Multi-Layer Silicon Anode Structure for Conductivity and Surface Stability
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Solution Overview
Problem
The use of silicon-based active materials in secondary batteries leads to electrode surface defects due to volume contraction and expansion, reducing solids content and causing migration phenomena of conductive agents and binders, resulting in increased resistance and deteriorated adhesive properties.
Innovation Solution
A multi-layer anode structure is developed with varying contents and types of carbon nanotubes, including single-walled, thin-walled, and multi-walled carbon nanotubes, to maintain conductivity and increase solids content, preventing electrode surface defects and migration phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon nanotubes are added as a conductive agent to maintain conductivity during silicon-based active material volume changes, then conductivity is improved, but solids content in the slurry is reduced
Solution Approach 1:
The anode is divided into multiple layers with different compositions and functions. The first layer contains silicon-based active material with conductive agent for high conductivity, while the second layer contains carbon-based active material without conductive agent to maintain high solids content, preventing migration phenomena during drying
Solution Approach 2:
Different regions of the anode are assigned different properties: the first layer near the current collector has high conductive agent content to ensure electron transport during silicon expansion/contraction, while the second layer has high solids content to prevent binder and conductive agent migration to the surface
2Reliability
If carbon nanotubes are pre-dispersed to improve conductivity, then conductivity is improved, but the process complexity increases and solids content is reduced
Solution Approach 1:
The conductive agent is segmented and placed only in the first layer where it is needed for conductivity, while the second layer uses only carbon-based active material. This eliminates the need for complex pre-dispersion processes for the entire anode structure
Solution Approach 2:
The conductive agent is extracted from the second layer entirely, which eliminates the migration problem and simplifies the manufacturing process for that layer, requiring only mixing of carbon-based active material with binder
3Quantity of substance
If silicon-based active material is used to increase capacity and energy density, then energy density is improved, but volume contraction and expansion occurs causing conductive path destruction
Solution Approach 1:
The anode is divided into a first layer containing silicon-based active material that provides high capacity, and a second layer with carbon-based active material that provides structural stability. This segmentation allows the silicon layer to expand and contract while the carbon layer maintains overall structural integrity and conductive paths
Solution Approach 2:
The anode uses a composite structure combining silicon-based active material in the first layer with carbon-based active material in the second layer. The silicon provides high capacity while the carbon provides structural stability, creating a composite system that leverages the advantages of both materials
Data Source
AI summary
The present disclosure provides an anode for a secondary battery, the anode including: an anode current collector; a first anode mixture layer provided on at least one surface of the anode current collector; a second anode mixture layer provided on the first anode mixture layer; and a third anode mixture layer provided on the second anode mixture layer, wherein each of the anode mixture layers includes a Si-containing anode active material and carbon nanotubes, and the number of walls of each of first carbon nanotubes included in the first anode mixture layer, second carbon nanotubes included in the second anode mixture layer, and third carbon nanotubes included in the third anode mixture layer satisfies a relation of [first carbon nanotubes<second carbon nanotubes<third carbon nanotubes].