Lithium Battery Cathode Sea-Island Structure for Adhesion
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Solution Overview
Problem
Lithium secondary batteries used in vehicles face challenges in maintaining high adhesion strength of the positive active material in the positive active material layer without increasing the binder content, which affects battery capacity and durability, especially under extreme temperature conditions.
Innovation Solution
A positive electrode with a sea-island structure is developed, where a matrix phase containing a binder supports an aggregate phase with no binder, ensuring stable adhesion and increased active material content, along with a conductive carbonaceous coat and a polymer binder for enhanced conductivity and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the content of binder in the positive active material layer is increased to improve adhesion strength, then the adhesion strength is improved, but the capacity of the battery is reduced due to decreased content of positive active material
Solution Approach 1:
The positive active material layer is segmented into a matrix phase containing binder and an aggregate phase with substantially no binder. This segmentation allows different regions to serve different functions: the matrix phase provides adhesion and structural integrity, while the aggregate phase maximizes active material content for capacity, thereby resolving the contradiction between adhesion strength and battery capacity.
Solution Approach 2:
Different phases within the positive active material layer are given different local qualities: the matrix phase has high binder content for adhesion, while the aggregate phase has minimal binder for maximum active material density. This local differentiation allows the layer to simultaneously achieve strong adhesion and high capacity without requiring uniform binder distribution throughout.
2Reliability
If the content of binder is increased to prevent peeling of positive active material, then the durability is improved, but the percentage content of positive active material is decreased
Solution Approach 1:
The positive active material layer is divided into a matrix phase that provides structural support and adhesion with binder, and an aggregate phase that maximizes active material content with minimal binder. This segmentation ensures durability through the binder-containing matrix while preserving high active material content in the aggregate phase, resolving the contradiction between durability and active material content.
Solution Approach 2:
The binder is locally concentrated in the matrix phase where it is needed for preventing peeling and providing structural integrity, while the aggregate phase maintains high active material content with substantially no binder. This local quality differentiation allows the layer to achieve both durability and high active material content simultaneously.
3Speed
If fine particulate positive active material is used to achieve high-rate charge and discharge, then the charge and discharge rate is improved, but the adhesion strength is reduced leading to peeling
Solution Approach 1:
Fine particulate positive active material is used in the aggregate phase to enable high-rate charge and discharge, while the matrix phase containing binder provides the adhesion strength that prevents peeling. The segmentation allows fine particles to be used without requiring high binder content throughout the entire layer, thus maintaining both high rate performance and adhesion strength.
Solution Approach 2:
The fine particulate positive active material is locally placed in the aggregate phase where high surface area is needed for fast charge/discharge, while the matrix phase provides the binding function. This local quality assignment allows the fine particles to achieve high-rate performance without compromising adhesion strength, as the binder is concentrated where it is needed for prevention of peeling.
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 improves the adhesion strength and capacity of the lithium secondary battery while reducing the binder content, maintaining high durability and controlling internal resistance, suitable for high-rate charge and discharge applications.
Implementation Method 1
the positive active material particles are bound with a water-soluble polymer binder to thereby form aggregates
Implementation Method 2
obtaining improved electron conductivity of the positive active material particles by mixing carbon fiber with the particulate lithium phosphoric acid transition metal compound
Data Source
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AI summary
The lithium secondary battery positive electrode provided by the present invention has a positive electrode collector and a positive active material layer formed on the collector. The positive active material layer is composed of a matrix phase containing at least one particulate positive active material and at least one binder, and an aggregate phase dispersed in the matrix phase, constituted by aggregation of at least one particulate positive active material and containing substantially no binder.