Nano-hydroxyl cobalt oxide, and preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a nano-hydroxyl cobalt oxide as well as a preparation method and application thereof. The method uses cobalt nitrate hexahydrate as raw material, cooperates with a double-amine system of n-butylamine and n-dodecylamine to limit the growth of nanosheets, controls the ultrathin sheet structure of the nano-hydroxyl cobalt oxide through mild step-by-step sodium hypochlorite oxidation and limited regrowth, further utilizes surface silane grafting and two-stage poly(2-oxazoline) brush layer to realize accurate regulation of the electrode-electrolyte interface of the material, and effectively reduces the interface impedance. The obtained material has high specific surface area, low surface resistance, excellent rate performance and long cycle stability. The application innovatively combines morphology control and interface engineering, improves the electrochemical performance of the material, and provides a new technical route for the research and industrialization of high-performance lithium battery electrode materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a kind of nanometer cobalt oxyhydroxide and its preparation method and application. BACKGROUND

[0002] With the rapid development of electric vehicles, energy storage systems and portable electronic devices, the demand for high-performance lithium ion batteries is increasingly urgent. As an important transition metal compound, cobalt oxyhydroxide (CoOOH) has attracted widespread attention in the field of lithium ion battery anode materials due to its high theoretical specific capacity, abundant resources and environmental friendliness. However, traditional CoOOH materials face key technical bottlenecks such as limited electron / ion transport and poor rate performance in practical applications.

[0003] In the prior art, the preparation of CoOOH material mainly adopts direct chemical oxidation or electrochemical in-situ method, and most of the nanosheets / nanosheet cluster structures are prepared. Although it has been reported that sodium hypochlorite can be used to mildly oxidize β-Co(OH)2 under alkaline conditions to β-CoOOH, and the precursor morphology and size can be relatively well maintained, but this mild external oxidation system still has significant limitations. First, the traditional preparation method is difficult to accurately control the thickness of the nanosheet, and the prepared CoOOH material usually has a large thickness, which prolongs the lithium ion diffusion path and limits the rate performance of the material. Secondly, the conventional preparation process lacks effective means of morphology control, and cannot simultaneously achieve the synergistic optimization of ultra-thin thickness and high specific surface area, which affects the active site density and electrochemical reaction kinetics.

[0004] More importantly, the existing CoOOH material generally has a high interface impedance. During the operation of lithium ion batteries, the interface resistance between the electrode material and the electrolyte directly affects the charge transfer efficiency and battery performance. The traditional CoOOH material lacks effective interface engineering design on the surface, and the electrode-electrolyte interface microenvironment is not well regulated, resulting in high interface resistance, which seriously restricts the rate performance and cycle stability of the material. Especially under high-rate charge and discharge conditions, the interface polarization is intensified, and the electrochemical performance is deteriorated sharply.

[0005] In the aspect of interface engineering, the prior art mainly adopts simple surface coating or doping modification, and lacks precise interface structure design. These traditional modification methods often lead to a decrease in active material loading, or the modification layer is not firmly combined with the matrix, and is easily detached in the cycle process, affecting the long-term stability of the battery. Especially, there is a lack of effective means to precisely regulate the electrolyte microenvironment through surface functionalization molecules, which cannot fundamentally solve the problem of high interface impedance.

[0006] In summary, the prior art has significant technical gaps in the accurate control of the thickness of CoOOH materials and the optimization of interface impedance, and new preparation methods and technical routes are urgently needed to meet the strict requirements of high-performance lithium-ion batteries for electrode materials. SUMMARY

[0007] Therefore, the present application aims to provide a nano-hydroxyl cobalt oxide, a preparation method and application thereof, so as to solve the problems of thick CoOOH material, high interface impedance, poor rate performance and short cycle life of lithium batteries.

[0008] To achieve the above purpose, the present application provides a preparation method of nano-hydroxyl cobalt oxide, comprising the following steps:

[0009] S1: stirring cobalt nitrate hexahydrate, urea, n-butylamine, n-dodecylamine and deionized water at room temperature for 25-35 min, then heating to 60-70 DEG C and keeping stirring for 60-120 min, cooling to room temperature, to obtain a uniform suspension;

[0010] S2: adding the uniform suspension obtained in step S1 into sodium hydroxide aqueous solution, stirring for 12-20 min, then keeping stirring at 40-50 DEG C for 40-60 min, centrifuging, washing with water, and dispersing in sodium hydroxide aqueous solution to obtain nano-Co(OH)2 precursor slurry;

[0011] S3: under ice bath condition, adding alkaline sodium hypochlorite oxidizing solution dropwise into the nano-Co(OH)2 precursor slurry obtained in step S2, heating to 12-18 DEG C and stirring for 20-30 min, centrifuging, and washing to obtain nano-CoOOH precursor A;

[0012] S4: adding the nano-CoOOH precursor A obtained in step S3 into deionized water, then adding n-butylamine, n-dodecylamine and urea, stirring at 45-55 DEG C for 30-45 min, cooling to room temperature, centrifuging, washing with water, and dispersing in sodium hydroxide aqueous solution, then adding alkaline sodium hypochlorite oxidizing solution, stirring for 25-35 min, centrifuging, and washing to obtain nano-CoOOH precursor B;

[0013] S5: adding the nano-CoOOH precursor B obtained in step S4 into anhydrous ethanol, then adding 3-chloropropyltrimethoxysilane and deionized water, reacting at 68-75 DEG C under nitrogen protection for 40-70 min, centrifuging, vacuum drying, dispersing in N,N-dimethylformamide, adding sodium p-toluenesulfonate, reacting at 80-90 DEG C under nitrogen protection for 6-10 h, centrifuging, washing with water, and vacuum drying to obtain nano-CoOOH precursor containing initiation sites;

[0014] S6: adding the CoOOH precursor with initiating site obtained in step S5 and 2-methyl-2-oxazoline into anhydrous acetonitrile, reacting at 78-82°C for 8-12h under nitrogen atmosphere, then adding 2-nonyl-2-oxazoline, continuing to react at 78-82°C for 8-12h, centrifuging, washing, and vacuum drying to obtain nanometer hydroxyl cobalt oxide.

[0015] Preferably, the amount of urea added in step S1 is 20-30g, the amount of n-butylamine added is 6-10g, the amount of n-dodecylamine added is 3-6g, and the amount of deionized water added is 350-450mL, based on 16-20g of cobalt nitrate hexahydrate.

[0016] Preferably, the concentration of the aqueous sodium hydroxide solution is 0.3g / mL.

[0017] Preferably, the first amount of aqueous sodium hydroxide solution added in step S2 is 40-60mL, and the second amount of aqueous sodium hydroxide solution added is 40-60mL, based on 16-20g of cobalt nitrate hexahydrate.

[0018] Preferably, the basic sodium hypochlorite oxidizing solution is prepared from sodium hypochlorite, sodium hydroxide and deionized water, and the amount ratio of the sodium hypochlorite, sodium hydroxide and deionized water is 24-35g:12-18g:250mL.

[0019] Preferably, the amount of basic sodium hypochlorite oxidizing solution added in step S3 is 160-230mL, based on 16-20g of cobalt nitrate hexahydrate.

[0020] Preferably, the amount of deionized water added in step S4 is 280-350mL, the amount of n-butylamine added is 3-5g, the amount of n-dodecylamine added is 1.5-3g, the amount of urea added is 12-18g, the amount of aqueous sodium hydroxide solution added is 40-60mL, and the amount of basic sodium hypochlorite oxidizing solution added is 20-30mL, based on 16-20g of cobalt nitrate hexahydrate.

[0021] Preferably, the amount of anhydrous ethanol added in step S5 is 130-180mL, the amount of 3-chloropropyltrimethoxysilane added is 2-4g, the amount of deionized water added is 0.8-1.5mL, the amount of N,N-dimethylformamide added is 140-180mL, and the amount of sodium p-toluenesulfonate added is 4-6g, based on 16-20g of cobalt nitrate hexahydrate.

[0022] Preferably, the amount of 2-methyl-2-oxazoline added in step S6 is 6-10g, the amount of 2-nonyl-2-oxazoline added is 6-10g, and the amount of anhydrous acetonitrile added is 100-140mL, based on 16-20g of cobalt nitrate hexahydrate.

[0023] Further, the application also provides a nano cobalt oxyhydroxide obtained by the above-mentioned preparation method of the nano cobalt oxyhydroxide.

[0024] The application realizes the significant improvement of the nano cobalt oxyhydroxide material in thickness control, interface engineering and electrochemical performance through the integrated technical route of the dual-amine synergistic limited growth, mild oxidation and limited re-growth reciprocating treatment, surface silane grafting and two-stage polymeric brush layer construction.

[0025] Firstly, the technical advantage of the dual-amine synergistic limited mechanism lies in realizing the accurate regulation of the thickness of the nanosheet. The n-butylamine limits the layer-by-layer epitaxial growth through the coordination of the amino group and Co 2+ , and the n-dodecylamine uses the long-chain hydrophobic end to cap the edge of the sheet layer, and both of them synergistically regulate the "hydrolysis-condensation-layer-by-layer epitaxial growth" process, so that the thickness of the prepared nano cobalt oxyhydroxide is reduced to the ultra-thin range of 3-5 nm. This thickness control technology directly shortens the diffusion path of lithium ions, improves the specific surface area and active site density, and fundamentally improves the rate performance and first cycle reversibility of the material.

[0026] Secondly, the innovation of the mild oxidation of alkaline sodium hypochlorite and the limited re-growth-re-oxidation reciprocating treatment technology lies in introducing controllable structural defects while maintaining the integrity of the layer lattice. This mild step-by-step oxidation avoids the structural damage that may be caused by one-time strong oxidation, and through the reciprocating treatment, a proper amount of hydroxyl vacancies and controllable mismatches are introduced between the layers, forming active channels that are beneficial to ion / electron transmission. This technical feature significantly reduces the charge transfer resistance and improves the capacity performance under high rate conditions.

[0027] Thirdly, the surface silane grafting technology constructs controllable initiation sites through 3-chloropropyltrimethoxysilane, and after being activated by p-toluenesulfonate, it provides uniform anchoring points for subsequent polymerization reactions. This surface functionalization strategy ensures the strong bonding force between the polymer brush layer and the substrate, avoids the problem of easy detachment of the modified layer in traditional surface modification, and improves the stability of the interface structure.

[0028] Fourthly, the two-stage poly(2-oxazoline) brush layer construction technology realizes the accurate regulation of the electrode-electrolyte microenvironment. First, 2-methyl-2-oxazoline is polymerized to form a hydrophilic inner layer, which provides a good lithium ion transmission channel; and then 2-nonyl-2-oxazoline is polymerized to form a hydrophobic outer layer, which acts as a selective barrier. This hydrophilic-hydrophobic diblock structure optimizes the interface stability on the basis of ensuring the ion transmission efficiency, significantly reduces the interface resistance, and inhibits the occurrence of side reactions.

[0029] Most importantly, the application, by means of integrated coupling design of process time sequence, while maintaining the lattice layer characteristics and nanosheet ultrathin property, constructs a low-impedance and anti-attenuation interface structure, so that the material can still maintain a reversible capacity of more than 400 mAh / g under 10C high rate, and the capacity retention rate reaches more than 80% after 1000 cycles under 1C condition, effectively balancing the high rate performance and long cycle stability, and providing important technical support for the industrial application of high-performance lithium ion battery electrode materials. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below.

[0031] Figure 1 The X-ray diffraction spectrum of the nanometer cobalt oxyhydroxide in the embodiment 2 of the application;

[0032] Figure 2 The infrared spectrum of the nanometer CoOOH precursor B and the nanometer cobalt oxyhydroxide in the embodiment 2 of the application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the application more clear and obvious, the application will be further described in detail below in combination with specific embodiments.

[0034] Embodiment 1:

[0035] (1) 350 mL of deionized water, 16 g of cobalt nitrate hexahydrate and 20 g of urea were sequentially added into a 1000 mL beaker, and after stirring and dissolving, 6 g of n-butylamine and 3 g of n-dodecylamine were added, and after stirring at room temperature for 25 min, the temperature was increased to 60℃ and kept stirring for 60 min, and then cooled to room temperature to obtain a uniform suspension;

[0036] (2) The uniform suspension obtained in step (1) was added into 40 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL), stirred for 12 min, and then kept stirring at 40℃ for 40 min, and then centrifuged and washed with water for 3 times, and then dispersed in 40 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL) to obtain a nanometer Co(OH)2 precursor slurry;

[0037] (3) 24 g of sodium hypochlorite and 12 g of sodium hydroxide were dissolved in 250 mL of deionized water to obtain an alkaline sodium hypochlorite oxidation solution;

[0038] (4) Under ice bath condition, 160 mL of the alkaline sodium hypochlorite oxidation solution was added dropwise into the nanometer Co(OH)2 precursor slurry obtained in step (2), and stirred at 12℃ for 20 min, and then centrifuged and washed with anhydrous ethanol for 2 times to obtain a nanometer CoOOH precursor A;

[0039] (5) The nano CoOOH precursor A obtained in step (4) is added into 280 mL of deionized water, 3 g of n-butylamine, 1.5 g of n-dodecylamine, and 12 g of urea, stirred at 45°C for 30 min to trigger the confined regrowth process, cooled to room temperature, centrifuged, washed with water for 3 times, and then dispersed in 40 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL), 20 mL of alkaline sodium hypochlorite oxidizing solution is added, stirred for 25 min, centrifuged, washed with anhydrous ethanol for 2 times, and then nano CoOOH precursor B is obtained;

[0040] (6) The nano CoOOH precursor B obtained in step (5) is added into 130 mL of anhydrous ethanol, 2 g of 3-chloropropyltrimethoxysilane and 0.8 mL of deionized water are added, and the mixture is reacted at 68°C for 40 min under nitrogen protection, centrifuged, vacuum dried at 60°C for 6 h, dispersed in 140 mL of N,N-dimethylformamide, 4 g of sodium p-toluenesulfonate is added, and the mixture is reacted at 80°C for 6 h under nitrogen protection, centrifuged, washed with deionized water for 3 times, and vacuum dried at 60°C for 12 h to obtain a nano CoOOH precursor containing initiation sites;

[0041] (7) The nano CoOOH precursor containing initiation sites obtained in step (6) and 6 g of 2-methyl-2-oxazoline are added into 100 mL of anhydrous acetonitrile, and the mixture is reacted at 78°C for 8 h under nitrogen atmosphere, 6 g of 2-nonyl-2-oxazoline is then added, and the mixture is continuously reacted at 78°C for 8 h, centrifuged, washed with anhydrous ethanol for 3 times, and vacuum dried at 60°C for 12 h to obtain nano cobalt hydroxyl oxide.

[0042] Example 2:

[0043] (1) 400 mL of deionized water, 18 g of cobalt nitrate hexahydrate, and 25 g of urea are sequentially added into a 1000 mL beaker, stirred and dissolved, 8 g of n-butylamine and 4 g of n-dodecylamine are then added, the mixture is stirred at room temperature for 30 min, heated to 65°C and kept stirring for 90 min, and then cooled to room temperature to obtain a uniform suspension;

[0044] (2) The uniform suspension obtained in step (1) is added into 50 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL), stirred for 15 min, kept stirring at 45°C for 45 min, centrifuged, washed with water for 3 times, and then dispersed in 50 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL) to obtain a nano Co(OH)2 precursor slurry;

[0045] (3) 30 g of sodium hypochlorite and 15 g of sodium hydroxide are dissolved in 250 mL of deionized water to obtain an alkaline sodium hypochlorite oxidizing solution;

[0046] (4) Under ice-bath condition, 200 mL of alkaline sodium hypochlorite oxidation solution was added dropwise into the nano Co(OH)2 precursor slurry obtained in step (2), stirred at 15°C for 25 min, centrifuged, washed with anhydrous ethanol for 2 times, and then nano CoOOH precursor A was obtained;

[0047] (5) The nano CoOOH precursor A obtained in step (4) was added into 300 mL of deionized water, 4 g of n-butylamine, 2 g of n-dodecylamine, and 15 g of urea, stirred at 50°C for 35 min, triggered the confined regrowth process, cooled to room temperature, centrifuged, washed with water for 3 times, and then dispersed in 50 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL), 30 mL of alkaline sodium hypochlorite oxidation solution was added, stirred for 30 min, centrifuged, washed with anhydrous ethanol for 2 times, and then nano CoOOH precursor B was obtained;

[0048] (6) The nano CoOOH precursor B obtained in step (5) was added into 150 mL of anhydrous ethanol, 3 g of 3-chloropropyltrimethoxysilane and 1 mL of deionized water were added, reacted at 70°C for 50 min under nitrogen protection, centrifuged, vacuum dried at 60°C for 6 h, dispersed in 150 mL of N,N-dimethylformamide, 5 g of sodium p-toluenesulfonate was added, reacted at 85°C for 8 h under nitrogen protection, centrifuged, washed with deionized water for 3 times, vacuum dried at 60°C for 12 h, and then the nano CoOOH precursor containing initiation sites was obtained;

[0049] (7) The nano CoOOH precursor containing initiation sites obtained in step (6) and 8 g of 2-methyl-2-oxazoline were added into 120 mL of anhydrous acetonitrile, reacted at 80°C for 10 h under nitrogen atmosphere, 8 g of 2-nonyl-2-oxazoline was further added, and the reaction was continued at 80°C for 10 h, centrifuged, washed with anhydrous ethanol for 3 times, and vacuum dried at 60°C for 12 h, and then the nano cobalt hydroxyl oxide was obtained.

[0050] Example 3:

[0051] (1) 450 mL of deionized water, 20 g of cobalt nitrate hexahydrate, and 30 g of urea were sequentially added into a 1000 mL beaker, stirred and dissolved, 10 g of n-butylamine and 6 g of n-dodecylamine were added, stirred at room temperature for 35 min, then heated to 70°C and kept stirring for 120 min, and then cooled to room temperature to obtain a uniform suspension;

[0052] (2) The uniform suspension obtained in step (1) was added into 60 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL), stirred for 20 min, then kept stirring at 50°C for 60 min, centrifuged, washed with water for 3 times, and then dispersed in 60 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL) to obtain a nano Co(OH)2 precursor slurry;

[0053] (3) 36 g of sodium hypochlorite and 18 g of sodium hydroxide were dissolved in 250 mL of deionized water to obtain an alkaline sodium hypochlorite oxidizing solution;

[0054] (4) 230 mL of the alkaline sodium hypochlorite oxidizing solution was added dropwise to the nano Co(OH)2 precursor slurry obtained in step (2) under ice-bath conditions, and stirred at 18°C for 30 min. After centrifugal separation and washing with anhydrous ethanol for 2 times, nano CoOOH precursor A was obtained;

[0055] (5) The nano CoOOH precursor A obtained in step (4) was added into 350 mL of deionized water, 5 g of n-butylamine, 3 g of n-dodecylamine, and 18 g of urea, and stirred at 55°C for 45 min to trigger the confined regrowth process. After cooling to room temperature, centrifugal separation, washing with water for 3 times, and re-dispersing in 60 mL of sodium hydroxide aqueous solution (concentration of 0.3 g / mL), 20 mL of alkaline sodium hypochlorite oxidizing solution was added, stirred for 35 min, centrifugal separation, and washing with anhydrous ethanol for 2 times to obtain nano CoOOH precursor B;

[0056] (6) The nano CoOOH precursor B obtained in step (5) was added into 180 mL of anhydrous ethanol, and then 4 g of 3-chloropropyltrimethoxysilane and 1.5 mL of deionized water were added. The mixture was reacted at 75°C for 70 min under nitrogen protection, centrifugal separation, vacuum drying at 60°C for 6 h, re-dispersing in 180 mL of N,N-dimethylformamide, adding 6 g of sodium p-toluenesulfonate, and reacting at 90°C for 10 h under nitrogen protection. After centrifugal separation, washing with deionized water for 3 times, and vacuum drying at 60°C for 12 h, the nano CoOOH precursor containing initiation sites was obtained;

[0057] (7) The nano CoOOH precursor containing initiation sites obtained in step (6) and 10 g of 2-methyl-2-oxazoline were added into 140 mL of anhydrous acetonitrile, and reacted at 82°C for 12 h under nitrogen atmosphere. Then 10 g of 2-nonyl-2-oxazoline was added, and the reaction was continued at 82°C for 12 h. After centrifugal separation and washing with anhydrous ethanol for 3 times, vacuum drying at 60°C for 12 h, the nano cobalt hydroxyl oxide was obtained.

[0058] Comparative Example 1:

[0059] The difference between Comparative Example 1 and Example 2 is that no n-dodecylamine is added in step (1) (the amount is changed to 0 g), only 12 g of n-butylamine is added, and the rest of the conditions are the same as those in Example 2.

[0060] Comparative Example 2:

[0061] The difference between Comparative Example 2 and Example 2 is that no n-butylamine is added in step (1) (the amount is changed to 0 g), only 12 g of n-dodecylamine is added, and the rest of the conditions are the same as those in Example 2.

[0062] Comparative Example 3:

[0063] Comparative Example 3 differs from Example 2 in that the "confinement regrowth-reoxidation" process is cancelled, i.e. step (5) is omitted, and the nano CoOOH precursor A obtained in step (4) is directly used in step (6), and the rest of the conditions are consistent with Example 2.

[0064] Comparative Example 4:

[0065] Comparative Example 4 differs from Example 2 in that the low-temperature control is cancelled, and step (4) is carried out at 25°C by adding the alkaline oxidizing solution dropwise and stirring for 25 min, and the rest of the conditions are consistent with Example 2.

[0066] Comparative Example 5:

[0067] Comparative Example 5 differs from Example 2 in that no silane grafting is performed, step (6) is omitted, and the nano CoOOH precursor B obtained in step (5) is directly used in the polymerization reaction conditions of step (7) to attempt polymerization, and the rest of the conditions are consistent with Example 2.

[0068] Comparative Example 6:

[0069] Comparative Example 6 differs from Example 2 in that the surface polymerization is only carried out for the first segment of monomers, step (7) only adds 16 g of 2-methyl-2-oxazoline for 10 h, and no 2-nonyl-2-oxazoline is added, and the rest of the conditions are consistent with Example 2.

[0070] Comparative Example 7:

[0071] Comparative Example 7 differs from Example 2 in that the surface polymerization is only carried out for the second segment of monomers, step (7) only adds 16 g of 2-nonyl-2-oxazoline for 10 h, and no 2-methyl-2-oxazoline is added, and the rest of the conditions are consistent with Example 2.

[0072] Performance Test:

[0073] The following test electrode sheets were prepared using active material (Example 1-3 or corresponding comparative sample): SuperP conductive agent: PVDF binder = 8:1:1 (mass ratio), NMP slurry, uniformly coated on a copper foil, dried at 120°C for 12 h under vacuum, and rolled to a surface density of 1.5 mg / cm 2 ; button CR2032 half-cell (lithium sheet counter electrode, Celgard separator, 1M LiPF6 / EC:DEC=1:1 containing 5wt% FEC), tested after standing at 25°C for 12 h. Each sample has n≥3 parallel groups, and the average value is given.

[0074] X-ray diffraction test: The test results are shown in Figure 1 .

[0075] Infrared spectrum test: The infrared spectrometer was used for testing, and the results were as shown in Table 1. Figure 2

[0076] Thickness of nanometer hydroxyl cobalt oxide: The thickness of nanometer hydroxyl cobalt oxide was tested by atomic force microscopy, the tapping mode was used for testing, the silicon probe elastic coefficient was 42 N / m, the resonance frequency was about 320 kHz, the scanning rate was 0.5 Hz, the scanning range was 5 μm x 5 μm, the average thickness was tested by statistical analysis of at least 200 independent nanosheets, and the results were as shown in Table 1.

[0077] Specific surface area test: The specific surface area of nanometer hydroxyl cobalt oxide was tested by nitrogen adsorption BET method, the test was carried out at 77 K, the relative pressure range was P / P0 = 0.01-0.99, the linear interval in the range of P / P0 = 0.05-0.30 was used for calculating the BET specific surface area, and the results were as shown in Table 1.

[0078] Electrode surface resistance: The surface resistance was measured by four-probe method on the electrode coating side, the probe distance was 1.0 mm, the current was linearly scanned in the range of 1-10 mA to obtain the steady-state value, and the results were as shown in Table 1.

[0079] Rate performance: The rate performance test was carried out in the sequence of 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C and 10 C, each rate was cycled for 5 times, and finally returned to 0.1 C to verify the capacity recovery ability, the capacity was calculated by integrating the discharge platform, the reversible specific capacity at 10 C high rate was recorded, and the capacity recovery rate was recorded, and the results were as shown in Table 1.

[0080] Cycle stability test: 1000 times of charge-discharge cycles were carried out at 1 C rate, the capacity retention rate was calculated, and the results were as shown in Table 1.

[0081]

[0082] Data analysis:

[0083] ​As can be seen from the data of Examples 1-3 in Table 1, the nano-hydroxyl cobalt oxide prepared by the present application shows obvious performance adjustability under the comprehensive regulation of diamine synergistic confinement system and surface modification engineering, which embodies the effectiveness of process parameter optimization. With systematic adjustment of diamine ratio, oxidation conditions and polymerization parameters, the nano-sheet thickness, specific surface area, surface resistance and electrochemical performance show regular change trends, among which Example 2 obtains the best comprehensive performance, indicating that there is an optimal process parameter window. This performance adjustability may be due to the precise control of the diamine synergistic confinement mechanism on the thickness of the nano-sheet in the hydrolysis-condensation-lamellar extension process, and the introduction of controllable ion / electron active channels while maintaining the lamellar lattice by the mild sodium hypochlorite oxidation and the reciprocating treatment of confined regrowth-reoxidation. The surface silane grafting and the construction of two-stage poly(2-oxazoline) brush layer further optimize the electrode-electrolyte interface, which adjusts the microenvironment and reduces the interface impedance through the hydrophilic-hydrophobic double block structure.

[0084] As can be seen from the data of Example 2 and Comparative Example 1 in Table 1, the diamine synergistic confinement strategy shows significant advantages in nano-sheet morphology control and electrochemical performance compared with the single n-butylamine system, which embodies the importance of the synergistic regulation of long and short chain amine molecules. Comparative analysis shows that the diamine system shows obvious technical effects in thickness control, specific surface area improvement, interface resistance reduction and rate performance improvement, which may be related to the synergistic mechanism of n-butylamine amino coordination confining lamellar extension and n-dodecylamine long-chain hydrophobic end capping the edge of the sheet. When n-butylamine is used alone, although the amino coordination can limit the lamellar growth to some extent, the lack of long-chain amine capping effect leads to inaccurate sheet thickness control, relatively low specific surface area, and increased sheet contact resistance. The difference in electrochemical performance shows that the ultra-thin nano-sheet structure constructed by the diamine synergistic system provides shorter diffusion paths and more active sites for lithium ions, and improves the charge transfer dynamics. The improvement of rate performance and cycle stability may be due to the formation of more uniform and stable nano-sheet structure under the regulation of diamine, as well as the improvement of electrode density and structural stability, which proves the key role of diamine synergistic confinement mechanism in the preparation of ultra-thin lamellar materials.

[0085] As can be seen from the data of Example 2 and Comparative Example 2 in Table 1, when only long-chain n-dodecylamine is used, the thickness of the nanosheet increases significantly, the specific surface area decreases substantially, the surface resistance rises sharply, and the electrochemical performance deteriorates severely, indicating that the end-capping effect of the hydrophobic long chain alone cannot achieve effective thickness confinement. This performance deterioration may be directly related to the absence of the coordination effect of the n-butylamine amino group. In the hydrolysis-condensation-lamellar extension process, the lack of coordination confinement of the short-chain amine makes it difficult to control the hydrolysis-condensation process of cobalt ions, resulting in the formation of thicker nanosheets and relatively rough surface morphology. Although long-chain n-dodecylamine has hydrophobic end-capping ability, its coordination ability is relatively weak and cannot achieve effective regulation of lamellar growth alone. The substantial decline in electrochemical performance reflects the adverse effects of thick nanosheet structure on lithium ion diffusion kinetics. The increased thickness lengthens the ion diffusion path, the reduced specific surface area reduces the active site density, and the high surface resistance indicates that the inter-sheet contact and electron transport are severely hindered.

[0086] As can be seen from the data of Example 2 and Comparative Example 3 in Table 1, when the confinement regrowth process is omitted and surface modification is directly performed, although the thickness of the nanosheet remains relatively thin, the specific surface area decreases, the surface resistance increases significantly, and the electrochemical performance decreases significantly, indicating that the primary oxidation treatment cannot fully optimize the microstructure and interface characteristics of the nanosheet. This may be because the first mild oxidation converts Co(OH)2 into a preliminary CoOOH structure, and the confinement regrowth process realizes the repair of lattice defects and further optimization of surface morphology through the re-introduction of a double amine system, and re-oxidation introduces more ion / electron active channels while maintaining the optimized morphology. This reciprocal treatment avoids structural damage that may be caused by one-time strong oxidation, and through mild step-by-step treatment, it introduces an appropriate amount of hydroxyl vacancies and interlayer mismatches while maintaining the integrity of the lamellar lattice, thereby improving the charge storage and transport characteristics.

[0087] As can be seen from the data of Example 2 and Comparative Example 4 in Table 1, when the oxidation reaction is carried out at room temperature, the thickness of the nanosheet increases slightly, the specific surface area decreases, the surface resistance remains relatively low but the electrochemical performance deteriorates significantly, especially the rate performance and cycle stability decrease substantially, indicating that temperature control is crucial to maintaining the integrity of the nanosheet structure and electrochemical stability. This may be because, under ice bath conditions, the oxidation reaction rate of sodium hypochlorite is effectively controlled, avoiding local over-oxidation and structural defects that may be caused by too fast oxidation, making the conversion process of Co(OH)2 to CoOOH more uniform and mild.

[0088] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, when surface polymerization is carried out directly without silane grafting, the thickness and specific surface area of ​​the nanosheets remain basically the same, but the sheet resistivity increases significantly, and the rate performance and cycle stability decrease significantly. This indicates that silanization treatment has a decisive influence on the interface engineering and surface modification effects. Without silane grafting, the direct polymerization reaction lacks effective initiation sites and interfacial bonding forces, resulting in the inability of polymer chains to form a uniform and dense brush layer structure on the nanosheet surface.

[0089] As can be seen from the data in Table 1 for Examples 2, 6, and 7, the two-stage polymerization strategy demonstrates superior interface control compared to single polymerization, highlighting the importance of the hydrophilic-hydrophobic diblock structure. The technical advantage of the two-stage polymerization likely stems from the precise control of the electrolyte microenvironment by the hydrophilic-hydrophobic diblock structure: the first stage, the hydrophilic inner layer formed by 2-methyl-2-oxazoline, provides excellent lithium-ion transport channels and electrolyte wettability, ensuring basic electrochemical reactivity; the second stage, the hydrophobic outer layer formed by 2-nonyl-2-oxazoline, acts as a selective barrier, regulating the distribution and diffusion behavior of the electrolyte on the electrode surface and potentially inhibiting certain side reactions, thus improving interfacial stability. This gradient interfacial structure optimizes the long-term stability and anti-attenuation capability of the electrode while ensuring ion transport efficiency.

[0090] from Figure 1 It can be seen that the sample exhibits typical layered CoOOH diffraction characteristics, with a strong and significantly broadened (003) peak near 20.2°, and diffraction peaks of (101), (012), (015), (110), and (113) appearing successively at 37.0°, 38.9°, 50.7°, 65.4°, and 69.3°, indicating that the product is a rhombohedral polymorphic CoOOH phase. Due to the material being an ultrathin nanosheet, the (003) peak is significantly broadened. At the same time, the crescent-shaped background in the 15–30° range and the slight granular noise at the peak top are consistent with the amorphous scattering and noise characteristics caused by the surface poly(2-oxazoline) brush layer and adsorbed water.

[0091] from Figure 2 It can be seen that, compared to precursor B, the modified nano-cobalt hydroxyl oxide at 1648 cm⁻¹... -1 A distinct new absorption peak appears at 1105 cm⁻¹ (attributed to the amide-like C=O of poly(2-oxazoline)). -1 With approximately 1030cm -1 A COC and Si-O-Si overlapping reinforcement band appears at 2920 / 2850 cm⁻¹. -1 The CH stretching peaks were also significantly enhanced, indicating the successful introduction of silane anchoring and the polymerized brush layer; meanwhile, both peaks at 620 / 520 cm⁻¹ were also significantly enhanced. -1The Co-O skeleton vibrations of both CoOOH and CoOOH / GO were retained, indicating that the surface modification did not change the layered skeleton of CoOOH. The broad O-H band (~3405 cm -1 ) of the modified sample was relatively weakened, and the H2O bending band (~1630 cm -1 ) was partially covered by C=O absorption, reflecting the regulation of the brush layer on the interface hydroxyl and adsorbed water.

[0092] Those skilled in the art should understand: the above discussion of any embodiment is only exemplary, and is not intended to imply that the scope of the present application is limited to these examples; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in details.

Claims

1. A method for preparing nanohydroxyl cobalt oxide, characterized in that, It comprises the following steps: S1: stirring cobalt nitrate hexahydrate, urea, n-butylamine, n-dodecylamine and deionized water at room temperature for 25-35 min, then heating to 60-70℃ and keeping stirring for 60-120 min, cooling to room temperature to obtain a uniform suspension; S2: adding the uniform suspension obtained in step S1 into sodium hydroxide aqueous solution, stirring for 12-20 min, then keeping stirring at 40-50℃ for 40-60 min, centrifuging, washing with water, and dispersing in sodium hydroxide aqueous solution to obtain a nano Co(OH)2 precursor slurry; S3: under ice bath condition, adding alkaline sodium hypochlorite oxidizing solution dropwise into the nano Co(OH)2 precursor slurry obtained in step S2, heating to 12-18℃ and stirring for 20-30 min, centrifuging, and washing to obtain nano CoOOH precursor A; S4: adding the nano CoOOH precursor A obtained in step S3 into deionized water, then adding n-butylamine, n-dodecylamine and urea, stirring at 45-55℃ for 30-45 min, cooling to room temperature, centrifuging, washing with water, and dispersing in sodium hydroxide aqueous solution, then adding alkaline sodium hypochlorite oxidizing solution, stirring for 25-35 min, centrifuging, and washing to obtain nano CoOOH precursor B; S5: adding the nano CoOOH precursor B obtained in step S4 into anhydrous ethanol, then adding 3-chloropropyltrimethoxysilane and deionized water, reacting at 68-75℃ for 40-70 min under nitrogen protection, centrifuging, vacuum drying, dispersing in N,N-dimethylformamide, adding sodium p-toluenesulfonate, reacting at 80-90℃ for 6-10 h under nitrogen protection, centrifuging, washing with water, and vacuum drying to obtain a nano CoOOH precursor containing initiating sites; S6: adding the nano CoOOH precursor containing initiating sites obtained in step S5 and 2-methyl-2-oxazoline into anhydrous acetonitrile, reacting at 78-82℃ for 8-12 h under nitrogen atmosphere, then adding 2-nonyl-2-oxazoline, and continuing to react at 78-82℃ for 8-12 h, centrifuging, washing, and vacuum drying to obtain nano hydroxyl cobalt oxide; The amount of cobalt nitrate hexahydrate is 16-20 g; In step S1, the amount of urea is 20-30 g, the amount of n-butylamine is 6-10 g, the amount of n-dodecylamine is 3-6 g, and the amount of deionized water is 350-450 mL; In step S4, the amount of deionized water is 280-350 mL, the amount of n-butylamine is 3-5 g, the amount of n-dodecylamine is 1.5-3 g, the amount of urea is 12-18 g, the amount of sodium hydroxide aqueous solution is 40-60 mL, and the amount of alkaline sodium hypochlorite oxidizing solution is 20-30 mL; In step S6, the amount of 2-methyl-2-oxazoline is 6-10 g, the amount of 2-nonyl-2-oxazoline is 6-10 g, and the amount of anhydrous acetonitrile is 100-140 mL.

2. The method for preparing nano-cobalt hydroxyl oxide according to claim 1, characterized in that, The concentration of the sodium hydroxide aqueous solution is 0.3 g / mL.

3. The method for preparing nano-cobalt hydroxyl oxide according to claim 1, characterized in that, The first amount of the aqueous sodium hydroxide solution in step S2 is 40-60 mL, and the second amount of the aqueous sodium hydroxide solution is 40-60 mL, based on 16-20 g of cobalt nitrate hexahydrate.

4. The method for preparing nano-cobalt hydroxyl oxide according to claim 1, characterized in that, The basic sodium hypochlorite oxidizing solution is prepared from sodium hypochlorite, sodium hydroxide and deionized water, and the ratio of the sodium hypochlorite, sodium hydroxide and deionized water is 24-35 g: 12-18 g: 250 mL.

5. The method for preparing nano-cobalt hydroxyl oxide according to claim 1, characterized in that, The amount of the basic sodium hypochlorite oxidizing solution in step S3 is 160-230 mL, based on 16-20 g of cobalt nitrate hexahydrate.

6. The method for preparing nano-cobalt hydroxyl oxide according to claim 1, characterized in that, The amount of the anhydrous ethanol in step S5 is 130-180 mL, the amount of 3-chloropropyltrimethoxysilane is 2-4 g, the amount of the deionized water is 0.8-1.5 mL, the amount of N,N-dimethylformamide is 140-180 mL, and the amount of sodium p-toluenesulfonate is 4-6 g, based on 16-20 g of cobalt nitrate hexahydrate.

7. Nanohydroxyl cobalt oxide characterized in that, The nano-hydroxyl cobalt oxide is prepared by the method of any one of claims 1-6.

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