other hand, titanium dioxide can also react with lithium carbonate to reduce the residual alkali on the surface of the positive-valent material.

[0057] In some embodiments, the mass of the titanium source in the first mixture is 0.1wt%-10wt% of the mass of the nickel-cobalt-manganese ternary material, specifically 0.1wt%, 0.5wt%, 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt% or any value between 0.1wt% and 10wt%.

[0058] In some embodiments, the titanium source is at least one of titanium powder, titanium isopropoxide, butyl titanate, titanium dioxide, titanium tetrachloride, titanium hydroxide, titanium nitrate, titanium sulfate, and titanium nitride.

[0059] In some embodiments, the solid component in the titanium source is a nano-scale powder, which is conducive to uniform coating of the solid titanium source on the surface of the nickel-cobalt-manganese ternary material, thereby improving the uniformity of titanium dioxide coated on the surface of the nickel-cobalt-manganese ternary material.

[0060] In some embodiments, the nickel-cobalt-manganese ternary material is mixed with a first organic solvent, and then mixed with the titanium source, and then freeze-dried to obtain the first mixture.

[0061] In some embodiments of freeze-drying, the nickel-cobalt-manganese ternary material is mixed with the first organic solvent at a solid-liquid ratio of (0.5-1) g:1 L, specifically 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L, 1 g / L, or any value between (0.5-1) g:1 L. In this embodiment, since both the ternary material and titanium dioxide have a certain degree of hydrophilicity, the first organic solvent only serves to provide a liquid phase environment that facilitates uniform dispersion of the solids. Compared with the second organic solvent, the first organic solvent has a wider range of choices and can be used in a relatively smaller amount.

[0062] In some embodiments, the first organic solvent is at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol.

[0063] In some embodiments, the freeze-drying step is performed at a temperature of -70°C to -30°C until the content of the first organic solvent is less than 1 wt %. The freeze-drying temperature mainly affects the drying speed. In some embodiments, the calcination temperature is 300°C to 1000°C, specifically 300°C, 500°C, 700°C, 900°C, 1000°C or any value between 300°C and 1000°C; the calcination time is 0.5h to 8h, specifically 0.5h, 1h, 2h, 4h, 6h, 8h or any value between 0.5h and 8h.

[0064] The selection of calcination conditions is crucial for the formation of titanium dioxide coating. When the calcination temperature is too high and the time is too long, it will affect the crystal structure of the nickel-cobalt-manganese lithium battery positive electrode material itself, destroy the electrochemical activity of the main material, and cause the electrochemical performance of the ternary positive electrode material to decline; when the calcination temperature is too low and the time is too short, the titanium source is difficult to effectively pyrolyze, or the formed coating has low crystallinity, making it difficult to form an effective coating.

[0065] In a third aspect, the present disclosure provides a battery comprising the positive electrode material described in any one of the aforementioned embodiments or the positive electrode material obtained by the method described in any one of the aforementioned embodiments.

[0066] In a fourth aspect, the present disclosure provides an electrical device comprising the battery described in the aforementioned embodiment.

[0067] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0068] Example 1:

[0069] This embodiment provides a method for preparing a positive electrode material, comprising the following steps:

[0070] Take LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material is dispersed in ethanol, LiNi 0.8 Co 0.1 Mn 0.1 The solid-liquid ratio of the O2 cathode material to ethanol was 0.5g:0.1L, and the mixture was stirred with a magnetic stirrer for 1 hour to uniformly disperse the solid phase. Subsequently, titanium isopropoxide was added to the ethanol solution at a mass ratio of 25:1 between the ternary cathode material and titanium isopropoxide. After magnetic stirring for 1 hour to uniformly disperse the mixture in the ethanol solution, the mixture was freeze-dried until the ethanol content was less than 1wt%. The dried mixture was then placed in an oxygen atmosphere and calcined at 700°C for 4 hours to obtain a titanium dioxide-coated ternary cathode material.

[0071] Take the TiO2 coated LiNi obtained in the above steps 0.8Co 0.1 Mn 0.1 The O2 positive electrode material and tetrahydrofuran were uniformly mixed in a mass volume ratio of 1g:0.1L, and ultrasonic treatment was performed to make the mixture uniform. Then, polydimethylsiloxane was mixed in a mass ratio of 50:1 between the positive electrode material and polydimethylsiloxane. The mixture was uniformly mixed by sufficient stirring. After that, tetrahydrofuran was evaporated at 70°C until the tetrahydrofuran content was less than 0.1wt%. The mixture was irradiated with a 300nm wavelength ultraviolet lamp and stirred for 2h to obtain polydimethylsiloxane-grafted TiO2-coated modified LiNi. 0.8 Co 0.1 Mn 0.1 O2 positive electrode material, SEM image is shown in Figure 2.

[0072] The TiO2 prepared above was coated on the modified LiNi 0.8 Co 0.1 Mn 0.1 The O2 positive electrode material, conductive carbon black, and binder PVDF were mixed in a ratio of 97.2:1.4:1.4, and a small amount of N-methylpyrrolidone was added to fully grind and mix to form a paste, which was then coated on an aluminum foil substrate as a test electrode.

[0073] Example 2:

[0074] This embodiment provides a method for preparing a positive electrode material, which differs from Example 1 only in that, during the preparation of the titanium dioxide-coated ternary positive electrode material, titanium isopropoxide is introduced at a mass ratio of 50:3 between the ternary positive electrode material and titanium isopropoxide.

[0075] Example 3:

[0076] This embodiment provides a method for preparing a positive electrode material, which differs from Example 1 only in that, during the preparation of the titanium dioxide-coated ternary positive electrode material, titanium isopropoxide is introduced at a mass ratio of 100:1 between the ternary positive electrode material and titanium isopropoxide.

[0077] Example 4:

[0078] This embodiment provides a method for preparing a positive electrode material, which differs from Example 1 only in that, during the grafting process of polydimethylsiloxane, polydimethylsiloxane is introduced and mixed into the titanium dioxide-coated ternary positive electrode material at a ratio of 25:1.

[0079] Example 5:

[0080] This embodiment provides a method for preparing a positive electrode material, which differs from Example 1 only in that, during the grafting process of polydimethylsiloxane, polydimethylsiloxane is introduced and mixed therein at a ratio of 100:1 between the titanium dioxide-coated ternary positive electrode material and the polydimethylsiloxane.

[0081] Example 6:

[0082] This embodiment provides a method for preparing a positive electrode material, which differs from Embodiment 1 only in that ultraviolet irradiation is performed for 6 hours.

[0083] Example 7:

[0084] This embodiment provides a method for preparing a positive electrode material, which is different from Example 1 only in that the ultraviolet irradiation time is 0.5 h.

[0085] Comparative Example 1:

[0086] This comparative example provides a method for preparing a positive electrode material, which differs from Example 1 only in that titanium dioxide is not coated:

[0087] Take LiNi 0.8 Co 0.1 Mn 0.1 O2 and tetrahydrofuran were evenly mixed in a mass volume ratio of 0.5g:0.1L, and ultrasonic treatment was used to make them evenly mixed. Then, polydimethylsiloxane was mixed in a mass ratio of 50:1 between the positive electrode material and polydimethylsiloxane. The mixture was evenly mixed by stirring, and then tetrahydrofuran was evaporated at 70°C to obtain polydimethylsiloxane-coated modified LiNi. 0.8 Co 0.1 Mn 0.1 O2 positive electrode material.

[0088] The polydimethylsiloxane-coated LiNi 0.8 Co 0.1 Mn 0.1 The O2 positive electrode material, conductive carbon black, and binder PVDF were mixed in a ratio of 97.2:1.4:1.4, and a small amount of N-methylpyrrolidone was added to fully grind and mix to form a paste, which was then coated on an aluminum foil substrate as a test electrode.

[0089] Comparative Example 2:

[0090] This comparative example provides a method for preparing a positive electrode material, which differs from Example 1 only in that polydimethylsiloxane is not grafted onto titanium dioxide:

[0091] Take LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material is dispersed in ethanol, LiNi 0.8 Co 0.1 Mn 0.1The solid-liquid ratio of the O2 cathode material to ethanol was 0.5g:0.1L, and the mixture was stirred with a magnetic stirrer for 1 hour to uniformly disperse the solid phase. Subsequently, titanium isopropoxide was added to the ethanol solution at a mass ratio of 25:1 between the ternary cathode material and titanium isopropoxide. After magnetic stirring for 1 hour to uniformly disperse the mixture in the ethanol solution, the mixture was freeze-dried until the ethanol content was less than 1wt%. The dried mixture was then placed in an oxygen atmosphere and calcined at 700°C for 4 hours to obtain a titanium dioxide-coated ternary cathode material.

[0092] The titanium dioxide-coated ternary positive electrode material was directly mixed with the conductive agent conductive carbon black and the binder PVDF in a ratio of 97.2:1.4:1.4, and a small amount of N-methylpyrrolidone was added to fully grind and mix to form a paste, which was then coated on an aluminum foil substrate as a test electrode.

[0093] Comparative Example 3:

[0094] This comparative example provides a method for preparing a positive electrode material, which differs from Example 1 only in that no ultraviolet irradiation is performed:

[0095] Take LiNi 0.8 Co 0.1 Mn 0.1 O2 cathode material is dispersed in ethanol, LiNi 0.8 Co 0.1 Mn 0.1 The solid-liquid ratio of the O2 cathode material to ethanol was 0.5g:0.1L, and the mixture was stirred with a magnetic stirrer for 1 hour to uniformly disperse the solid phase. Subsequently, titanium isopropoxide was added to the ethanol solution at a mass ratio of 25:1 between the ternary cathode material and titanium isopropoxide. After magnetic stirring for 1 hour to uniformly disperse the mixture in the ethanol solution, the mixture was freeze-dried until the ethanol content was less than 1wt%. The dried mixture was then placed in an oxygen atmosphere and calcined at 700°C for 4 hours to obtain a titanium dioxide-coated ternary cathode material.

[0096] Take the TiO2 coated LiNi obtained in the above steps 0.8 Co 0.1 Mn 0.1 The O2 positive electrode material and tetrahydrofuran are evenly mixed in a mass volume ratio of 1g:0.1L, and ultrasonic treatment is performed to make the mixture uniform. Then, polydimethylsiloxane is mixed in a mass ratio of 50:1 between the positive electrode material and polydimethylsiloxane, and the mixture is evenly mixed by sufficient stirring. After that, the tetrahydrofuran is evaporated at 70°C until the tetrahydrofuran content is less than 0.1wt%, and LiNi coated with polydimethylsiloxane and TiO2 is obtained. 0.8 Co 0.1 Mn 0.1 O2 positive electrode material.

[0097] The positive electrode material prepared above was mixed with the conductive agent conductive carbon black and the binder PVDF in a ratio of 97.2:1.4:1.4, and a small amount of N-methylpyrrolidone was added to form a paste, which was then coated on an aluminum foil substrate as a test electrode.

[0098] Performance testing method: Assembled button cells were tested with a voltage range of 3.0-4.3V and a test temperature of 25°C. The actual battery capacity was tested at 0.1C, the rate performance of the cathode material was tested at 0.1C, and the cycle stability of the cathode material was tested at 0.1C. The test results are shown in Table 1.

[0099] Water contact angle test method: The positive electrode material slurry prepared according to the requirements was coated on a glass slide and dried in a vacuum oven at 40°C for 24 hours. The static water contact angle was then measured. The test results are shown in Table 1.

[0100] Table 1 Physical properties of the products prepared in Examples 1-4 and Comparative Examples 1-3 and corresponding lithium ion battery electrical performance data

[0101] As can be seen from Table 1:

[0102] (1) It can be seen from Examples 1-7 and Comparative Examples 1-3 that the high nickel ternary positive electrode material prepared by coating grafted polydimethylsiloxane titanium dioxide in the present invention has excellent hydrophobicity, low surface residual alkali content, and excellent initial charge and discharge specific capacity and cycle performance;

[0103] (2) As shown in Examples 1-7, increasing the content of titanium oxide and siloxane, as well as increasing the ultraviolet irradiation time, is beneficial to increasing the hydrophobicity of the material, reducing the residual alkali on the surface, increasing the initial charge and discharge specific capacity, and improving the cycle performance;

[0104] (3) Comparative Examples 1-3 show that after removing the doping of silicon dioxide in the preparation process, the residual alkali content on the surface of the material will be greatly increased; removing polydimethylsiloxane will cause the hydrophobicity of the material to be greatly reduced, and at the same time will cause the residual alkali content on the surface of the material to increase, and the cycle performance will deteriorate; after not undergoing the ultraviolet irradiation step, titanium dioxide is mixed with the positive electrode material by physical doping, resulting in its lack of durability and reduced battery cycle performance. Industrial Applicability

[0105] The positive electrode material disclosed herein includes titanium dioxide coated on a ternary material, and polydimethylsiloxane is grafted onto the titanium dioxide to form a hydrophobic layer. On the one hand, the hydrophobic layer can physically isolate lithium oxide from reacting with water and carbon dioxide in the air. On the other hand, polydimethylsiloxane is grafted onto the titanium dioxide, and the two are connected by chemical bonds to form a more stable hydrophobic layer. The hydrophobic layer formed by polydimethylsiloxane grafted onto the titanium dioxide is more hydrophobic than that formed by directly modifying the ternary material with siloxane, and can also have more stable durability in long-term immersion in the electrolyte, preventing the reaction of HF acid in the electrolyte with titanium dioxide or the positive electrode material, enhancing the chemical stability of the positive electrode material and the safety of the battery, and having industrial applicability.

Claims

1. A positive electrode material, characterized in that: The invention comprises a nickel-cobalt-manganese ternary material and a titanium dioxide coating layer coated on the nickel-cobalt-manganese ternary material, and polydimethylsiloxane is grafted on the titanium dioxide on the surface of the coating layer.

2. The positive electrode material according to claim 1, characterized in that The mass of the titanium dioxide is 0.1wt%-10wt% of the mass of the nickel-cobalt-manganese ternary material.

3. The positive electrode material according to claim 1 or 2, characterized in that The molar ratio of the polydimethylsiloxane to the titanium dioxide is (0.01-1):(0.01-1).

4. A method for preparing the positive electrode material according to any one of claims 1 to 3, characterized in that: The titanium dioxide-coated nickel-cobalt-manganese ternary material is mixed with polydimethylsiloxane to obtain a second mixture, and the mixture is irradiated with ultraviolet rays to graft the polydimethylsiloxane onto the titanium dioxide.

5. The method for preparing the positive electrode material according to claim 4, characterized in that: The titanium dioxide-coated nickel-cobalt-manganese ternary material is mixed with a second organic solvent to obtain a first solid-liquid mixture, which is then mixed with polydimethylsiloxane to obtain a second solid-liquid mixture, and then the second organic solvent is evaporated to obtain the second mixture.

6. The method for preparing the positive electrode material according to claim 5, characterized in that: The solid-liquid ratio in the first solid-liquid mixture is (0.01-1)g:(0.1-1)L.

7. The method for preparing the positive electrode material according to claim 5 or 6, characterized in that: The second organic solvent is at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol.

8. The method for preparing the positive electrode material according to any one of claims 5 to 7, characterized in that: The first solid-liquid mixture is subjected to ultrasonic treatment and then mixed with the polydimethylsiloxane.

9. The method for preparing a positive electrode material according to any one of claims 5 to 8, characterized in that: The first solid-liquid mixture is mixed with polydimethylsiloxane at a volume ratio of 1:1-1:50 to obtain the second solid-liquid mixture.

10. The method for preparing a positive electrode material according to any one of claims 5 to 9, characterized in that: The second solid-liquid mixture is placed at a temperature of 60° C. to 200° C. to evaporate the second organic solvent until the content of the second organic solvent is less than 0.1 wt %.

11. The method for preparing a positive electrode material according to any one of claims 4 to 10, characterized in that: The wavelength of the ultraviolet rays is 200nm-400nm.

12. The method for preparing a positive electrode material according to any one of claims 4 to 11, characterized in that: The ultraviolet irradiation time of the second mixture is 1h-6h.

13. The method for preparing a positive electrode material according to any one of claims 4 to 12, characterized in that: The ultraviolet rays irradiate the second mixture while stirring the mixture.

14. The method for preparing a positive electrode material according to any one of claims 4 to 13, characterized in that: The method also includes the preparation of a titanium dioxide coating layer: calcining a first mixture including the nickel-cobalt-manganese ternary material and a titanium source to obtain a titanium dioxide-coated nickel-cobalt-manganese ternary material.

15. The method for preparing the positive electrode material according to claim 14, characterized in that: The mass of the titanium source in the first mixture is 0.1wt%-10wt% of the mass of the nickel-cobalt-manganese ternary material.

16. The method for preparing the positive electrode material according to claim 14 or 15, characterized in that: The titanium source is at least one of titanium powder, titanium isopropoxide, butyl titanate, titanium dioxide, titanium tetrachloride, titanium hydroxide, titanium nitrate, titanium sulfate and titanium nitride.

17. The method for preparing the positive electrode material according to claim 16, characterized in that: The solid component in the titanium source is nanometer-scale powder.

18. The method for preparing a positive electrode material according to any one of claims 14 to 17, characterized in that: The nickel-cobalt-manganese ternary material is mixed with the first organic solvent and then mixed with the titanium source, followed by freeze-drying to obtain the first mixture.

19. The method for preparing the positive electrode material according to claim 18, characterized in that: The nickel-cobalt-manganese ternary material is mixed with the first organic solvent at a solid-liquid ratio of (0.5-1) g:1L.

20. The method for preparing a positive electrode material according to claim 18 or 19, characterized in that: The first organic solvent is at least one of tetrahydrofuran, n-hexane, toluene, isopropanol, acetone, n-hexane, methanol and ethanol.

21. The method for preparing a positive electrode material according to any one of claims 18 to 20, characterized in that: The temperature of the freeze-drying step is -70°C to -30°C, and the freeze-drying step is performed until the content of the first organic solvent is less than 1 wt%.

22. The method for preparing a positive electrode material according to any one of claims 14 to 21, characterized in that: The calcination temperature is 300-1000°C, and the calcination time is 0.5h-8h.

23. A battery, characterized in that: The invention comprises the positive electrode material according to any one of claims 1 to 3 or the positive electrode material obtained by the method according to any one of claims 4 to 22.

24. An electrical equipment, characterized in that: Comprising the battery of claim 23.

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