Asymmetric Electrode Design for Lithium Battery Alignment
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Solution Overview
Problem
Lithium secondary batteries face issues with distorted electrode shapes during manufacturing, leading to misalignment of positive and negative electrode mixture layers, which results in reduced capacity, lifetime, and potential internal short circuits due to nonuniform reaction and lithium dendrite formation during high current charge and discharge.
Innovation Solution
The battery design ensures that the active material mixture layer-free portion is arranged at one end of the electrode, with a larger negative electrode mixture layer width compared to the positive electrode, and a specific ratio of deviations between the edges of these layers, allowing for effective alignment and controlled lithium supply to prevent dendrite formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the active material mixture layer-free portion is arranged at one end side in the width direction to enable large current charge and discharge, then the current collecting efficiency is improved, but the electrode shape becomes distorted causing misalignment of mixture layers
Solution Approach 1:
The invention applies local quality by creating an asymmetric electrode structure where the active material mixture layer-free portion is positioned only at one end side in the width direction of the metal foil. This localized modification enables improved current collection at the collector end while maintaining the active material layers in the discharge area, thus resolving the contradiction between current collecting efficiency and alignment precision.
Solution Approach 2:
The invention employs asymmetry by arranging the active material mixture layer-free portion asymmetrically at one end of the electrode rather than symmetrically at both ends or in the center. This asymmetric configuration optimizes the current collection path while minimizing distortion-induced misalignment, as the asymmetric design allows for better control of electrode shape during manufacturing.
2Manufacturing precision
If the electrode is subjected to press working for adjusting density of active material mixture layer, then the density is improved, but the metal foil portion without active material mixture layer is not rolled causing shape distortion
Solution Approach 1:
The invention applies segmentation by dividing the metal foil into two functional zones: an active material mixture layer portion that undergoes press working for density adjustment, and an active material mixture layer-free portion that serves as the current collector. This segmentation allows differential treatment of the two zones during manufacturing, enabling density optimization without causing shape distortion in the collector region.
3Reliability
If the positive and negative electrode mixture layers are not opposed to each other via separator, then the charge and discharge reaction cannot proceed at those positions, but the excessive reaction at other positions leads to capacity reduction and lifetime degradation
Solution Approach 1:
The invention applies parameter changes by precisely controlling the width and position parameters of the active material mixture layer-free portion relative to the active material mixture layer portion. By adjusting these geometric parameters, the invention ensures proper alignment and opposition of the positive and negative electrode mixture layers via the separator, achieving uniform reaction distribution and preventing both under-reaction and excessive reaction zones, thus improving reliability and extending battery lifetime.
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 enables large current charge and discharge with excellent charge and discharge characteristics and high safety, preventing internal short circuits and maintaining battery performance over time.
Implementation Method 1
a separator interposing between the both electrodes
Implementation Method 2
positions where the positive electrode mixture layer and the negative electrode mixture layer are not opposed to each other via the separator... difficult to be subjected to the charge and discharge reaction
Data Source
AI summary
In a lithium secondary battery, the electrode assembly includes a positive electrode and a negative electrode which are assembled together with a separator interposing between said both electrodes. Each of the electrodes includes an active material mixture layer portion and an active material mixture layer free-portion which are arranged on a surface of said metal foil. A relationship of B1<B2 is satisfied, and a value of (A1+A2)/(B2−B1) is set equal to or less than 4. Where B1 (mm) is a width of the active material mixture layer portion of the positive electrode; B2 (mm) is a width of the active material mixture layer portion of the negative electrode; and each of A1 (mm) in the positive electrode and A2 (mm) in the negative electrode is a deviation between a straight line linking both corners of the active material mixture layer-free portion in the length direction of the metal foil and an edge of the active material mixture layer-free portion at a middle point in the length direction of the metal foil.