Graphite Anode Composition for High-Rate Cycling and Low Expansion
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high power characteristics, cycle life, and reduced volume expansion, particularly due to limitations in the negative active material's ability to facilitate rapid charging and discharging while minimizing resistance and volume changes during charge and discharge cycles.
Innovation Solution
A negative active material is developed comprising tertiary particles of natural graphite with secondary particles agglomerated and spheroidized, artificial graphite on the surface, and an amorphous carbon coating layer, along with a carbon-based second active material with a specific aspect ratio, which enhances lithium intercalation sites and charge/discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is used as negative active material, then capacity is improved, but volume expansion and poor high-rate charge/discharge characteristics occur
Solution Approach 1:
The natural graphite particles are divided into primary particles (1-10 μm) and aggregated into secondary particles (5-20 μm), creating a segmented structure that improves electrolyte penetration and lithium ion diffusion pathways, thereby enhancing high-rate charge/discharge characteristics while maintaining capacity
Solution Approach 2:
The patent creates a composite structure by coating artificial graphite on the surface of natural graphite particles and forming aggregated secondary particles. This composite approach combines the high capacity of natural graphite with the improved kinetics of artificial graphite, resolving the contradiction between capacity and high-rate performance
2Quantity of substance
If natural graphite is used as negative active material, then capacity is improved, but volume expansion during charge/discharge occurs
Solution Approach 1:
By dividing natural graphite into smaller primary particles (1-10 μm) and controlling aggregation into secondary particles, the patent reduces overall volume expansion while maintaining capacity. The segmented structure allows for better stress distribution during lithium insertion/extraction cycles
Solution Approach 2:
The composite structure of natural graphite core with artificial graphite coating creates a more stable framework that accommodates volume changes during charge/discharge, reducing overall volume expansion while preserving the high capacity of natural graphite
3Reliability
If graphite particles are spheroidized and aggregated, then high-rate charge/discharge characteristics are improved, but particle density decreases
Solution Approach 1:
The controlled segmentation into primary and secondary particles with specific size ranges (primary: 1-10 μm, secondary: 5-20 μm) optimizes the balance between surface area for rapid lithium diffusion and particle density for compact electrode structure
Solution Approach 2:
The spheroidization of graphite particles improves high-rate charge/discharge characteristics by eliminating dead zones and improving electrolyte access, while the controlled aggregation into secondary particles maintains adequate density for practical electrode applications
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 results in improved cycle life, reduced volume expansion, and enhanced high-rate charge/discharge capabilities, with the negative active material exhibiting excellent chargeability and reduced resistance, effectively addressing the limitations of existing rechargeable lithium batteries.
Implementation Method 1
improved rapid charge and discharge characteristics by virtue of including secondary particles in which a plurality of primary particles are agglomerated and spheroidized, and tertiary particles in which the secondary particles are agglomerated, and an amorphous carbon coating layer surrounding the tertiary particles
Implementation Method 2
A negative active material according to some embodiments may exhibit excellent cycle life characteristics and reduced volume expansion characteristics
Data Source
AI summary
A negative active material for a rechargeable lithium battery and a rechargeable lithium battery that includes the negative active material. The negative active material includes a first active material, which includes tertiary particles of natural graphite in which secondary particles are agglomerated. Primary particles are agglomerated and spheroidized in the secondary particles. Artificial graphite is positioned on a surface of the primary particles and a surface of the secondary particles. An amorphous carbon coating layer surrounds the tertiary particles of natural graphite. Further, the negative active material includes a second active material, which includes a carbon-based material having an aspect ratio of about 2 to about 100.