Negative Electrode Composition Near the Tab for Fast-Charging Li-Ion Cells
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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 charging and discharging.
Innovation Solution
A secondary battery design with a negative electrode comprising a current collector and active material layers, where the second region near the tab has a higher percentage of silicon-based material and carbon-containing material, enhancing lithium ion transport and reducing lithium plating by increasing porosity and specific surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is added to increase capacity, then the capacity of the negative electrode is improved, but lithium dendrite formation and lithium plating occur more frequently
Solution Approach 1:
The patent applies local quality by creating different active material layer compositions in different regions of the current collector. The first region (near tab) has higher carbon-containing material content to prevent lithium plating, while the second region has higher silicon-based material content to maximize capacity. This spatial differentiation resolves the contradiction between capacity and reliability.
Solution Approach 2:
The patent uses composite materials by combining silicon-based material with carbon-containing material in a layered structure. The carbon-containing material acts as a protective component that prevents lithium dendrite formation while the silicon-based material provides high capacity, thus resolving the contradiction between capacity improvement and reliability.
2Quantity of substance
If the active material layer is made thicker to increase capacity, then the capacity per unit area is improved, but the fast charging capability deteriorates due to longer lithium ion transport paths
Solution Approach 1:
The patent applies local quality by making the active material layer thinner in the first region near the tab where lithium ion transport speed is critical for fast charging, while maintaining greater thickness in the second region where capacity is prioritized. This regional differentiation resolves the contradiction between capacity and charging speed.
Solution Approach 2:
The patent resolves the contradiction by transitioning from a uniform one-dimensional thickness to a two-dimensional variable thickness structure, where thickness is optimized independently in different spatial regions. This allows simultaneous optimization of fast charging capability (thin near tab) and capacity (thick in main body).
3Ease of manufacture
If the second region near the tab is made thinner to improve manufacturing, then the manufacturing process is simplified, but the capacity of the second region decreases significantly
Solution Approach 1:
The patent applies local quality by concentrating high-capacity silicon-based material in the second region's active material layer, compensating for the reduced thickness. This ensures that despite the thinner structure facilitating manufacturing, the capacity is maintained through optimized material distribution.
Solution Approach 2:
The patent changes the compositional parameters of the active material layer in the second region by increasing the percentage of silicon-based material, which has higher specific capacity. This parameter change compensates for the reduced thickness, maintaining overall capacity while enabling simplified manufacturing.
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 fast charging capability and cycle stability by optimizing the active material composition, reducing lithium dendrite formation, and maintaining high capacity and stability across the electrode.
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 carbon-containing material includes a first carbon material, which is a fast-charging high-dynamic carbon material, so that the fast-charging capability of the second region can be improved
Data Source
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Figure 3a~3b
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AI summary
The present disclosure relates to the technical field of lithium batteries, and specifically to 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. Therefore, the capacity of the second region can be increased, the charging speed of the second region can be increased, and the precipitation of lithium dendrites in the second region can be alleviated.