Bilayer Graphite Negative Electrode for Fast-Charging Energy Density
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Solution Overview
Problem
Existing secondary batteries face a challenge in achieving both high energy density and quick-charging ability, as improvements in quick-charging ability often compromise energy density.
Innovation Solution
A negative electrode with a bilayer structure, where the upper layer consists of graphite particles with a median diameter of 4-10 µm and a BET specific surface area of 2.0-4.0 m²/g, and the upper layer's thickness is less than 5% of the total mixture layer, promoting electrolyte permeation without significantly affecting energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the negative electrode uses a bilayer structure with different graphite particle sizes to improve quick-charging ability, then the quick-charging ability is improved, but the energy density decreases
Solution Approach 1:
The negative electrode mixture layer is divided into two regions with different graphite particle size characteristics: a lower layer region closer to the current collector with larger graphite particles (D50 ≥ 10 μm) for high capacity and energy density, and an upper layer region closer to the electrolyte interface with smaller graphite particles (D50: 3 μm to 10 μm) for enhanced electrolyte permeation and quick-charging ability. This local differentiation allows each region to optimize for its specific function while maintaining overall battery performance.
2Productivity
If the upper layer thickness is increased to improve electrolyte permeation, then the quick-charging ability is improved, but the energy density significantly decreases
Solution Approach 1:
The thickness of the upper layer region is precisely controlled to be 5% to 50% of the total negative electrode mixture layer thickness. This parameter optimization ensures sufficient electrolyte permeation for quick-charging while minimizing the loss of energy density. The controlled thickness range balances the competing requirements of ion transport efficiency and active material utilization.
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 solution enhances both energy density and quick-charging ability, with the upper layer improving electrolyte permeation and reducing internal resistance, thereby achieving high energy density and excellent quick-charging performance.
Implementation Method 1
the upper layer improving electrolyte permeation
Implementation Method 2
reducing internal resistance
Data Source
Figure 1
Figure 2
AI summary
In a negative electrode for a secondary battery that is an example of an embodiment, a mixture layer contains graphite particles, and has a lower layer arranged on the core body side of the mixture layer and an upper layer arranged on the surface of the mixture layer. The average thickness of the upper layer is 5% or less than the average thickness of the mixture layer. The volume-based median diameter of graphite particles contained in the lower layer exceeds 10 µm, and the volume-based median diameter of graphite particles contained in the upper layer is 4 µm or greater and 10 µm or less. The BET specific surface area of the graphite particles contained in the lower layer exceeds 4.0 m2/g, and the BET specific surface area of the graphite particles contained in the upper layer is 2.0 m2/g or greater and 4.0 m2/g or less.