Double-Layer Cathode Structure for Nail-Piercing-Resistant Li-Ion Cells
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Solution Overview
Problem
Lithium ion batteries face safety issues due to external force-induced internal short circuits, which current methods address by reducing energy density, necessitating a solution that enhances safety performance while maintaining high energy density.
Innovation Solution
The implementation of a cathode with a double-layer structure and an insulating layer in the uncovered regions of the cathode current collector, combining a first cathode active material layer with a smaller particle size and high binder content, and a second cathode active material layer with normal binder content, along with an insulating layer on the uncovered foil regions, to prevent short circuits during nail piercing tests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the energy density of lithium ion batteries is reduced to improve safety, then safety performance is improved, but battery performance deteriorates
Solution Approach 1:
The cathode is divided into two distinct layers: a first cathode active material layer with smaller particles and high binder content for safety, and a second cathode active material layer with normal binder content for energy density. This segmentation allows each layer to perform its specialized function without compromise.
Solution Approach 2:
Different regions of the cathode are given different properties: the first layer uses small particles (0.2-15 μm) and high binder content (5-20 wt%) for short-circuit resistance, while the second layer uses normal particle sizes and binder content for energy storage. The insulating layer is applied selectively to uncovered foil regions.
2Reliability
If a double-layer cathode structure with insulating layer is added, then safety performance is improved, but device complexity increases
Solution Approach 1:
The safety function is merged into the cathode structure itself through the dual-layer design, where the first layer with high binder content and small particles provides inherent short-circuit resistance. The insulating layer on uncovered regions further merges protection directly into the cathode assembly.
Solution Approach 2:
The cathode employs a composite structure combining two different active material layers with distinct compositions and properties. The first layer contains small particles (0.2-15 μm) and high binder content (5-20 wt%), while the second layer has normal characteristics, creating a composite material system that delivers both safety and performance.
Data Source
AI summary
An electrochemical device includes a cathode, a separator and an anode. The cathode includes a cathode current collector, a first cathode active material layer including a first cathode active material, a second cathode active material layer including a second cathode active material, and an insulating layer. The first cathode active material layer is disposed between the cathode current collector and the second cathode active material layer, and the first cathode active material layer is disposed on a first region of a surface of the cathode current collector facing an anode active material layer of the anode, and the thickness of the first cathode active material layer is greater than Dv50 of the first cathode active material. The insulating layer is disposed on a second region of the surface of the cathode current collector not facing the anode active material layer of the anode.