Li-Ion Battery Electrode Porosity Control Using PVDF Electric Fields
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Solution Overview
Problem
The high compression process in lithium-ion battery electrode production leads to reduced porosity, especially on the surface, which hinders lithium ion storage and causes lithium plating, resulting in shortened battery lifespan and impaired electrochemical performance.
Innovation Solution
The use of PVDF as a binder with piezoelectric properties, where an external electrical field is applied to align and deform PVDF molecular chains, increasing porosity and density, allowing for controlled porosity adjustment during the Kalandrier process to enhance electrolyte wetting and lithium transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If high compression force is applied during calendering to increase density, then volumetric energy density increases, but porosity decreases more rapidly at the layer surface causing lithium plating
Solution Approach 1:
The patent applies different compression forces to different regions of the active material layer. The support structure provides localized mechanical support at the layer surface, enabling lower compression force in this region while maintaining higher compression force near the current collector foil. This gradient compression approach maintains surface porosity to prevent lithium plating while achieving sufficient overall density.
2Volume of stationary object
If high compression force is applied during calendering to increase density, then conductivity increases, but cracks form in the active material due to stress concentration
Solution Approach 1:
The support structure creates a gradient in mechanical properties throughout the active material layer thickness. By providing localized support, it distributes stress more evenly during compression, preventing stress concentration that would otherwise cause cracks. This enables achieving high density without compromising structural integrity.
3Volume of stationary object
If porosity is reduced to increase density, then volumetric energy density increases, but electrolyte wetting is impaired and lithium ion transfer is hindered
Solution Approach 1:
The patent creates a spatial gradient in porosity distribution throughout the active material layer. The support structure maintains higher porosity regions near the layer surface to ensure adequate electrolyte wetting and lithium ion transfer, while allowing lower porosity (higher density) regions closer to the current collector foil to maximize volumetric energy density.
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
This approach maintains high density and porosity, improving volumetric energy density and conductivity, while preventing lithium plating and extending battery lifespan by optimizing pore structure and electrolyte interface areas.
Implementation Method 1
PVDF as a binder with piezoelectric properties, where an external electrical field is applied to align and deform PVDF molecular chains
Data Source
Figure 1~2a
Figure 2b~3b
Figure 3c~4
AI summary
The invention relates to a method for manufacturing an electrode (K) for a lithium-ion battery cell, which is composed of a current collector foil (1) with an active material coated on one or both sides, containing PVDF as a binder. According to the invention, the method for adjusting the porosity of the active material layer (2) coated on the current collector foil (1) comprises at least one process step in which at least one external electric field is applied, which utilizes the dipolarity of PVDF such that the PVDF molecular chains contract, reducing porosity, or expand, increasing porosity.