Negative Electrode Composition Gradient for Fast-Charging Li-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries face challenges in cycle performance and fast charging capabilities, particularly in electric vehicles, due to issues like lithium dendrite formation and capacity degradation in regions near the tab during the battery preparation process.
Innovation Solution
A secondary battery design with a negative electrode structure that includes a current collector with distinct regions, where the region near the tab has a higher percentage of silicon-based material and carbon-containing material, enhancing the capacity and expansion properties to improve lithium ion transport and reduce lithium plating, while using high-dynamic carbon materials for faster charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform active material layer is used across the entire negative electrode, then the manufacturing process is simple, but the capacity per unit volume in the tab region is insufficient due to thinning during preparation
Solution Approach 1:
The patent applies local quality by dividing the negative electrode into two regions with different active material compositions. The first region (main body) contains a first active material layer with lower silicon-based material content, while the second region (tab area) contains a second active material layer with higher silicon-based material content. This compensates for the thinning effect during preparation and ensures sufficient capacity per unit volume in the tab region.
2Quantity of substance
If high-capacity silicon-based material is added to increase negative electrode capacity, then the energy density improves, but the expansion during charging and discharging increases causing structural instability
Solution Approach 1:
The patent uses local quality to concentrate silicon-based material in the second region (tab area) where higher capacity is needed, while maintaining lower silicon content in the first region (main body) where structural stability is more critical. This spatial differentiation allows the battery to achieve high overall capacity while maintaining structural integrity in regions where expansion would be most damaging.
Solution Approach 2:
The patent employs composite materials by combining silicon-based material with carbon-containing material in different proportions across different regions. The composite structure mitigates the expansion issue of silicon by incorporating carbon materials that provide structural stability, while still achieving high capacity through the silicon component in the tab region.
3Speed
If the active material layer is made thinner to reduce resistance, then the fast charging capability improves, but the capacity per unit area decreases
Solution Approach 1:
The patent applies local quality by creating a gradient in active material composition across different regions. The second region (tab area) has higher silicon-based material content which provides higher capacity per unit volume, compensating for the reduced thickness. This allows the overall electrode to maintain high capacity while the tab region specifically benefits from reduced resistance and improved fast charging capability.
4Quantity of substance
If silicon-based material content is increased in the tab region, then the capacity per unit volume improves, but the lithium plating risk increases due to higher expansion
Solution Approach 1:
The patent uses local quality to strategically place higher silicon-based material content specifically in the second region (tab area) where the geometry and current distribution characteristics differ from the main body. The carbon-containing material in the same region provides a matrix that accommodates silicon expansion, thereby mitigating lithium plating risk while maintaining high capacity per unit volume in this specific region.
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 design improves the fast charging capability and cycle stability of the battery by increasing the capacity and contact area for lithium ions, reducing lithium dendrite formation, and maintaining high stability across regions.
Implementation Method 1
the expansion coefficient of the silicon-based material is greater than that of the carbon-containing material, and by setting the percentage by weight of the silicon-based material in the second region to be higher than the percentage by weight in the first region, the expansion degree of the second active material layer in the second region is greater than the expansion degree of the first active material layer in the first region during charging and discharging, so that the porosity and the specific surface area of the second active material layer in the second region are increased more significantly
Implementation Method 2
the active material layer includes a silicon-based material and a carbon-containing material
Data Source
AI summary
A secondary battery, a preparation method therefor, and an electrical device. The secondary battery includes a negative electrode. A current collector includes a first region and a second region. The second region is close to a tab. A first active material layer is located in the first region. A second active material layer is located in the second region. The percentage by weight of the silicon-based material in the second active material layer is greater than the percentage by weight of the silicon-based material in the first active material layer. The percentage by weight of the first carbon material in the second active material layer is greater than the percentage by weight of the first carbon material in the first active material layer.