Layered Li-Ion Battery Anode to Limit Alloy Expansion Gaps
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Solution Overview
Problem
The reduction of charge/discharge cycle characteristic in lithium ion secondary batteries using alloying materials as negative electrode active materials is often problematic due to large volume changes during charging and discharging, leading to inter-particle gaps and isolation of active material particles from the conductive path.
Innovation Solution
A negative electrode design with a specific layering structure where graphite particles with low internal porosity (≤10%) and alloying materials are predominantly in the surface layer, while higher porosity graphite particles (>10%) are in the inner layer, maintaining adhesiveness and reducing inter-particle gaps, thus improving cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If alloying material is used as negative electrode active material to increase lithium ion capacity, then the amount of lithium ions occluded per unit volume increases, but volume change during charging and discharging causes inter-particle gaps and particle isolation
Solution Approach 1:
The patent applies local quality by creating a layered structure where different types of graphite particles are distributed at different positions: low-porosity graphite particles are concentrated in the second layer (farther from current collector) while high-porosity graphite particles are concentrated in the first layer (closer to current collector). This spatial differentiation optimizes each region's function to collectively suppress volume change effects.
Solution Approach 2:
The patent segments the graphite particle population into two distinct groups based on internal porosity characteristics. By dividing the graphite particles into low-porosity and high-porosity categories and strategically distributing them across different layers, the patent addresses volume change issues through segmented functional zones rather than treating all particles uniformly.
2Use of energy by moving object
If alloying material is used to increase capacity, then energy storage increases, but structural integrity deteriorates due to large volume change
Solution Approach 1:
The patent employs composite materials by combining alloying material with two types of graphite particles having different porosity characteristics. This composite structure leverages the high capacity of alloying material while using the graphite particles with different porosities to provide structural support and maintain integrity during volume changes.
Solution Approach 2:
The patent applies beforehand cushioning by using high-porosity graphite particles in the first layer (closer to current collector) to absorb and cushion the volume expansion effects before they propagate through the electrode structure. This pre-positioned cushioning layer protects the overall structural integrity during charging cycles.
3Ease of manufacture
If uniform distribution of active materials is used to simplify manufacturing, then ease of manufacture increases, but charge/discharge cycle characteristic deteriorates due to inter-particle gap formation
Solution Approach 1:
The patent implements local quality by specifying different particle type distributions for different layers. Rather than uniform distribution, the first layer is enriched with high-porosity graphite particles while the second layer is enriched with low-porosity graphite particles and alloying material, optimizing each layer's local properties for its specific function.
Solution Approach 2:
The patent transitions from a one-dimensional uniform mixture to a two-dimensional layered structure with vertical stratification. By introducing the layering dimension, the patent achieves better performance control while maintaining manufacturing feasibility through sequential coating or mixing processes that can create layered architectures.
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
This design effectively suppresses the formation of inter-particle gaps and detachment of active material particles, enhancing the charge/discharge cycle characteristic of the battery by maintaining a stable conductive path and structural integrity.
Implementation Method 1
an alloying material which alloys with lithium
Implementation Method 2
graphite particles having a particle internal porosity of 10% or lower, graphite particles having a particle internal porosity of greater than 10%
Implementation Method 3
reduction of charge/discharge cycle characteristic is often problematic. This is considered be caused by a large volume change of the alloying material due to charging and discharging
Data Source
Figure 1~2
Figure 3
AI summary
A negative electrode for lithium ion secondary batteries according to the present invention is provided with a negative electrode collector and a negative electrode mixture layer that is formed on the negative electrode collector; the negative electrode mixture layer comprises a negative electrode active material which contains graphite particles A that have an internal porosity of 10% or less, graphite particles B that have an internal porosity of more than 10%, and an alloying material that is alloyed with lithium; the negative electrode mixture layer comprises a first layer that is formed on the negative electrode collector and a second layer that is formed on the first layer; the amounts of the graphite particles A and the alloying material contained in the second layer are higher than those contained in the first layer; the amount of the graphite particles B contained in the firs layer is higher than that contained in the second layer; and the content of the alloying material is 15% by mass or less relative to the total amount of the negative electrode active material in the negative electrode mixture layer.