Nonaqueous Battery Cathode Particle Structure for Cycle Life
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face a challenge in simultaneously achieving high energy density and long life, as increasing electrode density to enhance energy density leads to electrolyte decomposition, while extending life through active material surface modification compromises load characteristics and energy density.
Innovation Solution
A nonaqueous electrolyte secondary battery design incorporating a positive electrode with lithium metal composite oxide, comprising first composite oxide particles with an average size of 50 nm to 5 μm and second composite oxide particles of 2 μm to 20 μm, where the initial charge/discharge efficiency of the positive electrode is lower than that of the negative electrode, allowing for controlled efficiency and enhanced cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If electrode density is increased to achieve high energy density, then energy density is improved, but electrolyte decomposition occurs causing deteriorated cycle characteristics
Solution Approach 1:
The patent changes the particle size parameters of the lithium metal composite oxide, specifically using primary particles of 50 nm to 5 μm and secondary particles of 2 μm to 20 μm. This parameter optimization allows the electrode to maintain high density while the controlled particle sizes prevent electrolyte decomposition, resolving the contradiction between energy density and cycle characteristics
Solution Approach 2:
The patent uses composite oxide particles formed by aggregation of primary particles, creating a hierarchical composite structure. This composite material approach enables the electrode to achieve high density packing while the composite structure prevents direct contact between electrolyte and electrode surfaces, eliminating decomposition reactions and improving cycle life
2Reliability
If surface modification of active materials is performed to extend battery life, then cycle characteristics are improved, but load characteristics are lowered and energy density decreases
Solution Approach 1:
Instead of surface modification, the patent changes the fundamental particle size parameters of the active material itself. By optimizing primary particle size (50 nm to 5 μm) and secondary particle size (2 μm to 20 μm), the patent achieves both long cycle life and high energy density without the trade-off imposed by surface coating methods
Solution Approach 2:
Rather than modifying the surface of large particles to improve stability, the patent inverts the approach by creating a hierarchical structure where small primary particles aggregate into appropriately sized secondary particles. This inversion allows the bulk material properties to provide both stability and high energy density simultaneously
Data Source
AI summary
A nonaqueous electrolyte secondary battery (10) in an example embodiment includes a positive electrode (11) having a lithium metal composite oxide, and a negative electrode (12) having graphite. The lithium metal composite oxide includes first composite oxide particles which are secondary particles formed by aggregation of primary particles having an average particle size of 50 nm to 5 μm, and second composite oxide particles which are non-aggregated particles having an average particle size of 2 μm to 20 μm. The positive electrode (11) has lower initial charge/discharge efficiency than the initial charge/discharge efficiency of the negative electrode (12).