Layered Negative Electrode for Li-Ion Battery
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Solution Overview
Problem
Lithium ion secondary batteries using uniformly mixed graphite and low-temperature carbonized coke as negative active material particles fail to achieve both low internal resistance and high capacity retention rate after a low-temperature pulse cycle test, as they do not sufficiently leverage the advantages of either material alone.
Innovation Solution
A lithium ion secondary battery design featuring a negative active material layer with a higher ratio of graphite near the current collector for low internal resistance and a higher ratio of amorphous carbon near the surface for high capacity retention, formed in a layered structure with specific density ranges to optimize lithium ion transfer and prevent metal lithium deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a layered structure with different particle distributions is used, then both low internal resistance and high capacity retention rate are achieved, but the manufacturing complexity increases
Solution Approach 1:
The patent uses parameter changes by controlling the radial distribution of particle types and sizes during the coating process. By adjusting coating conditions to achieve the desired particle distribution pattern, the complex layered structure is formed through process parameters rather than complex manufacturing steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The battery achieves low internal resistance comparable to one using only graphite and high capacity retention rate comparable to one using only amorphous carbon, while maintaining a simple layer structure for easy manufacturing and stable performance under high current and low temperature conditions.
Implementation Method 1
graphite has anisotropy and thus portions for insertion/extraction of lithium ions are biased outward as compared with isotropic low-temperature carbonized coke. Accordingly, as compared with the low-temperature carbonized coke, transfer (outgoing and ingoing) of lithium ions in graphite
Implementation Method 2
transfer (outgoing and ingoing) of lithium ions in graphite (extraction of lithium ions from the inside and insertion (intercalation) of lithium ions into the inside)
Data Source
AI summary
A lithium ion secondary battery involves a negative electrode sheet including a negative current collector and a negative active material layer that contains negative active material particles including first particles and second particles. In the negative active material layer, the ratio of the first particles to the total negative active material particles in a part on the current collector side in the layer thickness direction of the negative active material layer is higher than the ratio of the first particles to the total negative active material particles in the whole negative active material layer and the ratio of the second particles to the total negative active material particles in a part on an outer surface side of the negative active material layer in the layer thickness direction is higher than the ratio of the second particles to the total negative active material particles in the whole negative active material layer.