Bimodal Negative Electrode Active Material for Fast-Charging Batteries
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Solution Overview
Problem
Lithium secondary batteries face limitations in capacity and output due to the use of graphite as a negative electrode material, which has a small interlayer distance, few lithium ion sites, and a plate-like structure leading to slow intercalation rates and low packing density, necessitating a solution for improved rapid charging and lifespan characteristics without compromising electrode density.
Innovation Solution
A negative electrode with a multilayer structure featuring a first active material layer and a second bimodal active material layer with different specific surface areas, where the second active material has a larger specific surface area, enhancing capacity and adhesion between the active materials, and including silicon oxide-based materials to maximize chargeable characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If graphite is used as negative electrode material, then the battery has long service lifespan and relatively low price, but the capacity is restricted to 372 mAh/g and output characteristics are not satisfied
Solution Approach 1:
The patent uses a composite negative electrode structure combining graphite (first active material) with silicon oxide or silicon-carbon composite (second active material). This composite approach allows the electrode to achieve capacity beyond the 372 mAh/g limitation of pure graphite while maintaining structural stability and long cycle life through the synergistic properties of both materials.
2Duration of action of stationary object
If graphite with plate-like structure is used, then the battery has long service lifespan, but the intercalation rate of lithium ions is slow and high output characteristics are not satisfied
Solution Approach 1:
The patent applies local quality by creating a heterogeneous electrode structure where different regions have different functions: graphite provides structural stability and long lifespan, while silicon oxide/silicon-carbon regions provide high capacity and improved lithium ion insertion/extraction sites. The bimodal particle size distribution further optimizes this by having smaller particles for fast ion transport and larger particles for structural integrity.
3Productivity
If the specific surface area of active material is increased to improve rapid charging characteristics, then the charging rate is improved, but the electrode density decreases
Solution Approach 1:
The patent changes the parameter of specific surface area distribution by using bimodal active material with two distinct size ranges. The smaller particles (higher specific surface area) provide numerous sites for rapid lithium ion insertion and improve charging characteristics, while the larger particles (lower specific surface area) maintain high packing density and electrode volume utilization. This parameter distribution optimization resolves the contradiction between fast charging and high density.
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 bimodal active material structure improves rapid charging capabilities and cycle stability by maintaining high electrode density and adhesion, even under rapid charging conditions, resulting in enhanced capacity retention and extended lifespan.
Implementation Method 1
the graphite has a very small interlayer distance of 0.335 nm, has few sites for lithium ions to be intercalated, and has a long diffusion distance through a graphite basal plane is long
Implementation Method 2
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
Data Source
AI summary
A negative electrode for a secondary battery includes: a current collector; a first electrode negative 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. The second active material is a bimodal active material including active materials having different specific surface areas, a specific surface area (B2) of the second active material is larger than a specific surface area (B1) of the first active material, and the specific surface area of the second active material is an average specific surface area of an active material (2-1-th active material) having a large specific surface area and an active material (2-2-th active material) having a small specific surface area.