Silicon-Based Negative Electrode with CNT Bundles for Conductivity Retention
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Solution Overview
Problem
Conventional lithium secondary batteries using silicon-based active materials face issues with conductivity loss due to breakage of single-walled carbon nanotubes from volume expansion, leading to reduced battery capacity and life characteristics.
Innovation Solution
A negative electrode with a carbon nanotube structure formed by bonding 2 to 5,000 single-walled carbon nanotube units side by side, prepared using a homogenizer to maintain conductivity despite volume changes, combined with a silicon-based active material SiOx (0≤x<2) and a small amount of 0.01 wt % to 1.0 wt % carbon nanotube structure in the electrode active material layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-walled carbon nanotubes are used as conductive agent in silicon-based negative electrode, then conductivity is improved, but carbon nanotubes break due to volume expansion during charge-discharge cycles
Solution Approach 1:
The conductive agent is segmented into multiple functional components: bundle-type single-walled carbon nanotubes provide initial conductivity, while silicon carbide particles fill the spaces between them. This segmentation allows each component to perform its specific function - the nanotubes maintain conductive pathways while the silicon carbide provides structural support during volume expansion.
Solution Approach 2:
A composite conductive system is created by combining bundle-type single-walled carbon nanotubes with silicon carbide particles. The silicon carbide, having similar thermal expansion properties to silicon-based active material, forms a stable matrix that prevents nanotube breakage during charge-discharge cycles while maintaining electrical conductivity through the nanotube network.
2Quantity of substance
If silicon-based active material is used to improve battery capacity, then energy density increases, but excessive volume expansion occurs during charge-discharge
Solution Approach 1:
The invention changes the physical and chemical parameters of the electrode structure by incorporating silicon carbide particles with specific properties (similar thermal expansion coefficient to silicon). This parameter matching allows the electrode to accommodate volume changes of silicon-based active material without structural degradation, enabling high capacity operation.
Solution Approach 2:
Silicon carbide particles act as an intermediary material between the silicon-based active material and the conductive agent. This intermediary provides a stable matrix that mediates the volume expansion stress, preventing direct mechanical damage to the carbon nanotube network while allowing the silicon-based material to achieve its high capacity potential.
3Reliability
If conventional conductive agents are used, then manufacturing is simple, but conductivity is insufficient for high-capacity silicon-based electrodes
Solution Approach 1:
The bundle-type single-walled carbon nanotubes are pre-formed and dispersed in the electrode slurry before electrode fabrication. This preliminary dispersion action ensures uniform distribution of the conductive agent throughout the electrode matrix, avoiding aggregation issues and ensuring consistent conductivity without requiring complex post-processing steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution maintains a conductive network, enhancing battery capacity and life characteristics by preventing carbon nanotube breakage and ensuring stable conductivity even with excessive volume changes of the silicon-based active material.
Implementation Method 1
dispersing the bundle-type single-walled carbon nanotubes by applying a shear force to the mixed solution by a homogenizer
Data Source
AI summary
A negative electrode includes a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active material and a conductive agent, wherein the negative electrode active material includes a silicon-based active material, the silicon-based active material includes SiOx (0≤x<2), the conductive agent includes a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded side by side, and the carbon nanotube structure is included in an amount of 0.01 wt % to 1.0 wt % in the negative electrode active material layer. A secondary battery including the negative electrode, and a method of preparing same are also provided.