Nonaqueous Secondary Battery Cathode Mix for Energy Density and Cycle Life
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Solution Overview
Problem
Concurrent satisfaction of high energy density and long life is challenging in nonaqueous electrolyte secondary batteries, as increasing energy density leads to electrolyte accessibility issues, while extending life through surface modification of active materials lowers load characteristics and energy density.
Innovation Solution
A nonaqueous electrolyte secondary battery design using lithium metal composite oxide with first and second composite oxide particles, where the first particles have an average size of 50 nm to 5 µm and the second particles have an average size of 2 µm to 20 µm, with the positive electrode's initial charge/discharge efficiency lower than the negative electrode's, limiting discharge capacity and enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If electrodes are increased in density to achieve high energy density, then energy density is improved, but electrolyte accessibility to electrode interior deteriorates
Solution Approach 1:
The positive electrode active material is segmented into two distinct particle size ranges: fine particles (50 nm to 5 μm) that improve electrolyte penetration and wetting, and coarse particles (2 μm to 20 μm) that increase volumetric energy density. This segmentation allows the electrode to simultaneously achieve high density and good electrolyte accessibility by combining the advantages of both particle sizes.
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:
Surface modification is applied selectively to only the fine particles (50 nm to 5 μm) of the positive electrode active material, while the coarse particles (2 μm to 20 μm) remain unmodified. This local quality approach allows the fine particles to provide improved cycle characteristics through surface modification, while the coarse particles maintain high volumetric energy density and good load characteristics.
Data Source
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Figure 4~5(b)
AI summary
A nonaqueous electrolyte secondary battery (10) according to one embodiment of the present invention is provided with a positive electrode (11) that comprises a lithium metal composite oxide and a negative electrode (12) that comprises graphite. The lithium metal composite oxide contains first composite oxide particles, which are secondary particles wherein primary particles having an average particle diameter of from 50 nm to 5 µm aggregate, and second composite oxide particles, which are non-aggregated particles having an average particle diameter of from 2 µm to 20 µm. The initial charge/discharge efficiency of the positive electrode (11) is lower than the initial charge/discharge efficiency of the negative electrode (12).