Two-Layer Positive Electrode for Lithium Battery
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Solution Overview
Problem
Rechargeable lithium ion batteries face challenges in improving both the flexibility and cycle-life characteristics of their positive active material layers, as increasing the thickness of the positive active material layer to enhance capacity and cycle characteristics often results in reduced flexibility, leading to potential damage during manufacturing, and using low elastic modulus binders to maintain flexibility compromises cycle characteristics.
Innovation Solution
A positive electrode with a two-layered structure comprising a high elastic modulus layer and a low elastic modulus layer, where the high elastic modulus layer is bonded with a conductive material and a binder having a tensile modulus of 400 MPa to 1200 MPa, and the low elastic modulus layer is bonded with a binder having a tensile modulus of 150 MPa to 700 MPa, allowing for improved flexibility and cycle-life characteristics while maintaining capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the positive active material layer is made thicker to enhance capacity and cycle characteristics, then the cycle characteristics are improved, but the flexibility of the positive active material layer is deteriorated
Solution Approach 1:
The positive active material layer is divided into two distinct layers: a first positive active material layer with high density and high elastic modulus binder, and a second positive active material layer with lower density and low elastic modulus binder. This segmentation allows each layer to fulfill different functions - the first layer provides cycle stability while the second layer ensures flexibility, resolving the contradiction between cycle characteristics and flexibility.
Solution Approach 2:
Different regions of the positive active material layer are assigned different properties through the use of two layers with distinct characteristics. The first layer (near current collector) has high elastic modulus for structural stability, while the second layer (outer layer) has low elastic modulus for flexibility. This local differentiation of material properties enables simultaneous achievement of cycle life and flexibility.
2Ease of operation
If a low elastic modulus binder is used to maintain flexibility, then the flexibility of the positive active material layer is improved, but the cycle characteristics of the rechargeable lithium ion battery are deteriorated
Solution Approach 1:
The binder system is segmented into two types with different elastic moduli, each used in a specific layer. The high elastic modulus binder is used in the first layer to ensure cycle stability, while the low elastic modulus binder is used in the second layer to provide flexibility. This segmentation of binder functions resolves the contradiction between flexibility and cycle characteristics.
Solution Approach 2:
Different binder materials with specific elastic modulus properties are locally assigned to different layers. The high elastic modulus binder (400-1200 MPa) is placed in the first layer where structural stability is critical, while the low elastic modulus binder (150-700 MPa) is placed in the second layer where flexibility is prioritized. This local optimization of binder properties simultaneously achieves both flexibility and cycle life.
Data Source
AI summary
A positive electrode for a rechargeable lithium battery includes a positive current collector; a high elastic modulus layer on the positive current collector and including a first positive active material and a high elastic modulus binder; and a low elastic modulus layer on the high elastic modulus layer and including a second positive active material and a low elastic modulus binder, wherein the low elastic modulus binder has a lower tensile modulus than the high elastic modulus binder. A winding element includes the positive electrode. A rechargeable lithium battery includes the winding element.