Negative Electrode Thin Sections for Silicon Cell Expansion
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Solution Overview
Problem
Lithium-ion secondary cells with silicon-based negative electrodes face issues of cubical expansion leading to stress concentration, strain, and potential detachment of the active material layer, resulting in decreased energy density and rapid capacity deterioration, particularly due to the formation of Li dendrites and film formation between electrodes.
Innovation Solution
A secondary cell design where the negative electrode active material layer has a larger area than the positive electrode active material layer, with thin sections at locations not facing the positive electrode, to manage expansion and reduce stress concentration, and a method for manufacturing this cell by stacking electrodes with a separator in between and injecting electrolyte into an outer package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a depressed portion is provided on the negative electrode active material layer surface facing the positive electrode, then cell expansion is prevented, but Li dendrites grow in the depressed portion causing short circuit
Solution Approach 1:
The patent applies local quality by providing thin sections only in specific locations of the negative electrode active material layer - at the periphery and at positions not facing the positive electrode - while maintaining normal thickness in the central facing region. This localized thinning prevents cell expansion at critical areas without creating the distance gaps that would promote Li dendrite growth, thus resolving the contradiction between shape control and reliability.
2Quantity of substance
If the negative electrode active material layer has larger area than the positive electrode, then capacity is increased, but stress concentration and strain occur at the boundaries
Solution Approach 1:
The patent segments the negative electrode active material layer by introducing thin sections that divide the layer into functional zones. These thin sections act as stress relief pathways, segmenting the stress distribution and preventing concentration at the boundaries between the larger-area negative electrode and the smaller positive electrode, thereby maintaining strength while preserving capacity.
Solution Approach 2:
The patent applies local quality by providing thin sections specifically at the periphery and non-facing regions of the negative electrode, while maintaining full thickness in the central region facing the positive electrode. This localized thinning relieves stress concentration at boundaries without reducing the active material capacity in the effective electrochemical region, thus resolving the contradiction between quantity and strength.
3Quantity of substance
If silicon-based negative electrode is used, then theoretical capacity is increased, but cubical expansion causes cell deterioration
Solution Approach 1:
The patent applies local quality by providing thin sections in specific locations (periphery and non-facing regions) of the silicon-based negative electrode active material layer. This localized thinning allows the high-capacity silicon material to be used while providing stress relief pathways that accommodate cubical expansion, preventing cell deterioration in the regions where thin sections are provided while maintaining capacity in the effective electrochemical region.
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 design inhibits the decrease in energy density and improves cycle life by reducing strain and stress concentration, preventing detachment of the negative electrode active material layer, thereby maintaining higher energy density and capacity retention.
Implementation Method 1
A silicon-based negative electrode is much greater in cubical expansion resulting from Li ion insertion at a time of charging than a graphite negative electrode
Implementation Method 2
an Li ion is not removed or inserted in a part of a negative electrode that does not face a positive electrode
Data Source
AI summary
The purpose of the present invention is to provide a secondary cell in which a decrease in energy density is inhibited. In order to achieve this purpose, this secondary cell has a positive electrode in which a positive electrode active material layer is provided on a positive electrode collector, and a negative electrode in which a negative electrode active material layer is provided on a negative electrode collector; the positive electrode active material layer and the negative electrode active material layer are laminated so as to face each other with a separator interposed therebetween; the negative electrode active material layer has a greater area than the positive electrode active material layer; and a thin section is provided in at least a part of the negative electrode active material layer at a location where the negative electrode active material layer does not face the positive electrode active material layer.