Bimodal Negative Electrode Structure for Fast-Charging Li-Ion Batteries
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Solution Overview
Problem
Existing negative electrodes for lithium secondary batteries face challenges in achieving high capacity, rapid charging characteristics, and stable lifespan due to limitations in intercalation rate, packing density, and adhesion between the current collector and active material layer, particularly under rapid charging conditions.
Innovation Solution
A negative electrode with a multilayer structure comprising a first and second active material layer, where the second layer includes a bimodal active material with smaller particles, enhancing adhesion and allowing for high rolling density and improved lithium ion mobility, while incorporating silicon oxide-based materials to maximize chargeable characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite is used as negative electrode material, then low price and long service lifespan are achieved, but capacity is limited to 372 mAh/g due to small interlayer distance and few lithium ion sites
Solution Approach 1:
The patent uses a composite structure combining graphite particles with silicon oxide-based active material. The silicon oxide component provides additional lithium ion intercalation sites beyond the graphite's limited capacity, achieving overall capacity greater than 372 mAh/g while maintaining the structural stability of graphite.
Solution Approach 2:
The patent modifies the particle size parameters of graphite, using a bimodal distribution with D50 of 10-20 μm and D90 of 20-40 μm. This parameter optimization improves packing density and lithium ion diffusion characteristics, enhancing both capacity and rate performance.
2Productivity
If graphite with plate-like structure is used, then long service lifespan is achieved, but packing density is low and particle orientation is poor leading to slow intercalation rate
Solution Approach 1:
The patent optimizes graphite particle size parameters (D50: 10-20 μm, D90: 20-40 μm) and uses a bimodal size distribution to improve packing density. The controlled particle size reduction increases the number of intercalation sites accessible to lithium ions, enhancing the intercalation rate while maintaining adequate packing density.
Solution Approach 2:
The composite structure with silicon oxide-based material compensates for the slow intercalation kinetics of graphite. The silicon oxide component provides alternative pathways for lithium ion insertion, improving overall rate performance without requiring changes to the graphite's inherent plate-like structure.
3Power
If rapid charging is performed, then high output is achieved, but adhesion between negative electrode active material and current collector decreases
Solution Approach 1:
The patent uses a composite structure where silicon oxide-based active material is combined with graphite. The silicon oxide component has better dimensional stability during rapid lithium ion insertion/extraction, reducing mechanical stress and delamination at the electrode-current collector interface during rapid charging.
Solution Approach 2:
The optimized graphite particle size (D50: 10-20 μm) and bimodal distribution improve the mechanical integrity of the electrode structure. The smaller particles reduce internal stress concentration, while the controlled size distribution maintains adequate packing, both contributing to improved adhesion under rapid charging conditions.
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 electrode achieves excellent rapid charging capabilities and stable cycle characteristics with high capacity retention rates, even under high current conditions, by maintaining electrode density and improving adhesion between the active material and current collector.
Implementation Method 1
a lithium secondary battery having a high energy density and voltage, a long cycle lifespan, and a low discharge rate has been widely used. The lithium secondary battery is a secondary battery that includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator, and an electrolyte and is charged and discharged by intercalation-desorption of lithium ions.
Implementation Method 2
Another embodiment of the present invention is directed to providing a negative electrode having stable lifespan characteristics without generating a decrease in adhesion between a current collector and a negative electrode active material layer even under a rapid charging condition.
Data Source
AI summary
A negative electrode for a secondary battery includes: a current collector; a first negative electrode active material layer formed on the current collector and containing a first active material; and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second active material, wherein the second active material is a bimodal active material including small particles and large particles having different particle sizes, a particle size (D2) of the second active material is smaller than a particle size (Dl) of the first active material, and the particle size of the second active material is an average particle size of the small particles and the large particles.