Two-Layer Positive Electrode for Fast-Charging Lithium Batteries
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Solution Overview
Problem
Existing rechargeable lithium batteries face challenges in achieving high energy density, high capacity, and rapid charging characteristics while maintaining long lifecycle and high output characteristics.
Innovation Solution
A positive electrode for rechargeable lithium batteries is designed with a two-layer structure, comprising a first positive electrode active material layer with larger secondary particles and a second positive electrode active material layer with smaller single particles, each made of lithium transition metal composite oxides, optimized for energy density and output characteristics, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer positive electrode active material is used, then the structure is simple, but the energy density and output characteristics cannot be simultaneously optimized
Solution Approach 1:
The positive electrode active material layer is segmented into two distinct layers: a first layer containing larger secondary particles (formed by agglomeration of primary particles) and a second layer containing smaller single particles. This segmentation allows each layer to contribute differently - the first layer provides high energy density while the second layer enhances output characteristics and rapid charging capability, resolving the contradiction between structural simplicity and performance optimization.
Solution Approach 2:
Different regions of the positive electrode are assigned different particle sizes and morphologies to optimize local functions. The first layer with larger secondary particles is optimized for energy storage capacity, while the second layer with smaller single particles is optimized for ion transport and output performance. This local quality differentiation enables simultaneous optimization of energy density and output characteristics without requiring a completely complex overall structure.
2Quantity of substance
If only large secondary particles are used, then the energy density is high, but the rapid charging characteristics and output characteristics deteriorate
Solution Approach 1:
The particle population is segmented into two size categories distributed across two layers. The first layer contains larger secondary particles that provide high energy density, while the second layer contains smaller single particles that facilitate rapid lithium ion diffusion and electron transport. This segmentation resolves the contradiction by assigning different particle size functions to different layers, allowing both high energy density and rapid charging characteristics to coexist.
Solution Approach 2:
The positive electrode employs a composite structure combining two types of active materials with different particle characteristics. The composite of large secondary particles and small single particles creates synergistic effects where the large particles contribute to capacity while the small particles enhance rate capability, successfully resolving the contradiction between energy density and rapid charging performance.
3Productivity
If only small single particles are used, then the output characteristics and rapid charging characteristics are improved, but the energy density decreases
Solution Approach 1:
The electrode structure is segmented into two functional layers where the second layer with small single particles optimizes output characteristics and rapid charging, while the first layer with larger secondary particles compensates for energy density. This segmentation allows each layer to specialize in its optimal function without compromising the other, resolving the contradiction between productivity and energy density.
4Quantity of substance
If a two-layer structure with different particle sizes is used, then the energy density and output characteristics are simultaneously optimized, but the manufacturing complexity increases
Solution Approach 1:
While the electrode is segmented into two layers with different particle characteristics, the segmentation is implemented in a straightforward manner that balances performance optimization with manufacturing feasibility. The two-layer structure provides sufficient performance differentiation without excessive complexity, resolving the contradiction between optimized energy density and acceptable manufacturing complexity.
Data Source
AI summary
Disclosed are a positive electrode for a rechargeable lithium battery, the positive electrode including a current collector, a first positive electrode active material layer on the current collector, and a second positive electrode active material layer on the first positive electrode active material layer. The first positive electrode active material layer includes a first positive electrode active material including a lithium transition metal composite oxide as secondary particles formed by agglomeration of a plurality of primary particles, and a second positive electrode active material including a lithium transition metal composite oxide as single particles. The second positive electrode active material layer includes a third positive electrode active material including a lithium transition metal composite oxide as secondary particles formed by agglomeration of a plurality of primary particles, and a fourth positive electrode active material including a lithium transition metal composite oxide as secondary particles.