Silicon Negative Electrode Dual-Layer Structure for CNT Stability
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Solution Overview
Problem
Existing negative electrodes in lithium secondary batteries face challenges in maintaining conductivity and adhesion due to the breakage of single-walled carbon nanotubes during repeated charge and discharge cycles, especially when using silicon-based active materials that undergo significant volume expansion.
Innovation Solution
A negative electrode design featuring a dual-layer structure, where a first negative electrode active material layer is coated on a collector, followed by a second layer containing a silicon-based active material and a carbon nanotube structure. The carbon nanotube structure, composed of 2 to 5,000 single-walled carbon nanotube units bonded side by side, is included in an amount of 0.01 wt % to 1.0 wt % in the second layer, enhancing conductivity and adhesion while minimizing the migration of binder and conductive agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-walled carbon nanotubes are used as conductive agent in silicon-based negative electrode, then electrical conductivity is improved, but the carbon nanotubes break during repeated charge and discharge cycles due to volume expansion, degrading life characteristics
Solution Approach 1:
The negative electrode is divided into two distinct layers: a first negative electrode active material layer containing graphite and a second negative electrode active material layer containing silicon-based active material. This segmentation isolates the silicon-based material's volume expansion to the second layer, preventing damage to the carbon nanotube network in the first layer while maintaining conductivity in the silicon-containing layer.
Solution Approach 2:
The carbon nanotube structure is specifically concentrated in the second negative electrode active material layer that contains the silicon-based active material. This local placement ensures that the conductive network is positioned exactly where it is needed to maintain conductivity during silicon's volume expansion, while the first layer provides a stable structural foundation.
2Stability of the object's composition
If carbon nanotube dispersion with low solid content is used to uniformly arrange carbon nanotubes, then uniform distribution is achieved, but negative electrode adhesion and electrical conductivity are significantly reduced due to binder and conductive agent migration
Solution Approach 1:
The electrode is segmented into two layers with different compositions and functions. The first layer uses a dispersion with higher solid content to ensure strong adhesion and conductivity, while the second layer uses a dispersion with lower solid content to achieve uniform carbon nanotube distribution. This segmentation allows each layer to optimize its dispersion characteristics without compromising the other.
Solution Approach 2:
The first negative electrode active material layer acts as an intermediary layer between the current collector and the second layer. It provides a stable foundation with strong adhesion and conductivity, allowing the second layer to use lower solid content dispersion for uniform carbon nanotube arrangement without suffering from binder and conductive agent migration issues.
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 dual-layer structure effectively maintains a conductive network even with large volume changes of the silicon-based active material, reduces the migration of binder and conductive agents, and enhances the adhesion between layers, leading to improved input/output characteristics and life characteristics of the battery.
Implementation Method 1
the second negative electrode active material layer includes a second negative electrode active material and a second conductive agent, wherein the second negative electrode active material includes a silicon-based active material... conductivity in a negative electrode active material layer is improved due to its thin and elongated shape
Implementation Method 2
since a volume of the silicon-based active material excessively expands due to charge and discharge of the battery
Implementation Method 3
there is a problem in that negative electrode adhesion and electrical conductivity are significantly reduced due to the occurrence of a migration phenomenon in which a binder and the conductive agent, which have relatively lower density than the negative electrode active material, easily move to an upper portion of the negative electrode active material layer
Data Source
AI summary
The present invention relates to a negative electrode including a negative electrode collector, a first negative electrode active material layer disposed on the negative electrode collector, and a second negative electrode active material layer disposed on the first negative electrode active material layer, wherein the second negative electrode active material layer includes a second negative electrode active material and a second conductive agent, wherein the second negative electrode active material includes a silicon-based active material, the silicon-based active material includes SiOx (0≤x<2), the second 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 second negative electrode active material layer, and a secondary battery including the same.