Variable Porosity Cathode Layer for Thin-Film Battery Cohesion
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Solution Overview
Problem
Conventional lithium-ion thin-film batteries face degradation and malfunction due to mechanical stresses during charging and discharging cycles, resulting in compromised cyclability and capacity, as the materials' uniform morphology and porosity lead to inadequate cohesion at interfaces.
Innovation Solution
The cathode layer is designed with variable porosity between its interface with the current collector and the electrolyte layer, allowing for enhanced cohesion and increased density in specific regions, optimizing both cyclability and capacity by modifying deposition parameters such as temperature and rate during the vapor phase deposition process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cathode layer has uniform porosity throughout its thickness, then the manufacturing process is simple, but the mechanical cohesion at interfaces is inadequate leading to degradation during charging and discharging cycles
Solution Approach 1:
The cathode layer is designed with non-uniform porosity distribution, where the porosity varies through the thickness of the layer. This local variation in porosity creates regions with different mechanical and transport properties, improving interfacial cohesion without requiring complex multi-layer structures.
Solution Approach 2:
The porosity parameter of the cathode layer is changed through its thickness, transitioning from a uniform value to a gradient or stepped distribution. This parameter change optimizes the mechanical affinity at interfaces while maintaining manufacturing feasibility through controlled deposition processes.
2Quantity of substance
If the cathode layer has high density to increase capacity, then the battery capacity increases, but the mechanical stress during cycling increases leading to degradation
Solution Approach 1:
Different regions of the cathode layer have different densities optimized for their specific functions: higher density in regions requiring capacity and lower density in regions requiring mechanical compliance. This local differentiation resolves the contradiction between capacity and cyclability.
Solution Approach 2:
The cathode layer is structured as a composite with varying porosity and density characteristics through its thickness, combining regions of high density (for capacity) with regions of appropriate porosity (for mechanical stress management), achieving both high capacity and good cyclability.
3Reliability
If the cathode layer has high porosity to reduce mechanical stress, then the cyclability improves, but the battery capacity decreases
Solution Approach 1:
High porosity is localized to specific regions of the cathode layer where mechanical compliance is needed, while other regions maintain higher density for capacity. This spatial differentiation allows the system to achieve both good cyclability and adequate capacity.
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 improves the mechanical affinity of the cathode layer with its interfaces, increasing battery capacity and cyclability while maintaining robustness, avoiding the compromises of uniform porosity in existing technologies.
Implementation Method 1
These include vapor phase deposition techniques (PVD in the English terminology), such as evaporation or sputtering
Implementation Method 2
during its charging, lithium ions move from the cathode towards the anode while, during its discharge, the lithium ions move from the anode towards the cathode
Implementation Method 3
a thin film of lithium then being deposited on the TiOS layer by a vapor phase deposition process. The lithium then naturally diffuses into the TiOS layer
Implementation Method 4
The lithium then naturally diffuses into the TiOS layer which is transformed into a LiTiOS layer
Data Source
Figure 1~6
Figure 2~3
Figure 4a~4c
AI summary
A thin layer lithium-ion battery comprising, on a substrate (20, 30), a cathode current collector layer (22, 36) and an active portion consisting of a stack of a cathode layer (23, 35) made from a material capable of inserting lithium ions, an electrolyte layer (24, 34) and an anode layer (25, 33), in which the cathode layer has, depending on the thickness of same, a variable porosity between the interface of same with the cathode current collector layer and the interface of same with the electrolyte layer, the variation in porosity being non-zero so as to improve cohesion at the two interfaces.