Method for preparing thin-layer carbon coated positive electrode material by adopting liquid-phase organic carbon source

Abstract

The invention relates to a method for preparing a thin-layer carbon-coated positive electrode material by adopting a liquid-phase organic carbon source, which comprises the following steps of: introducing a liquid-phase organic matter serving as a carbon source into a positive electrode active material system such as lithium iron phosphate, forming an adsorption or interface modification structure on the surface of a positive electrode material particle by the carbon source, performing solid-liquid separation, and performing in-situ carbonization under a protective atmosphere to obtain the thin-layer carbon-coated positive electrode material. And constructing a continuous thin-layer carbon coating structure on the surfaces of the positive electrode material particles to obtain the thin-layer carbon coated positive electrode material. The method is simplified in process, convenient to operate, low in cost and suitable for large-scale preparation; the obtained material is good in carbon layer continuity and high in interface stability, and is beneficial to improvement of electronic conductivity and reduction of electrode polarization, so that the rate capability and the cycle stability are improved, meanwhile, the particle surface structure stability can be improved, transition metal dissolution is inhibited in the cycle process, and the long-term cycle stability of an electrode is improved. The method is suitable for various lithium ion battery positive electrode material systems, and is especially suitable for lithium ion batteries with relatively high requirements on rate capability and cycle life.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source. Background Technology

[0002] Lithium-ion batteries possess outstanding advantages such as high energy density, no memory effect, fast charge and discharge speed, long cycle life, and low self-discharge rate, making them the dominant energy storage technology in portable electronic devices, power tools, mobile power supplies, new energy vehicles, and large-scale energy storage facilities. Common lithium-ion battery cathode materials include lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium-rich manganese-based materials, high-nickel ternary materials, lithium manganese iron phosphate, and spinel-type manganese-based cathode materials.

[0003] Among them, lithium iron phosphate (LFP) cathode materials exhibit good structural stability, thermal stability, and safety performance, and are widely available, low-cost, and environmentally friendly. However, these materials typically suffer from low intrinsic electronic conductivity, which limits their rate performance and low-temperature performance to some extent. To address this issue, existing technologies usually employ methods such as adding conductive agents or surface carbon coating to improve the material's conductivity.

[0004] In existing technologies, conductive materials such as carbon black, carbon nanotubes, and graphene are mostly present in the form of added conductive agents. Their contact with cathode material particles is primarily physical, resulting in limited interfacial bonding and a tendency for uneven dispersion or interfacial detachment, thus affecting the stability of the conductive network. In contrast, constructing a continuous and dense carbon coating layer on the surface of cathode material particles helps shorten the electron transport path, reduce interfacial charge transfer impedance, and form a stable conductive network, thereby significantly improving the material's rate performance and cycle stability.

[0005] Currently, most common carbon coating methods for cathode materials employ solid-phase carbon sources. For example, patent CN115763734A discloses a method for preparing carbon-coated lithium iron phosphate. This method involves ball milling and mixing the precursor material with the lithium source and carbon source, followed by drying and high-temperature heat treatment to carbonize the carbon source and form a carbon coating layer. However, this type of method still has the following shortcomings: (1) The carbon source is mostly in solid form, and its introduction process mainly relies on mechanical mixing and dispersion, which is easily affected by powder agglomeration and dispersion state, resulting in limited consistency and controllability of the coating layer; (2) The mechanical mixing process has high requirements for equipment and process conditions, and the processing time is long, making it difficult to control batch stability during large-scale production; (3) The continuity and thickness uniformity of the carbon coating layer depend to some extent on the uniformity of carbon source distribution, which can easily lead to insufficient local coating, affecting the overall conductivity and cycle consistency of the material.

[0006] Therefore, it is still necessary to develop a new method for preparing thin-layer carbon-coated cathode materials. This method introduces an organic carbon source into a liquid-phase system, allowing the carbon source molecules to be uniformly distributed on the surface of the cathode material particles through adsorption or interface modification. The carbon source molecules are then carbonized in situ during subsequent heat treatment to form a continuous carbon layer. This improves the uniformity and controllability of the carbon coating layer, simplifies the process, and facilitates large-scale stable preparation. Summary of the Invention

[0007] The purpose of this invention is to address the problems of complex carbon source mixing processes and insufficient coating uniformity and controllability in existing cathode material carbon coating processes, and to provide a method for preparing thin-layer carbon-coated cathode materials using liquid-phase organic carbon sources. This method uses liquid-phase organic matter as the carbon source, and through liquid-phase interface control, the organic carbon source forms a uniform adsorption or interface modification structure on the surface of the cathode active material particles. In-situ carbonization is then carried out during subsequent heat treatment to form a continuous thin-layer carbon coating structure. This method features a simplified process, convenient operation, low cost, and suitability for large-scale preparation. The resulting thin-layer carbon-coated cathode material exhibits advantages such as good coating layer continuity and high interface stability, which is beneficial for improving the material's conductivity, rate performance, and cycle stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source includes the following steps: (1) Using an organic carbon source as a liquid carbon source, add it to an organic solvent and stir at room temperature to form a homogeneous solution to obtain a carbon source solution; the organic carbon source accounts for 0.1-50% of the volume fraction of the organic solvent; (2) Add the positive electrode active material particles to the carbon source solution obtained in step (1), and after ultrasonic treatment, stir and disperse to allow the organic carbon source to be adsorbed or modified on the surface of the positive electrode active material particles to obtain a surface-modified positive electrode material suspension; the ratio of the positive electrode active material added to the carbon source solution in step (1) is 5 to 300 mg / mL. (3) The cathode material suspension obtained in step (2) is subjected to solid-liquid separation to obtain precursor material. Heat treatment is carried out under a protective atmosphere to carbonize the liquid phase organic matter in situ, forming a continuous carbon layer on the surface of the cathode active material particles, and obtaining a thin-layer carbon-coated cathode material.

[0009] In this invention, the organic carbon source in step (1) is a long-chain organic compound containing polar functional groups. The polar functional groups are selected from one or more of carboxyl, amino, phosphonic acid, phosphate or phosphate ester groups. The long-chain organic compound is a C4 to C20 aliphatic organic compound.

[0010] In this invention, the long-chain organic compounds containing polar functional groups include oleylamine, eicosamine, hexadecamine, dodecylamine, decylamine, octylamine, hexylamine, butylamine; oleic acid, icosanoic acid, hexadecanoic acid, dodecanoic acid, decanoic acid, octanoic acid, hexanoic acid, butyric acid; octadecylphosphonic acid, hexadecylphosphonic acid, dodecylphosphonic acid, or oleyl phosphate esters, or one or more of these.

[0011] In this invention, the organic solvent in step (1) is selected from one or more of n-hexane, cyclohexane, petroleum ether, toluene, ethanol, methanol, acetone, ethyl acetate, diethyl ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, chloroform, or dichloromethane.

[0012] In this invention, the positive electrode active material in step (2) is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium-rich manganese-based material, high-nickel ternary material, lithium manganese iron phosphate, or spinel-type manganese-based positive electrode material.

[0013] In this invention, the ultrasonic treatment time in step (2) is 1 to 60 min, the stirring time is 0.5 to 12 h, and the stirring speed is 200 to 800 rpm.

[0014] In this invention, the solid-liquid separation method in step (3) includes one or more of the following: pressure filtration, vacuum filtration, centrifugal separation, static sedimentation or solvent evaporation; the protective atmosphere is an inert atmosphere, which is selected from nitrogen, argon or a combination thereof.

[0015] In this invention, the heating rate in step (3) is 1 to 10 ℃ / min, and the heat treatment includes multiple heat preservation processes, wherein the temperature of the first stage is 80 to 150 ℃, the temperature of the second stage is 300 to 500 ℃, the temperature of the third stage is 600 to 800 ℃, and the heat preservation time of each stage is 0.1 to 3 h.

[0016] In this invention, the thickness of the carbon layer formed is 0.5–10 nm.

[0017] By adopting the above technical solution, the present invention has the following beneficial effects: (1) This invention uses liquid organic matter as a carbon source. Through solution mixing and dispersion treatment, the carbon source is uniformly introduced onto the surface of the positive electrode material particles and then carbonized in situ by heat treatment to form a continuous thin-layer carbon coating structure. The process is simplified, the operation is convenient, and it is suitable for large-scale preparation. (2) The present invention eliminates the complex mixing process of solid carbon source, such as mechanical dispersion process such as ball milling, which helps to reduce production complexity and manufacturing cost; (3) The method of the present invention can be directly applied to commercial cathode material systems, has good universality, can be applied to multiple types of lithium-ion battery systems, and has strong adaptability; (4) The thin carbon coating layer formed by the present invention has good continuity and controllability, which is conducive to building a stable conductive channel, reducing the interface charge transfer impedance, thereby improving the rate performance and cycle stability of the material. (5) The thin carbon coating structure formed can improve the stability of the particle surface interface, suppress the dissolution of transition metals during cycling, and help improve the long-term cycling stability of the electrode. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the surface morphology of the thin-layer carbon-coated cathode material particles obtained in Example 1; Figure 2 for Figure 1 A magnified view of a portion of the image, used to show the structural features of the thin carbon coating on the surface of the cathode material particles; Figure 3 This is a transmission electron microscope image of the thin-layer carbon-coated cathode material obtained in Example 1; Figure 4 This is a transmission electron microscope image of the thin-layer carbon-coated cathode material obtained in Example 2; Figure 5 Raman spectra of the example sample and the commercial cathode material control sample; Figure 6 This is a comparison chart of the rate performance of the example sample and the commercial cathode material control sample. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments. This embodiment uses lithium iron phosphate as a representative cathode material, but the present invention is equally applicable to other lithium-ion battery cathode material systems. The scope of protection of the present invention is not limited thereto. Example 1

[0020] A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source, wherein lithium iron phosphate is used as a representative cathode material, and the specific steps are as follows: (1) Preparation of liquid-phase organic carbon source solution Take 1 mL of oleic acid and 1 mL of oleylamine as liquid-phase organic carbon sources, add them to 8 mL of n-hexane solution, and stir at room temperature for 3 min to form a homogeneous solution to obtain the carbon source solution.

[0021] (2) Preparation of cathode material suspension The positive electrode active material (lithium iron phosphate is used as an example in this embodiment) is added to the carbon source solution obtained in step (1), and after ultrasonic treatment at room temperature for 10 min, it is stirred and dispersed for 6 h to form an adsorption or interface modification structure on the surface of the positive electrode material particles by liquid organic carbon source, and a positive electrode material suspension is obtained.

[0022] (3) Preparation of thin-layer carbon-coated cathode material The suspension obtained in step (2) was filtered to obtain the precursor material. Then it was placed in a tube furnace and heat-treated under a nitrogen protective atmosphere. The temperature was increased to 120 ℃ at 2 ℃ / min and held for 30 min, then increased to 400 ℃ and held for 1 h, and finally increased to 700 ℃ and held for 2 h to carbonize the liquid phase organic carbon source in situ and form a continuous carbon layer on the surface of the cathode material particles to obtain a thin-layer carbon-coated cathode material. Example 2

[0023] A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source, the steps of which are the same as in Example 1, the difference being: (1) Preparation of liquid-phase organic carbon source solution Take 5 mL of oleic acid as a liquid organic carbon source and add it to 45 mL of n-hexane solution. Stir at room temperature for 5 min to form a homogeneous solution and obtain the carbon source solution.

[0024] (2) Preparation of cathode material suspension The positive electrode active material (lithium iron phosphate is used as an example in this embodiment) is added to the carbon source solution obtained in step (1), and ultrasonically treated for 10 min at room temperature, and then stirred and dispersed for 8 h to obtain a positive electrode material suspension.

[0025] (3) Prepare thin-layer carbon-coated cathode material, and follow the same solid-liquid separation and heat treatment steps as in Example 1.

[0026] Example 3 A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source, the steps of which are the same as in Example 1, the difference being: (1) Preparation of liquid-phase organic carbon source solution Take 10 mL of oleic acid and 10 mL of oleylamine as liquid-phase organic carbon sources, add them to 80 mL of n-hexane solution, and stir at room temperature for 15 min to form a homogeneous solution, thus obtaining the carbon source solution.

[0027] (2) Preparation of cathode material suspension The positive electrode active material (lithium iron phosphate is used as an example in this embodiment) is added to the carbon source solution obtained in step (1), and ultrasonically treated at room temperature for 20 min, and then stirred and dispersed for 12 h to obtain a positive electrode material suspension.

[0028] (3) Preparation of thin-layer carbon-coated cathode material The suspension obtained in step (2) was centrifuged to separate the solid precursor material; then it was heat-treated under an argon protective atmosphere, with the same heating procedure as in Example 1.

[0029] Example 4 A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source, wherein lithium nickel cobalt manganese oxide ternary material is used as the cathode active material, and the specific steps are as follows: (1) Preparation of liquid-phase organic carbon source solution Take 1.5 mL of oleylamine as a liquid organic carbon source and add it to 30 mL of ethanol solution. Stir at room temperature for 5 min to form a homogeneous solution and obtain the carbon source solution.

[0030] (2) Preparation of cathode material suspension The positive electrode active material (in this embodiment, lithium nickel cobalt manganese oxide is used as an example) is added to the carbon source solution obtained in step (1), and after ultrasonic treatment at room temperature for 15 min, it is stirred and dispersed for 5 h to form an adsorption or interface modification structure on the surface of the positive electrode material particles, thereby obtaining a positive electrode material suspension.

[0031] (3) Preparation of thin-layer carbon-coated cathode material The suspension obtained in step (2) was centrifuged to separate the solid precursor material. Then it was placed in a tube furnace and heat-treated under an argon protective atmosphere. The temperature was increased to 100 ℃ at 3 ℃ / min and held for 1 h, then increased to 550 ℃ and held for 2 h to carbonize the liquid organic carbon source in situ and form a continuous carbon layer on the surface of the positive electrode active material particles to obtain a thin-layer carbon-coated positive electrode material.

[0032] Example 5 A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source, wherein lithium manganese oxide is used as the cathode active material, and the specific steps are as follows: (1) Preparation of liquid-phase organic carbon source solution Take 0.8 mL of dodecylphosphonic acid as a liquid organic carbon source and add it to 25 mL of toluene solution. Stir at room temperature for 10 min to form a homogeneous solution and obtain the carbon source solution.

[0033] (2) Preparation of cathode material suspension The positive electrode active material (lithium manganese oxide is used as an example in this embodiment) is added to the carbon source solution obtained in step (1), and after ultrasonic treatment at room temperature for 25 min, it is stirred and dispersed for 8 h to form an adsorption or interface modification structure on the surface of the positive electrode material particles by liquid organic carbon source, and a positive electrode material suspension is obtained.

[0034] (3) Preparation of thin-layer carbon-coated cathode material The suspension obtained in step (2) was filtered to obtain the precursor material. Then it was placed in a tube furnace and heat-treated under a nitrogen protective atmosphere. The temperature was increased to 120 ℃ at 4 ℃ / min and held for 40 min, then increased to 350 ℃ and held for 1.5 h, and finally increased to 600 ℃ and held for 1 h, so that the liquid phase organic carbon source was carbonized in situ and a continuous carbon layer was formed on the surface of the positive electrode active material particles to obtain a thin-layer carbon-coated positive electrode material.

[0035] Test results The thin-layer carbon-coated cathode material obtained in Example 1 (in this example, it is a lithium iron phosphate system) was observed using a high-resolution transmission electron microscope, and the results are as follows: Figure 1 and Figure 2 As shown, where Figure 1 The overall morphology of carbon coating on the particle surface. Figure 2 A close-up of a thin-layer carbon structure.

[0036] Figure 3 and Figure 4 The images are transmission electron microscope images of the samples obtained in Examples 2 and 3, respectively.

[0037] Figure 5 The images show the Raman spectra of the samples from Examples 1-3 and the control sample of the commercial cathode material. The results indicate that the sample of the present invention exhibits Raman spectra at approximately 1350 cm⁻¹. -1 and 1590 cm -1 A distinct carbon structure characteristic peak appears at this location.

[0038] Figure 6 The results of the rate performance comparison between the samples of Examples 1-3 and the commercial cathode material control sample show that the samples of the present invention are significantly better than the commercial cathode material in terms of capacity retention and high-rate charge-discharge performance.

Claims

1. A method for preparing thin-layer carbon-coated cathode materials using a liquid-phase organic carbon source, characterized in that, Includes the following steps: (1) Using an organic carbon source as a liquid carbon source, add it to an organic solvent and stir at room temperature to form a homogeneous solution to obtain a carbon source solution; the organic carbon source accounts for 0.1-50% of the volume fraction of the organic solvent; (2) Add the positive electrode active material particles to the carbon source solution obtained in step (1), and after ultrasonic treatment, stir and disperse to allow the organic carbon source to be adsorbed or modified on the surface of the positive electrode active material particles to obtain a surface-modified positive electrode material suspension; the ratio of the positive electrode active material added to the carbon source solution in step (1) is 5 to 300 mg / mL. (3) The cathode material suspension obtained in step (2) is subjected to solid-liquid separation to obtain precursor material. Heat treatment is carried out under a protective atmosphere to carbonize the liquid phase organic matter in situ, forming a continuous carbon layer on the surface of the cathode active material particles, and obtaining a thin-layer carbon-coated cathode material.

2. The method according to claim 1, characterized in that, The organic carbon source in step (1) is a long-chain organic compound containing polar functional groups. The polar functional groups are selected from one or more of carboxyl, amino, phosphonic acid, phosphate or phosphate ester groups. The long-chain organic compound is a C4 to C20 aliphatic organic compound.

3. The method according to claim 2, characterized in that, The long-chain organic compounds containing polar functional groups include oleylamine, eicosamine, hexadecamine, dodecylamine, decylamine, octylamine, hexylamine, butylamine; oleic acid, icosanoic acid, hexadecanoic acid, dodecanoic acid, decanoic acid, octanoic acid, hexanoic acid, butyric acid; octadecylphosphonic acid, hexadecylphosphonic acid, dodecylphosphonic acid or oleyl phosphate esters, or one or more of these.

4. The method according to claim 1, characterized in that, The organic solvent mentioned in step (1) is selected from one or more of n-hexane, cyclohexane, petroleum ether, toluene, ethanol, methanol, acetone, ethyl acetate, diethyl ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, chloroform or dichloromethane.

5. The method according to claim 1, characterized in that, The positive electrode active material mentioned in step (2) is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium-rich manganese-based material, high-nickel ternary material, lithium manganese iron phosphate, or spinel-type manganese-based positive electrode material.

6. The method according to claim 1, characterized in that, In step (2), the ultrasonic treatment time is 1 to 60 min, the stirring time is 0.5 to 12 h, and the stirring speed is 200 to 800 rpm.

7. The method according to claim 1, characterized in that, In step (3), the solid-liquid separation method includes one or more of the following: pressure filtration, vacuum filtration, centrifugal separation, static sedimentation or solvent evaporation; the protective atmosphere is an inert atmosphere, which is selected from nitrogen, argon or a combination thereof.

8. The method according to claim 1, characterized in that, In step (3), the heating rate of the heat treatment is 1 to 10 ℃ / min. The heat treatment includes multiple heat treatment processes, in which the temperature of the first stage is 80 to 150 ℃, the temperature of the second stage is 300 to 500 ℃, the temperature of the third stage is 600 to 800 ℃, and the heat treatment time of each stage is 0.1 to 3 h.

9. The method according to claim 1, characterized in that, The thickness of the carbon layer formed is 0.5–10 nm.

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