Hermetically Sealed Lithium Battery Positive Electrode Assist Layer
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Solution Overview
Problem
Hermetically sealed lithium secondary batteries face challenges in rapidly and accurately operating their current-interrupt mechanisms during overcharging, particularly due to increased internal resistance and reduced gas generation when the density of the positive electrode mixture layer is high, which can lead to malfunctions and reduced battery performance.
Innovation Solution
Incorporating a positive electrode assist layer that contains electroconductive material and binder, but not positive electrode active material, adjacent to the positive electrode mixture layer, allowing the overcharge inhibitor to decompose and generate gas more efficiently, thereby triggering the current-interrupt mechanism rapidly and accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the positive electrode mixture layer is increased to improve battery capacity, then the battery capacity is improved, but the gas generation during overcharging is reduced and internal resistance increases, leading to malfunction of the current-interrupt mechanism
Solution Approach 1:
The positive electrode is divided into two distinct layers: a positive electrode mixture layer containing active material for capacity, and a positive electrode assist layer containing electroconductive material and binder but substantially no active material. This segmentation allows the assist layer to专门 function in gas generation during overcharging without compromising the capacity-providing mixture layer.
Solution Approach 2:
Different regions of the positive electrode are given different compositions and functions. The mixture layer is optimized for capacity with high active material content, while the assist layer is optimized for overcharge protection with high electroconductive material content. This local differentiation resolves the contradiction between capacity and safety.
2Productivity
If the amount of electroconductive material in the positive electrode mixture layer is increased to improve gas generation, then the gas generation is improved, but the density of the positive electrode mixture layer is reduced, leading to decline in capacity per unit volume
Solution Approach 1:
The electrode structure is segmented into two layers with different compositions. The assist layer contains high amounts of electroconductive material (5-50 mass%) to ensure rapid gas generation during overcharging, while the mixture layer maintains high active material content for capacity. This segmentation allows both high productivity in gas generation and high capacity density to coexist.
Solution Approach 2:
The solution moves from optimizing a single-layer composition to a two-layer structure, adding a new dimensional aspect to the electrode design. This allows independent optimization of gas generation properties in the assist layer and capacity properties in the mixture layer, resolving the trade-off between productivity and quantity.
3Quantity of substance
If the reaction field between the positive electrode and overcharge inhibitor is increased to improve gas production, then the gas production is improved, but the battery performance is reduced due to increased internal resistance
Solution Approach 1:
The assist layer is specifically designed with high electroconductive material content (5-50 mass%) to create an optimal local reaction field for overcharge inhibitor decomposition. This localized enhancement of reaction capability occurs only where needed for safety, while the rest of the electrode (mixture layer) maintains low resistance for performance.
Solution Approach 2:
The positive electrode assist layer acts as an intermediary structure that facilitates the reaction between the overcharge inhibitor and the electrode without being part of the main capacity-providing mixture layer. This intermediary layer provides a dedicated reaction zone that enhances gas production while isolating the performance-critical mixture layer from the resistance-increasing effects of high electroconductive material content.
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 enhances the rapid operation of the current-interrupt mechanism and improves the tolerance of the battery to overcharging, maintaining high performance and capacity even during high-current charging, making it suitable for vehicular applications.
Implementation Method 1
the overcharge inhibitor undergoes oxidative decomposition—prior to the occurrence of electrolyte decomposition—and a large amount of gas is generated as a result
Implementation Method 2
the overcharge inhibitor can produce a decomposition reaction not only at the surface of the (usual) positive electrode mixture layer, but also at the surface of the positive electrode assist layer
Data Source
AI summary
A hermetically sealed lithium secondary battery is provided which has an excellent battery performance and in which a current-interrupt mechanism operates accurately when overcharging occurs. This battery comprising an electrode assembly 80 that has a positive electrode 10. The positive electrode 10 has a positive electrode current collector 12, a positive electrode mixture layer 14 formed on the current collector, and a positive electrode assist layer 16 formed on the current collector and adjacent to the positive electrode mixture layer 14.