Preparation method for realizing coating of main material carbon nano tube

Abstract

The invention belongs to the technical field of battery materials, and discloses a preparation method for realizing coating of a main material carbon nanotube. The preparation method comprises the following steps: adding a carbon nanotube into a solvent containing a dispersant, and carrying out ultrasonic treatment; the preparation method comprises the following steps: under the protection of inert gas, adding a lithium source, an iron source and a phosphorus source into a reaction container, adding a solvent, and stirring to form a lithium iron phosphate precursor solution; slowly adding the dispersed carbon nanotube suspension into the lithium iron phosphate precursor solution, and stirring while adding; carrying out hydrothermal reaction or solvothermal reaction on the mixed solution; after the reaction is finished, cooling, filtering and washing a product, and drying the washed product; and carrying out high-temperature annealing treatment on the dried product. According to the coating method provided by the invention, the application performance of the coated battery material can be comprehensively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a preparation method for realizing main material carbon nanotube coating. BACKGROUND

[0002] Although carbon coating can improve the electronic conductivity of lithium iron phosphate to some extent, its conductive performance still has room for further improvement under the existing technology. For example, the current carbon coating layer may have uneven or discontinuous problems, resulting in imperfect electronic transmission channels and affecting the rate performance and charge-discharge efficiency of the battery. By improving the carbon coating technology, such as optimizing the selection of carbon source and improving the coating process, the carbon layer can be more uniformly and densely coated on the surface of lithium iron phosphate particles, forming a more effective conductive network, thereby further improving the electronic conductivity of the material and meeting the demand for high-power output and fast charge-discharge of electric vehicles and the like.

[0003] The ion diffusion rate also needs to be improved. Although carbon coating has a certain promoting effect on the diffusion of lithium ions, the existing technology level cannot make lithium ions migrate fully and quickly inside the material. Improving the carbon coating technology can optimize the microstructure of the material, reduce the resistance of lithium ion diffusion, and improve the ion diffusion rate, thereby improving the low-temperature performance and rate performance of the battery.

[0004] Improving the rate performance: In some high-power application scenarios, such as electric tools, hybrid electric vehicles, etc., the battery needs to provide a large amount of electric energy in a short time, which puts higher requirements on the rate performance of lithium iron phosphate. Although the existing carbon coating technology has improved the rate performance to some extent, it still cannot fully meet the application demand of fast charge-discharge. For example, during high-current charge-discharge, the capacity of the battery decays quickly and the performance decreases significantly. Therefore, it is necessary to further improve the carbon coating technology to improve the rate performance of lithium iron phosphate so that it can better adapt to high-power application scenarios.

[0005] Optimizing the low-temperature performance: The migration rate of lithium ions of the existing lithium iron phosphate battery will decrease significantly in a low-temperature environment, resulting in a decrease in the charge-discharge performance of the battery, which is manifested as a slow charging speed and a decrease in discharge capacity of the battery in a low-temperature environment. Although carbon coating can alleviate the low-temperature performance problem to some extent, the effect is limited. By improving the carbon coating technology, such as developing a carbon coating layer with a special structure and finding a more suitable carbon source for a low-temperature environment, the performance of the lithium iron phosphate battery in a low-temperature environment can be further improved, the application range thereof is expanded, and it can be normally used in cold regions.

[0006] In terms of cost control, firstly, the cost of raw materials: some carbon source materials used for carbon coating currently have high costs, or require complex processes and equipment during preparation, leading to increased production costs. By improving technology, cheaper and more widely available carbon sources can be found, or the efficiency of carbon source use can be optimized to reduce raw material costs. For example, exploring the use of some discarded biomass materials as carbon sources can not only reduce costs, but also achieve resource reuse. Secondly, production efficiency: existing carbon coating production processes may have complex processes, long production cycles, and low equipment utilization, resulting in low production efficiency and increased production costs. Improving technology can optimize production processes, improve the automation level of production equipment, and increase production efficiency to reduce the production cost per unit of product. For example, using more advanced continuous production processes can reduce downtime and waiting time in intermediate stages, improve production efficiency, reduce costs, and enhance the market competitiveness of products.

[0007] In terms of quality stability, firstly, uniformity of coating: existing carbon coating technologies may not be able to guarantee uniform carbon layer coating on the surface of lithium iron phosphate particles in some cases, and may result in partial areas being coated too thickly or too thinly, or even not being coated at all. This can lead to inconsistencies in battery performance, affecting the overall quality and reliability of the battery. By improving the coating process, such as using more precise control methods and optimizing reaction conditions, the uniformity of carbon coating can be improved to ensure that each lithium iron phosphate particle is uniformly covered with a carbon layer, thereby improving the stability and consistency of battery performance. Secondly, batch stability: in actual production, different batches of products may differ in carbon coating effectiveness due to fluctuations in raw materials, changes in process parameters, and other factors, affecting the batch stability of the products. Improving technology can enhance the monitoring and management of the production process, improve the stability and controllability of the process, reduce differences between batches, ensure the stability of product quality, and meet the needs of large-scale production and application. SUMMARY

[0008] In view of the poor performance of carbon coating in improving the electronic conductivity and other properties of lithium iron phosphate, the present application aims to provide a preparation method for realizing main material carbon nanotube coating, which can comprehensively improve the performance of coated battery materials.

[0009] A preparation method for realizing main material carbon nanotube coating, the preparation method comprising the following steps:

[0010] S1 adding carbon nanotubes to a solvent containing a dispersant and performing ultrasonic treatment;

[0011] S2 under the protection of an inert gas, adding a lithium source, an iron source, and a phosphorus source to a reaction container, then adding an appropriate amount of solvent, stirring uniformly, and forming a lithium iron phosphate precursor solution;

[0012] S3 slowly adds the dispersed carbon nanotube suspension into the lithium iron phosphate precursor solution while stirring;

[0013] S4 transfers the mixed solution into a reaction kettle to perform hydrothermal reaction or solvothermal reaction;

[0014] S5 after the reaction, cools the product, filters, washes, dries the washed product; and performs high-temperature annealing treatment on the dried product.

[0015] Further, the dispersant in S1 is a combination of fatty amine polyoxyethylene ether and dodecyl betaine; the ultrasonic time is 1-3h, and the ultrasonic power is 250-450W; the dispersant accounts for 0.5%-1.2% of the solvent, and the carbon nanotube accounts for 2%-4% of the solvent; and the solvent is water.

[0016] Further, the lithium source is any one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the iron source is any one of iron oxide, iron phosphate, or ferrous oxalate; the phosphorus source is any one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate; and the solvent is water.

[0017] Still further, the lithium source, the iron source, and the phosphorus source are combined in a molar ratio of 3-1:1:1.

[0018] Further, the reaction temperature in S4 is 120-200℃, and the reaction time is 12-24h.

[0019] Further, the washing in S5 is performed using deionized water and / or an ethanol solution until the pH value of the filtrate is neutral; and the high-temperature annealing treatment is heating the product to 500-800℃ under inert gas protection for 4-8h.

[0020] Further, the inert gas in S2 or S5 is any one of helium, neon, and argon.

[0021] Compared with the prior art, the application has the following advantages:

[0022] (1) Since some battery materials have poor electrical conductivity, and the carbon nanotube has a unique one-dimensional nanostructure and high electron mobility, coating the carbon nanotube on the surface of the material can construct an efficient conductive network between the material particles, provide a fast channel for electron transmission, significantly improve the electronic conductivity of the material, and thus improve the charge and discharge efficiency and rate performance of the battery device, such as the electrode material of a lithium ion battery, the carbon nanotube coating can make the electrode charge and discharge faster at a high current density; the carbon nanotube can promote the transmission of electric charge in the electrode material, reduce the charge transfer resistance, and improve the power density of the battery, so that the battery can quickly output or store electric energy to meet the demand for high-power equipment such as electric vehicles.

[0023] (2) In the process of battery charging and discharging, the potential of the electrode material will change. The carbon nanotube coating layer can play a buffering role, stabilize the potential of the electrode material, reduce the influence of potential fluctuation on the performance of the battery, and thus improve the cycle stability and service life of the battery.

[0024] (3) Carbon nanotubes have high strength and modulus. After being coated on the surface of the material, it is like adding a layer of strong "armor" to the material, which can effectively improve the overall mechanical strength of the material, making it less likely to break or damage when subjected to external forces; for some materials that will experience mechanical stress during use, such as the volume change of battery electrodes during charging and discharging cycles, the carbon nanotube coating layer can alleviate this stress, prevent the collapse of the material structure, and maintain the integrity and performance stability of the material.

[0025] (4) The preparation method of the present application can make the nanoscale and flexible structure of carbon nanotubes give the coated material better flexibility; this enables the material to adapt to different shapes and deformation requirements, and has important application value in the fields of flexible electronic devices, wearable devices, etc., such as materials in flexible display screens and smart bracelets and other products.

[0026] (5) Preventing active substance dissolution: In some battery systems, the active substance of the electrode material may dissolve in the electrolyte, leading to battery capacity decay. The carbon nanotube coating layer can act as a physical barrier to prevent direct contact between the active substance and the electrolyte, reducing the occurrence of dissolution phenomena, thereby maintaining the capacity and performance of the battery.

[0027] (6) The coating layer can reduce the interfacial reactivity between the material and the electrolyte, reducing side reactions at the interface, such as electrolyte decomposition, excessive growth of SEI film (solid electrolyte interface film), etc., which helps to maintain the stability of the electrode interface, improve the cycle performance and safety of the battery.

[0028] (7) Carbon nanotube coating can to some extent inhibit the particle agglomeration and growth of the material during preparation and use, making the microstructure of the material more stable and maintaining good dispersibility, thereby fully exerting its performance advantages.

[0029] (8) Carbon nanotubes have good thermal conductivity, and after coating, they can improve the thermal conductivity efficiency of the material, help dissipate heat, reduce the risk of thermal runaway of the material in a hot environment, and improve the thermal stability and safety of the material, which is particularly important for devices such as batteries that work in high-temperature environments. DETAILED DESCRIPTION

[0030] The following provides a specific embodiment of a method for preparing a main material carbon nanotube coated product. It is necessary to point out that the following examples are only used to explain the present application in more detail, and are not intended to limit the scope of the present application. Improvements and adjustments made by those skilled in the art after reading the present application without departing from the concept of the present application are within the scope of the present application.

[0031] A method for preparing a main material carbon nanotube coated product:

[0032] Step 1: Carbon nanotube dispersion: Add carbon nanotubes to a solvent containing a dispersant, and perform ultrasonic treatment, wherein the ultrasonic treatment time is 1-3h, and the ultrasonic power is 250-450W.

[0033] Step 2: Preparation of lithium iron phosphate precursor: Under the protection of an inert gas, add a lithium source, an iron source, and a phosphorus source to a reaction vessel in a stoichiometric ratio (Li:Fe:P=3-1:1:1), add an appropriate amount of solvent, and stir uniformly to form a lithium iron phosphate precursor solution; the lithium source is any one of lithium carbonate, lithium hydroxide, or lithium dihydrogen phosphate, the iron source is any one of iron oxide, iron phosphate, or ferrous oxalate, the phosphorus source is any one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or lithium dihydrogen phosphate, the solvent is water, and the inert gas is any one of helium, neon, or argon.

[0034] Step 3: Mixing of carbon nanotubes and lithium iron phosphate precursor: Slowly add the dispersed carbon nanotube suspension to the lithium iron phosphate precursor solution while stirring, and the stirring time is not less than 2h to ensure that the carbon nanotubes and the lithium iron phosphate precursor are fully mixed.

[0035] Step 4: Reaction process: Transfer the mixed solution to a reaction kettle, and perform hydrothermal or solvothermal reaction; the reaction temperature is between 120-200℃, and the reaction time is 12-24h. During the reaction process, lithium iron phosphate gradually grows on the surface of the carbon nanotubes, achieving coating of the carbon nanotubes.

[0036] Step 5: Product treatment: After the reaction is completed, cool the product to room temperature, then filter and wash to remove impurities and unreacted substances. Washing can be performed multiple times using deionized water or an ethanol solution of any concentration until the pH value of the filtrate is neutral. Dry the washed product at 60-80℃ for 12-24h to remove residual solvent. Perform high-temperature annealing treatment on the dried product, i.e., heat the product to 500-800℃ under the protection of an inert gas, and maintain the temperature for 4-8h to improve the crystallinity and electrochemical performance of the product, achieving coating of the main material carbon nanotubes.

[0037] Example 1

[0038] A method for preparing a main material carbon nanotube coated product:

[0039] Step 1 Carbon nanotube dispersion: Carbon nanotubes are added to a solvent containing a dispersant and subjected to ultrasonic treatment, with an ultrasonic time of 2 h and an ultrasonic power of 400 W.

[0040] Step 2 Preparation of lithium iron phosphate precursor: Under the protection of inert gas, lithium source, iron source and phosphorus source are added to the reaction container in stoichiometric ratio (Li:Fe:P = 1:1:1), and an appropriate amount of solvent is added, stirred uniformly to form a lithium iron phosphate precursor solution; the lithium source is lithium dihydrogen phosphate, the iron source is iron oxide, the phosphorus source is ammonium dihydrogen phosphate, the solvent is water, and the inert gas is argon.

[0041] Step 3 Mixing of carbon nanotubes and lithium iron phosphate precursor: The dispersed carbon nanotube suspension is slowly added to the lithium iron phosphate precursor solution while stirring, and the stirring time is 3 h to ensure that the carbon nanotubes and lithium iron phosphate precursor are fully mixed.

[0042] Step 4 Reaction process: The mixed solution is transferred to the reaction kettle for hydrothermal reaction; the reaction temperature is between 120-200℃, and the reaction time is 12-24h.

[0043] Step 5 Product treatment: After the reaction is completed, the product is cooled to room temperature, then filtered and washed to remove impurities and unreacted substances. Deionized water is used for multiple washings until the pH of the filtrate is neutral. The washed product is dried at 60-80℃ for 12-24h to remove residual solvent. The dried product is subjected to high-temperature annealing treatment, i.e. heating the product to 600℃ under the protection of inert gas for 6h.

[0044] Performance testing of the product obtained in Example 1:

[0045] The coated lithium iron phosphate is subjected to structural characterization, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), etc. to determine the coating of carbon nanotubes and the crystal structure of lithium iron phosphate; electrochemical performance tests such as charge-discharge test, cyclic voltammetry test, AC impedance test, etc. are carried out to evaluate the specific capacity, cycle performance and rate performance of the coated lithium iron phosphate; the experimental results are shown in Table 1.

[0046] Table 1. Test items and experimental results

[0047]

[0048] In addition, due to the interconnection of the structure, the three-dimensional carbon-based nanostructure has the advantages of multistage porous channels, high conductivity and excellent structural mechanical stability. The lithium iron phosphate is attached to the three-dimensional platform to form a composite material, which has the advantages of flexibility and mechanical properties, chemical and thermal stability and large specific surface area, and the electrochemical performance is significantly improved. The carbon coating not only improves the conductivity, but also prevents Fe 2+ oxidation into Fe 3+ .

[0049] The prepared positive electrode material is a three-dimensional conductive grid, and the results show that the discharge specific capacity is 155 mAh / g at 0.1C rate, which is higher than most LiFPO4 batteries on the market.

[0050] The method provided by the application can increase the carbon coating area, make the active material contact with more electrolyte, and further improve the electrochemical performance.

[0051] Description: The above examples are only used to illustrate the application and not to limit the technical solutions described in the application; therefore, although the application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the application can still be modified or replaced; all technical solutions and improvements that do not deviate from the spirit and scope of the application should be covered in the application.

Claims

1. A method for preparing a substrate by coating carbon nanotubes, characterized in that, The preparation method includes the following: S1 involves adding carbon nanotubes to a solvent containing a dispersant and then subjecting them to ultrasonic treatment; Under inert gas protection, lithium source, iron source and phosphorus source are added to the reaction vessel, followed by solvent and stirring to form lithium iron phosphate precursor solution; S3 slowly adds the well-dispersed carbon nanotube suspension to the lithium iron phosphate precursor solution while stirring. S4 will perform a hydrothermal or solvothermal reaction on the mixed solution; After the S5 reaction is completed, the product is cooled, filtered, washed, and dried; the dried product is then subjected to high-temperature annealing.

2. The preparation method for coating the main material with carbon nanotubes according to claim 1, characterized in that, The dispersant in S1 is a combination of fatty amine polyoxyethylene ether and dodecyl betaine; the ultrasonic time is 1-3 hours, and the ultrasonic power is 250-450W; the dispersant accounts for 0.5%-1.2% of the solvent, and the carbon nanotubes account for 2-4% of the solvent; the solvent is water.

3. The preparation method for coating the main material with carbon nanotubes according to claim 2, characterized in that, The lithium source is any one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the iron source is any one of iron oxide, iron phosphate, and ferrous oxalate; the phosphorus source is any one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate; and the solvent is water.

4. The preparation method for coating the main material with carbon nanotubes according to claim 3, characterized in that, The lithium source, iron source, and phosphorus source are combined in a molar ratio of 3 to 1:1:

1.

5. The preparation method for coating the main material with carbon nanotubes according to claim 4, characterized in that, The reaction temperature in step S4 is between 120-200℃, and the reaction time is 12-24h.

6. The preparation method for coating the main material with carbon nanotubes according to claim 1, characterized in that, The washing in step S5 is performed using deionized water and / or ethanol solution until the pH of the filtrate is neutral; the high-temperature annealing treatment is performed by heating the product to 500-800℃ and holding it at that temperature for 4-8 hours under inert gas protection.

7. The preparation method for coating the main material with carbon nanotubes according to claim 1, characterized in that, The inert gas used in step S2 or S5 is any one of helium, neon, or argon.

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