Silicon-carbon composite negative electrode structure with multiple levels of micropores

Abstract

The utility model provides a kind of silicon-carbon composite negative electrode structure with multistage micropore, it is related to lithium ion battery electrode material technical field, including core layer, transition layer, outer layer and conductive coating, the core layer is made of nanometer silicon particle and amorphous carbon composite, the nanometer silicon particle is uniformly dispersed in amorphous carbon matrix, the core layer inside forms primary micropore, the transition layer is coated in the outside of core layer.In the utility model, by core layer, transition layer and outer layer form gradually increasing primary micropore, secondary micropore and tertiary micropore from inside to outside aperture, these micropore can be classified and accommodate the volume expansion of nanometer silicon particle produced in charge-discharge process, relieve the stress brought by volume expansion, simultaneously provide more diffusion channel for lithium ion, shorten the diffusion path of lithium ion, cooperate the good conductivity of conductive network and graphite formed by carbon nanotube interweave in outer layer, improve the conductivity of electrode and lithium ion transmission efficiency.

Description

Technical Field

[0001] This utility model relates to the field of lithium-ion battery electrode materials technology, and in particular to a silicon-carbon composite negative electrode structure with multi-level micropores. Background Technology

[0002] In the field of lithium-ion batteries, silicon has become one of the most promising anode materials due to its extremely high theoretical specific capacity. However, silicon will produce huge volume expansion during charging and discharging, which can easily lead to the pulverization and shedding of electrode materials, causing the cycle performance of the battery to drop sharply and limiting its large-scale application.

[0003] In existing technologies, silicon is often combined with carbon materials to form silicon-carbon composite anodes to improve the volume expansion problem of silicon materials. However, in traditional silicon-carbon composite anode structures, the micropores are unevenly distributed and have a single pore size, which cannot effectively alleviate the volume expansion stress of silicon. At the same time, the diffusion path of lithium ions inside the electrode is relatively long, resulting in poor rate performance of the battery. In addition, the conductivity of some composite structures is poor, which affects the overall performance of the battery, thus requiring improvement. Summary of the Invention

[0004] This invention mainly provides a silicon-carbon composite negative electrode structure with multi-level micropores for lithium-ion battery electrode materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a silicon-carbon composite negative electrode structure with multi-level micropores, comprising a core layer, a transition layer, an outer layer, and a conductive coating. The core layer is composed of nano-silicon particles and amorphous carbon, with the nano-silicon particles uniformly dispersed in the amorphous carbon matrix. The core layer forms primary micropores. The transition layer covers the outside of the core layer and is composed of mesoporous carbon, forming secondary micropores. The outer layer covers the outside of the transition layer and is composed of graphite and carbon nanotubes, forming tertiary micropores. The conductive coating is coated on the surface of the outer layer and is composed of conductive carbon black and a binder.

[0006] Preferably, the pore size of the primary micropore is 2-5 nm, the pore size of the secondary micropore is 10-20 nm, and the pore size of the tertiary micropore is 30-50 nm. The pore sizes of the primary, secondary, and tertiary micropores gradually increase from the inside to the outside. Through this gradient micropore design, the inner layer of small pores can accurately buffer the initial expansion of the nano-silicon particles, while the outer layer of large pores provides sufficient deformation space for the overall structure, gradually dispersing the volume expansion stress. At the same time, the micropores of different sizes cooperate with each other to create more paths for lithium-ion diffusion and improve ion transport efficiency.

[0007] Preferably, the carbon nanotubes in the outer layer interweave to form a conductive network, and the graphite is uniformly distributed in the network formed by the carbon nanotubes. Through the high conductivity of the carbon nanotubes and the stable electron transport capability of the graphite, the two work together to construct an efficient conductive path, reduce electron transport resistance, significantly improve the overall conductivity of the electrode, and ensure smooth electron migration during the charging and discharging process of the battery.

[0008] Preferably, the core layer and the transition layer are tightly bonded by chemical bonds, and the transition layer and the outer layer are tightly bonded by chemical bonds. The strong connection of chemical bonds enhances the interfacial bonding force between the layers, avoids interlayer delamination caused by volume changes during charge and discharge cycles, ensures the integrity and stability of the electrode structure, and extends the service life of the electrode.

[0009] Preferably, the mass ratio of amorphous carbon in the core layer is 30%-50%, and the particle size of the nano-silicon particles is 50-200nm. By reasonably controlling the proportion of amorphous carbon, sufficient buffer matrix is ​​provided for the nano-silicon particles. At the same time, the nano-sized silicon particles can reduce the volume expansion. The combination of the two balances the capacity and structural stability of the electrode.

[0010] Preferably, the thickness of the transition layer is 1-3 μm and the thickness of the outer layer is 2-5 μm. By optimizing the thickness of the transition layer and the outer layer, it is possible to ensure that the transition layer effectively transmits and disperses the expansion stress of the core layer, while allowing the outer layer to fully exert its conductive and protective functions, thus avoiding performance impact due to insufficient thickness or increased electrode internal resistance due to excessive thickness.

[0011] Preferably, the thickness of the conductive coating is 0.5-1 μm, and the binder is polyvinylidene fluoride or sodium carboxymethyl cellulose. By controlling the coating thickness, good conductivity can be ensured while avoiding increasing the overall thickness of the electrode. As a binder, polyvinylidene fluoride or sodium carboxymethyl cellulose can not only firmly bond the conductive carbon black, but also form a stable bond with the outer layer material, ensuring that the coating does not fall off during cycling.

[0012] Compared with the prior art, the advantages and positive effects of this utility model are as follows: 1. In this utility model, primary, secondary, and tertiary micropores with gradually increasing pore size from the inside to the outside are formed by the core layer, transition layer, and outer layer. These micropores can accommodate the volume expansion of the nano-silicon particles during charging and discharging, alleviate the stress caused by the volume expansion, and provide more diffusion channels for lithium ions, shortening the diffusion path of lithium ions. Combined with the conductive network formed by the interwoven carbon nanotubes in the outer layer and the good conductivity of graphite, the conductivity of the electrode and the lithium ion transport efficiency are improved.

[0013] In this invention, the chemical bonds between the core layer and the transition layer, and between the transition layer and the outer layer, are tightly bonded, which enhances the connection stability between the layers and prevents the electrode from delaminating or falling off during cycling. The conductive coating is made of conductive carbon black and binder, which further improves the conductivity of the electrode surface, ensures smooth electron transmission, and extends the cycle life of the battery. Attached Figure Description

[0014] Figure 1 This invention presents an overall structural schematic diagram of a silicon-carbon composite negative electrode structure with multi-level micropores.

[0015] Legend: 1. Core layer; 2. Transition layer; 3. Outer layer; 4. Conductive coating. Detailed Implementation

[0016] To better understand the above-mentioned objectives, features, and advantages of this utility model, the present utility model will be further described below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0017] Many specific details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed in the following specification.

[0018] Please see Figure 1 This utility model provides a technical solution: a silicon-carbon composite negative electrode structure with multi-level micropores, including a core layer 1, a transition layer 2, an outer layer 3, and a conductive coating 4. The core layer 1 is composed of nano-silicon particles and amorphous carbon, with the nano-silicon particles uniformly dispersed in the amorphous carbon matrix. Primary micropores are formed inside the core layer 1. The transition layer 2 covers the outside of the core layer 1 and is composed of mesoporous carbon. Secondary micropores are formed inside the transition layer 2. The outer layer 3 covers the outside of the transition layer 2 and is composed of graphite and carbon nanotubes. Tertiary micropores are formed inside the outer layer 3. The conductive coating 4 is coated on the surface of the outer layer 3 and is composed of conductive carbon black and a binder.

[0019] like Figure 1 As shown, the pore size of the primary micropores is 2-5 nm, the pore size of the secondary micropores is 10-20 nm, and the pore size of the tertiary micropores is 30-50 nm. The pore sizes of the primary, secondary, and tertiary micropores gradually increase from the inside to the outside. Through this gradient micropore design, the inner layer of small pores can precisely buffer the initial expansion of the nano-silicon particles, while the outer layer of three large pores provides sufficient deformation space for the overall structure, dispersing the volume expansion stress step by step. At the same time, the micropores of different sizes cooperate with each other to create more paths for lithium-ion diffusion and improve ion transport efficiency.

[0020] like Figure 1 As shown, the carbon nanotubes in the outer layer 3 intertwine to form a conductive network, and graphite is uniformly distributed in the network formed by the carbon nanotubes. Through the high conductivity of carbon nanotubes and the stable electron transport capability of graphite, the two work together to construct an efficient conductive path, reduce electron transport resistance, significantly improve the overall conductivity of the electrode, and ensure smooth electron migration during the charging and discharging process of the battery.

[0021] like Figure 1 As shown, the core layer 1 and the transition layer 2 are tightly bonded by chemical bonds, and the transition layer 2 and the outer layer 3 are tightly bonded by chemical bonds. Through the strong connection of chemical bonds, the interfacial bonding force between the layers is enhanced, avoiding interlayer delamination caused by volume changes during charge and discharge cycles, ensuring the integrity and stability of the electrode structure, and extending the service life of the electrode.

[0022] like Figure 1 As shown, the mass ratio of amorphous carbon in core layer 1 is 30%-50%, and the particle size of nano-silicon particles is 50-200nm. By reasonably controlling the proportion of amorphous carbon, sufficient buffer matrix is ​​provided for nano-silicon particles. At the same time, the size of nano-sized silicon particles can reduce the volume expansion. The combination of the two balances the capacity and structural stability of the electrode.

[0023] like Figure 1 As shown, the thickness of the transition layer 2 is 1-3 μm, and the thickness of the outer layer 3 is 2-5 μm. By optimizing the thickness of the transition layer 2 and the outer layer 3, it is possible to ensure that the transition layer 2 effectively transmits and disperses the expansion stress of the core layer 1, while allowing the outer layer 3 to fully exert its conductive and protective functions, thus avoiding performance impact due to insufficient thickness or increased electrode internal resistance due to excessive thickness.

[0024] like Figure 1 As shown, the thickness of the conductive coating 4 is 0.5-1μm, and the binder is polyvinylidene fluoride or sodium carboxymethyl cellulose. By controlling the coating thickness, good conductivity is ensured while avoiding increasing the overall thickness of the electrode. As a binder, polyvinylidene fluoride or sodium carboxymethyl cellulose can not only firmly bond the conductive carbon black, but also form a stable bond with the outer layer 3 material, ensuring that the coating does not fall off during cycling.

[0025] The device's operation and working principle are as follows: During the charging and discharging process of a lithium-ion battery, lithium ions are deintercalated from the positive electrode and migrate through the electrolyte to the silicon-carbon composite negative electrode. They first reach the outer layer 3 and diffuse through the tertiary micropores of the outer layer 3. The conductive network formed by the interwoven carbon nanotubes and the uniformly distributed graphite in the outer layer 3 provide pathways for electron transport. Under the influence of an electric field, lithium ions continue to move through the secondary micropores of the transition layer 2 towards the core layer 1. The mesoporous carbon structure of the transition layer 2 further guides the diffusion of lithium ions. Finally, lithium ions are embedded in the nano-silicon particles and non-silicon nanoparticles through the primary micropores of the core layer 1. In the shaped carbon matrix, during discharge, lithium ions are deintercalated from the core layer 1 and diffuse back to the positive electrode along the original path. During this process, the primary micropores of the core layer 1, the secondary micropores of the transition layer 2, and the tertiary micropores of the outer layer 3 respectively accommodate the volume expansion of the nano-silicon particles to different degrees during charging and discharging. The chemical bonds between the core layer 1 and the transition layer 2, and between the transition layer 2 and the outer layer 3, ensure that each layer does not peel off during volume changes. The conductive coating 4 assists in electron transport on the surface of the outer layer 3. Throughout the process, the various structural components work together to complete the intercalation and deintercalation of lithium ions and the transport of electrons.

[0026] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present utility model without departing from the technical solution of the present utility model shall still fall within the protection scope of the technical solution of the present utility model.

Claims

1. A silicon-carbon composite anode structure with multi-level micropores, characterized in that, include: The core layer (1), transition layer (2), outer layer (3), and conductive coating (4) are composed of nano-silicon particles and amorphous carbon. The nano-silicon particles are uniformly dispersed in the amorphous carbon matrix. The core layer (1) forms primary micropores inside. The transition layer (2) covers the outside of the core layer (1). The transition layer (2) is composed of mesoporous carbon. The transition layer (2) forms secondary micropores inside. The outer layer (3) covers the outside of the transition layer (2). The outer layer (3) is composed of graphite and carbon nanotubes. The outer layer (3) forms tertiary micropores inside. The conductive coating (4) is coated on the surface of the outer layer (3). The conductive coating (4) is composed of conductive carbon black and binder.

2. The silicon-carbon composite anode structure with multi-level micropores according to claim 1, characterized in that: The primary micropores have a pore size of 2-5 nm, the secondary micropores have a pore size of 10-20 nm, and the tertiary micropores have a pore size of 30-50 nm, with the pore sizes of the primary, secondary, and tertiary micropores gradually increasing from the inside to the outside.

3. The silicon-carbon composite anode structure with multi-level micropores according to claim 1, characterized in that: The carbon nanotubes in the outer layer (3) intertwine to form a conductive network, and the graphite is uniformly distributed in the network formed by the carbon nanotubes.

4. The silicon-carbon composite anode structure with multi-level micropores according to claim 1, characterized in that: The core layer (1) and the transition layer (2) are tightly bonded by chemical bonds, and the transition layer (2) and the outer layer (3) are tightly bonded by chemical bonds.

5. The silicon-carbon composite anode structure with multi-level micropores according to claim 1, characterized in that: The mass percentage of amorphous carbon in the core layer (1) is 30%-50%, and the particle size of the nano-silicon particles is 50-200nm.

6. The silicon-carbon composite anode structure with multi-level micropores according to claim 1, characterized in that: The thickness of the transition layer (2) is 1-3 μm, and the thickness of the outer layer (3) is 2-5 μm.

7. The silicon-carbon composite anode structure with multi-level micropores according to claim 1, characterized in that: The thickness of the conductive coating (4) is 0.5-1 μm, and the binder is polyvinylidene fluoride or sodium carboxymethyl cellulose.

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