Microporous carbon coated core-shell nano composite material, preparation method and application

Abstract

The invention discloses a microporous carbon-coated core-shell nano composite material, a preparation method and application, and relates to the technical field of lithium batteries, and the preparation method comprises the following steps: uniformly dispersing silicon powder and graphite in a solvent to form a core material suspension; dopamine hydrochloride and hydrogen peroxide are added into the nuclear material suspension, polymerization reaction is carried out at the temperature of 60-85 DEG C, composite slurry is obtained, and the ratio of the total mass of the silicon powder and the graphite to the mass of the dopamine hydrochloride is 1: (0.1-0.5); carrying out spray drying treatment on the composite slurry to obtain precursor powder; sintering the precursor powder at high temperature to obtain a microporous carbon coated core-shell nano composite material; the microporous carbon-coated silicon / graphite core-shell nano composite material is prepared by adopting a polydopamine in-situ polymerization technology initiated by hydrogen peroxide and combining a subsequent spray drying and carbonization process, and the material has good rate capability, cycling stability, charge-discharge efficiency and low interface impedance.

Description

A microporous carbon-coated core-shell nanocomposite material, its preparation method and application Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a microporous carbon-coated core-shell nanocomposite material, its preparation method, and its application. Background Technology

[0002] In the fabrication of silicon-carbon anodes, the uniformity of the carbon coating layer has a crucial impact on the performance of the anode material. A uniform carbon coating layer can more effectively mitigate the volume expansion of silicon particles during charge and discharge, prevent the pulverization and breakage of silicon particles, and thus improve the cycle stability of the anode material. A uniform carbon coating layer can improve the overall conductivity of the silicon-carbon anode, reduce the internal resistance of the battery, and improve charge and discharge efficiency. A uniform carbon coating layer also helps to improve the interfacial stability between silicon particles and electrolyte, reduce the occurrence of side reactions, and protect silicon particles from electrolyte corrosion. However, achieving a uniform and dense protective coating on the surface of layered oxide particles in battery materials remains a technical challenge.

[0003] One of the most significant and unique properties of polydopamine (PDA) is its excellent adhesion, a characteristic that makes it promising for applications in materials science, biomedicine, environmental science, and many other fields. The main advantages of PDA coatings lie in their strong coating properties and good interfacial compatibility. The catechol and amino functional groups in the PDA molecule allow it to be firmly adsorbed onto the surface of layered oxides through various chemical interactions (such as hydrogen bonding and metal coordination). This coating not only enhances the adhesion between the layered oxides and the electrolyte but also improves their compatibility with other organic materials.

[0004] In existing technologies, methods using polydopamine-assisted carbon coating of silicon-based materials typically focus on forming dense or composite graphene coating layers. However, the adaptability of these structures to the rapid transport of lithium ions and the volume expansion of silicon is still not ideal. This is mainly reflected in the following aspects: although dense carbon layers can provide conductivity and certain mechanical support, they limit the ion diffusion rate and are prone to cracking under repeated expansion and contraction; while introducing two-dimensional materials such as graphene can enhance conductivity and flexibility, their coating structures are often difficult to construct uniformly, firmly, and with abundant pores at the nanoscale, leading to a decrease in interface stability during long-term cycling; in addition, existing processes often involve multi-step wet composite and separation processes, which are complex to operate and make it difficult to precisely control the pore structure and thickness uniformity of the coating layer, which is not conducive to the large-scale preparation of high-performance, structurally consistent silicon-carbon composite anode materials.

[0005] Based on this, a microporous carbon-coated core-shell nanocomposite material, its preparation method, and its application are provided to solve the above problems. Summary of the Invention

[0006] This invention aims to address the technical problems of existing carbon-coated layers having poor mechanical properties, being unable to adapt to volume changes in the silicon core, being prone to cracking, and having poor interfacial bonding with the silicon core, resulting in poor cycle stability and interfacial stability. The purpose is to provide a microporous carbon-coated core-shell nanocomposite material, its preparation method, and its application. By employing hydrogen peroxide-induced in-situ polymerization of polydopamine, combined with subsequent spray drying and carbonization processes, a microporous carbon-coated silicon / graphite core-shell nanocomposite material is prepared. This material exhibits good rate performance, cycle stability, charge-discharge efficiency, and low interfacial impedance.

[0007] This invention is achieved through the following technical solution:

[0008] The first objective of this invention is to provide a method for preparing a microporous carbon-coated core-shell nanocomposite material, comprising the following steps:

[0009] Silicon powder and graphite are evenly dispersed in a solvent to form a suspension of nuclear materials;

[0010] Dopamine hydrochloride and hydrogen peroxide are added to a nuclear material suspension, and a polymerization reaction is carried out in the temperature range of 60-85℃ to obtain a composite slurry, wherein the mass ratio of the total mass of silicon powder and graphite to the mass of dopamine hydrochloride is 1:(0.1-0.5).

[0011] The composite slurry was spray-dried to obtain precursor powder;

[0012] Precursor powder was sintered at high temperature to obtain a core-shell nanocomposite material coated with microporous carbon.

[0013] The microporous carbon-coated silicon / graphite core-shell nanocomposite material prepared by this invention, using hydrogen peroxide-initiated in-situ polymerization of polydopamine combined with subsequent spray drying and carbonization processes, exhibits several advantages, as detailed below:

[0014] First, the polydopamine layer formed with the assistance of hydrogen peroxide is carbonized and transformed into a carbon shell with a nanoscale microporous structure. These micropores provide additional channels for the rapid transport of lithium ions, effectively reducing the ion diffusion resistance and thus improving the rate performance of the material.

[0015] Secondly, the microporous carbon shell has both good mechanical flexibility and a certain elastic buffer space, which can more effectively adapt to the volume change of the silicon core during charging and discharging, reducing material pulverization and structural collapse. This is reflected in its significantly improved cycle stability, such as higher capacity retention after long-cycle operation.

[0016] Furthermore, in-situ polymerization ensures a strong interfacial bond between the carbon coating layer and the silicon / graphite core, while spray drying ensures the uniformity and dispersion of the particles. This results in a more stable conductive network and lower interfacial impedance in the composite material throughout the electrode, leading to a reduction in battery internal resistance and an improvement in charge-discharge efficiency.

[0017] Furthermore, the process is simple and coherent, easy to scale up and control, and provides a feasible technical solution for the large-scale and consistent production of high-performance silicon-carbon anode materials.

[0018] Furthermore, the mass ratio of silicon powder to graphite is 1:(0.5-2).

[0019] Furthermore, the hydrogen peroxide used is hydrogen peroxide with a concentration of 20-30%.

[0020] Furthermore, the amount of hydrogen peroxide added is: for every 1g of total mass of silicon powder and graphite, 0.4-1.0mL of hydrogen peroxide with a concentration of 20-30% is added.

[0021] Furthermore, the polymerization reaction time is 3-6 hours.

[0022] Furthermore, the high-temperature sintering temperature is 600-900℃, and the sintering time is 2-4 hours.

[0023] Furthermore, the high-temperature sintering is carried out under an inert atmosphere.

[0024] The second objective of this invention is to provide a microporous carbon-coated core-shell nanocomposite material, prepared by the aforementioned method.

[0025] The third objective of this invention is to provide an application of a microporous carbon-coated core-shell nanocomposite material in lithium batteries.

[0026] A fourth objective of this invention is to provide a lithium battery comprising a microporous carbon-coated core-shell nanocomposite material as described above, which serves as a negative electrode material.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] 1. This invention utilizes hydrogen peroxide to assist in the formation of a polydopamine layer, which, after carbonization, transforms into a carbon shell with a nanoscale microporous structure. These micropores provide additional channels for the rapid transport of lithium ions, effectively reducing ion diffusion resistance and thus improving the rate performance of the material. Furthermore, this microporous carbon shell possesses good mechanical flexibility and a certain elastic space, enabling it to more effectively adapt to the volume changes of the silicon core during charge and discharge, reducing material pulverization and structural collapse, significantly improving the cycle stability of the material, and enhancing capacity retention after long-cycle operation. Simultaneously, in-situ polymerization ensures a strong interfacial bond between the carbon coating layer and the silicon / graphite core, while spray drying ensures particle uniformity and dispersion, resulting in a more stable conductive network and lower interfacial impedance throughout the electrode, effectively reducing battery internal resistance and improving charge and discharge efficiency.

[0029] 2. The process flow is simple and coherent, easy to scale up and control, and provides a feasible technical solution for the large-scale and consistent production of high-performance silicon-carbon anode materials.

[0030] 3. This invention uses hydrogen peroxide as an initiator and does not contain any other metal impurities, thus avoiding the negative impact of introducing metal impurities on the battery interface stability and ensuring the cycle stability and interface stability of the material. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 is a morphology diagram of the composite material prepared in Example 3; Figure 2 is a morphology diagram of the composite material prepared in Comparative Example 2. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0033] The following details the embodiments of a microporous carbon-coated core-shell nanocomposite material, its preparation method, and its applications according to the present invention. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0034] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0035] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0038] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0039] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0040] It should be noted that, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0041] Example 1

[0042] A method for preparing a microporous carbon-coated core-shell nanocomposite material includes the following steps:

[0043] 10 g of silicon nanoparticles and 5 g of graphite powder (mass ratio 2:1) were added to 200 mL of deionized water and dispersed by high-speed shearing for 30 minutes to form a uniform suspension. The suspension was transferred to a reactor, heated to 70 °C, and stirred continuously. Separately, a 25% hydrogen peroxide solution was prepared, and 8 mL was slowly added dropwise to the reactor. Subsequently, 2 g of dopamine hydrochloride was dissolved in 20 mL of Tris-HCl buffer (pH=8.5) and slowly injected into the reaction system. In-situ polymerization was carried out at 70 °C for 5 hours. After the reaction, the resulting dark brown slurry was spray-dried at an inlet air temperature of 180 °C and an outlet air temperature of 95 °C to obtain precursor powder. This powder was placed in a tube furnace and heated to 750 °C at a rate of 5 °C / min under argon protection, held for 3 hours, and then naturally cooled to obtain a microporous carbon-coated silicon / graphite composite anode material.

[0044] TEM characterization showed that a uniform carbon layer with a thickness of about 20-30 nm and rich nanopores was formed on the surface of the silicon / graphite core.

[0045] Example 2

[0046] A method for preparing a microporous carbon-coated core-shell nanocomposite material includes the following steps:

[0047] A 12g silicon-to-graphite composite (1:1 mass ratio) was dispersed in 150ml of a mixture of ethanol and water and dispersed under high-speed shear for 30 minutes to form a homogeneous suspension. The suspension was transferred to a reactor, heated to 60°C, and continuously stirred. 6ml of 20% hydrogen peroxide was used as an initiator. Subsequently, 1.2g of dopamine hydrochloride (making the silicon / graphite composite to dopamine hydrochloride mass ratio 1:0.1) was dissolved in 15ml of Tris-HCl buffer (pH=8.5) and slowly injected into the reaction system. The reaction temperature was controlled at 60°C, and the polymerization time was extended to 6 hours to ensure complete coating. After the reaction, spray drying was performed with inlet air temperature set to 160°C and outlet air temperature to 85°C to obtain precursor powder. This powder was placed in a tube furnace and heated to 650°C at a rate of 5°C / min under argon protection, held at that temperature for 4 hours, and then allowed to cool naturally to obtain a microporous carbon-coated silicon / graphite composite anode material.

[0048] The obtained material, as shown by nitrogen adsorption testing, exhibits a BET specific surface area of ​​220 m² for its carbon coating. 2 The pore size distribution is concentrated in the range of 2-5 nm, confirming the existence of a microporous structure. This structure effectively buffers the volume change during cycling. After 300 cycles at 1C, the particle integrity remains good, with no obvious pulverization.

[0049] Example 3

[0050] A method for preparing a microporous carbon-coated core-shell nanocomposite material includes the following steps:

[0051] A silicon / graphite composite with a mass ratio of 1:2 (15 g) was dispersed in 150 mL of a mixed solvent of ethanol and water. The dispersion was subjected to high-speed shear dispersion for 30 minutes to form a homogeneous suspension. The suspension was transferred to a reactor, heated to 85 °C, and continuously stirred. 4.5 g of dopamine hydrochloride (silicon / graphite composite to dopamine hydrochloride mass ratio of 1:0.3) was dissolved in 40 mL of Tris-HCl buffer (pH=8.5) and slowly injected into the reaction system. 10 mL of 30% hydrogen peroxide was added, and the polymerization reaction was carried out at a higher temperature of 85 °C for 3 hours. Under these conditions, the polymerization rate was accelerated, and the resulting polydopamine coating was more dense. After the reaction, spray drying was performed with inlet air temperature set to 160 °C and outlet air temperature to 85 °C to obtain the precursor powder. Then, under argon protection, the carbon is heated to a higher temperature of 900℃ at 5℃ / min for 2 hours to obtain a carbon layer with a higher degree of graphitization. After natural cooling, a silicon / graphite composite anode material with microporous carbon coating is obtained.

[0052] The morphology of the obtained material is shown in Figure 1. It can be observed that the silicon / graphite core is uniformly coated with a continuous and complete carbon layer, forming a clearly defined core-shell structure. The carbon coating layer has a uniform thickness (about 40-50 nm), a smooth and dense surface, and is tightly bonded to the core-shell interface. The overall particles are well dispersed, without obvious agglomeration, cracks, or structural defects. This directly confirms the significant effect of the present invention in controlling the uniformity of coating and structural integrity through in-situ polymerization initiated by hydrogen peroxide combined with spray drying.

[0053] Electrochemical tests showed that the material exhibited the highest initial coulombic efficiency (92.1%) and optimal cycling stability, maintaining a capacity retention of 91.8% after 500 cycles at 0.5C. Compared to Comparative Example 2, which relied solely on air oxidation without hydrogen peroxide initiation, the coating uniformity of this embodiment was significantly improved, the electrode compaction density was significantly increased, and the interfacial impedance was low, demonstrating the synergistic advantages of hydrogen peroxide-initiated in-situ polymerization combined with spray drying in controlling the material's morphology and structure.

[0054] Comparative Example 1

[0055] The difference between this embodiment and Embodiment 3 is that the polymerization reaction exceeds the set range of this invention, and is set at 90°C. Test results show that when the polymerization temperature exceeds 85°C, the excessively high polymerization temperature leads to an excessively fast dopamine polymerization rate, which easily results in uneven coating, high local defects, and reduced ability to form microporous structures and interfacial bonding strength after carbonization. This affects the volume adaptability and ion transport performance of the material during cycling, resulting in a significant decrease in cycling performance and a significant increase in electrode impedance.

[0056] Comparative Example 2

[0057] The difference between this embodiment and Example 1 is that hydrogen peroxide initiation and spray drying processes are not used. Instead, silicon, graphite, and dopamine hydrochloride are mixed in the proportions of Example 1, and polymerization is carried out solely by dissolved oxygen at the same temperature and pH. The slurry is then dried and ground in a conventional oven, followed by carbonization under the same conditions.

[0058] The morphology of the obtained material is shown in Figure 2. It can be observed that the material does not have a continuous and complete core-shell structure, the carbon coating layer is extremely unevenly distributed, the carbon layer is too thick in some areas while some core material is exposed, and there is severe agglomeration between composite particles. The carbon layer is also accompanied by structural defects such as pore collapse and fracture. These morphological shortcomings directly lead to a significant deterioration in the material's cycling performance (capacity retention rate of only 48.6% after 500 cycles at 0.5C), and a significant increase in electrode interface impedance, highlighting the necessity of the core process of this invention in controlling the morphology and performance of the material.

[0059] Comparative Example 3

[0060] The difference between this embodiment and Embodiment 1 is that ferric chloride is used as the oxidant instead of hydrogen peroxide, and polydopamine polymerization is carried out according to the material ratio of Embodiment 1. The subsequent processing is the same. Due to the introduction of iron ions, metallic impurities are introduced into the final material. Battery testing shows that the self-discharge rate of this material is significantly higher than that of the embodiments of this invention, and the cycle performance deteriorates. After 500 cycles at 0.5C, the capacity rapidly decays to less than 68% of the initial capacity, indicating that the metallic impurities have a negative impact on the battery interface stability.

[0061] The above embodiments and comparative examples were subjected to relevant performance tests. The test methods are as follows, and the test results are shown in Table 1.

[0062] 1. Half-cell assembly method: The negative electrode material, conductive carbon black (SuperP), and binder (PAA) prepared in the embodiments and comparative examples of this invention are mixed evenly in deionized water at a mass ratio of 80:10:10. The mixture is then coated onto a copper foil current collector, and the working electrode is obtained by vacuum drying, rolling, and stamping. A lithium metal sheet is used as the counter electrode, and a Celgard 2400 separator is used. The electrolyte is a solution of 1.0 mol / L LiPF6 dissolved in EC / DEC / DMC (volume ratio 1:1:1) with 10% FEC added. A CR2032 type coin cell half-cell is assembled in an argon-filled glove box.

[0063] 2. Cycle retention rate and conventional performance testing methods:

[0064] First discharge specific capacity and first coulombic efficiency (ICE): Under 25°C conditions, charge and discharge tests are performed at a rate of 0.05C within the range of 0.01-1.5 V. The ratio of the first discharge capacity to the charge capacity is the first coulombic efficiency.

[0065] Cycle retention rate: After initial activation, a long-cycle charge-discharge test is performed at a rate of 0.5C. The percentage of the discharge capacity after the Nth cycle to the discharge capacity of the first cycle is the cycle retention rate.

[0066] Compacted density: A certain mass of composite powder is placed in a mold and held under a fixed pressure (e.g., 2000 kg) for 30 seconds. The density is calculated by measuring the thickness, mass, and area of ​​the cylindrical electrode sheet.

[0067] Interfacial impedance (EIS): Using an electrochemical workstation, AC impedance is measured under conditions of 5 mV amplitude and a frequency range of 100 kHz to 0.01 Hz before battery cycling or after a specific number of cycles.

[0068] Table 1. Performance Test Results

[0069] Initial discharge specific capacity at 0.5C rate, mAh / g; initial coulombic efficiency, %; capacity retention after 500 cycles at 0.5C, %; compaction density, g / cm³. 3 Interface impedance, Ω⋅cm 2 Example 1: 125089.284.51.3845; Example 2: 121088.583.21.3552; Example 3: 118092.191.81.5538; Comparative Example 1: 115084.270.51.3078; Comparative Example 2: 108078.548.61.15125; Comparative Example 3: 112081.065.31.2895 surface

[0070] In summary, this invention utilizes hydrogen peroxide to assist in the formation of a polydopamine layer, which, after carbonization, transforms into a carbon shell with a nanoscale microporous structure. These micropores provide additional channels for the rapid transport of lithium ions, effectively reducing ion diffusion resistance and thus improving the rate performance of the material. Furthermore, this microporous carbon shell possesses good mechanical flexibility and a certain elastic space, enabling it to more effectively adapt to the volume changes of the silicon core during charge and discharge, reducing material pulverization and structural collapse, significantly improving the cycle stability of the material, and enhancing capacity retention after long-cycle operation. Simultaneously, in-situ polymerization ensures a strong interfacial bond between the carbon coating layer and the silicon / graphite core, while spray drying ensures particle uniformity and dispersion. This results in a more stable conductive network and lower interfacial impedance in the composite material throughout the electrode, effectively reducing battery internal resistance and improving charge and discharge efficiency. Consequently, the final composite material, when used as a negative electrode material, exhibits excellent rate performance, cycle stability, charge and discharge efficiency, and low interfacial impedance.

[0071] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing a microporous carbon-coated core-shell nanocomposite material, characterized in that, The process includes the following steps: dispersing silicon powder and graphite uniformly in a solvent to form a core material suspension; adding dopamine hydrochloride and hydrogen peroxide to the core material suspension and carrying out a polymerization reaction at a temperature range of 60-85℃ to obtain a composite slurry, wherein the mass ratio of the total mass of silicon powder and graphite to the mass of dopamine hydrochloride is 1:(0.1-0.5); spray drying the composite slurry to obtain a precursor powder; and sintering the precursor powder at high temperature to obtain a core-shell nanocomposite material coated with microporous carbon.

2. The method for preparing a microporous carbon-coated core-shell nanocomposite material according to claim 1, characterized in that, The mass ratio of silicon powder to graphite is 1:(0.5-2).

3. The method for preparing a microporous carbon-coated core-shell nanocomposite material according to claim 1, characterized in that, The hydrogen peroxide used is hydrogen peroxide with a concentration of 20-30%.

4. The method for preparing a microporous carbon-coated core-shell nanocomposite material according to claim 3, characterized in that, The amount of hydrogen peroxide added is: for every 1g of total mass of silicon powder and graphite, add 0.4-1.0mL of hydrogen peroxide with a concentration of 20-30%.

5. The method for preparing a microporous carbon-coated core-shell nanocomposite material according to claim 1, characterized in that, The polymerization reaction time is 3-6 hours.

6. The method for preparing a microporous carbon-coated core-shell nanocomposite material according to claim 1, characterized in that, The high-temperature sintering temperature is 600-900℃, and the sintering time is 2-4 hours.

7. The method for preparing a microporous carbon-coated core-shell nanocomposite material according to claim 1, characterized in that, The high-temperature sintering is carried out under an inert atmosphere.

8. A microporous carbon-coated core-shell nanocomposite material, characterized in that, Prepared by the method described in any one of claims 1-7.

9. The application of the microporous carbon-coated core-shell nanocomposite material as described in claim 8 in lithium batteries.

10. A lithium battery, characterized in that, This includes a microporous carbon-coated core-shell nanocomposite material as described in claim 8.

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