Asymmetric Protrusions on Negative Electrode Current Collector
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Solution Overview
Problem
Lithium secondary batteries with wound electrode groups face challenges in reducing negative electrode expansion during charge, leading to uneven stress distribution and decreased charge-discharge efficiency due to dendritic lithium deposition and uneven deformation.
Innovation Solution
The battery design incorporates a negative electrode current collector with first and second surfaces, featuring protrusions that create spaces for lithium deposition, where the ratio of projected areas of protrusions on the outer surface is greater than on the inner surface, ensuring effective volume absorption and reducing pressure disparities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a negative electrode current collector with protrusions is used to reduce expansion, then charge-discharge efficiency is improved, but device complexity increases
Solution Approach 1:
The current collector is designed with protrusions only at specific locations (inner peripheral surface and outer peripheral surface) rather than uniformly across the entire surface. This localized modification provides the necessary expansion accommodation and lithium deposition guidance where it is most needed, while keeping the rest of the current collector simple and maintaining manufacturing feasibility.
Solution Approach 2:
The current collector surface is segmented into distinct regions: flat central areas for efficient lithium ion transport and protrusion-equipped peripheral areas for expansion management. The protrusions themselves are segmented as discrete elements with specific spacing, creating a modular structure that balances functionality with manufacturing simplicity.
2Stability of the object's composition
If the ratio of protrusion area on outer surface is greater than on inner surface, then stress distribution is improved, but manufacturing precision requirements increase
Solution Approach 1:
The current collector features asymmetric protrusion distribution, with the outer peripheral surface having a greater protrusion area ratio than the inner peripheral surface. This asymmetry is deliberately designed to match the asymmetric stress distribution that occurs during winding and expansion, providing better stress accommodation on the outer surface where expansion forces are greatest.
Solution Approach 2:
The design specifies parameter ranges for protrusion dimensions and spacing rather than exact values, allowing manufacturing flexibility. The protrusion height, width, and spacing are defined within acceptable ranges that maintain the required area ratio relationship without requiring ultra-precise manufacturing, thus balancing performance with manufacturability.
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 configuration reduces negative electrode expansion, enhances charge-discharge efficiency, and prevents lithium metal peeling off, thereby maintaining high discharge capacity and cycle characteristics.
Implementation Method 1
Lithium metal is deposited on the first surface and the second surface by charge
Implementation Method 2
a nonaqueous electrolyte having lithium ion conductivity
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
A lithium secondary battery includes an electrode group and a nonaqueous electrolyte having lithium ion conductivity. A negative electrode includes a negative electrode current collector. The negative electrode current collector has a first surface facing an outward direction of winding of the electrode group and a second surface facing an inward direction of the winding of the electrode group. Lithium metal is deposited on the first surface and the second surface by charge. The negative electrode further includes first protrusions protruding from the first surface and second protrusions protruding from the second surface. A ratio A1X/A1 is greater than a ratio A2X/A2. A1X is a sum of projected areas of the first protrusions on the first surface. A1 is an area of the first surface. A2X is a sum of projected areas of the second protrusions on the second surface. A2 is an area of the second surface.