Composite Graphite Anode Structure for Low-Expansion Fast Charging
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Solution Overview
Problem
Rechargeable lithium batteries face challenges in achieving high power characteristics, such as cycle life and reduced volume expansion, due to limitations in intercalation sites and charge/discharge efficiency.
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, along with a carbon-based second active material with a specific aspect ratio, which increases intercalation sites and improves charge/discharge efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If natural graphite is used as the negative active material, then capacity is improved, but volume expansion and poor high-rate charge/discharge performance occur
Solution Approach 1:
The patent uses a composite structure combining natural graphite particles with artificial graphite coating layers. The natural graphite provides high capacity through its layered structure, while the artificial graphite coating suppresses volume expansion and improves structural stability during charge/discharge cycles, thereby enhancing cycle life and high-rate performance
Solution Approach 2:
The patent modifies the surface properties of natural graphite by coating it with artificial graphite and controlling particle size distribution. These parameter changes reduce the harmful volume expansion effects while maintaining the high capacity benefits of natural graphite, resolving the contradiction between capacity and reliability
2Quantity of substance
If graphite particle size is increased to improve capacity, then more intercalation sites are available, but charge/discharge efficiency decreases
Solution Approach 1:
The patent segments the graphite structure into a hierarchical particle size distribution with small primary particles (3-10 μm) that provide short diffusion paths for high charge/discharge efficiency, and larger tertiary particles formed by agglomeration that provide increased intercalation sites. This segmentation resolves the contradiction between having enough intercalation sites and maintaining efficient charge/discharge rates
3Reliability
If artificial graphite coating is applied to suppress volume expansion, then structural stability is improved, but manufacturing complexity increases
Solution Approach 1:
The artificial graphite coating is applied in advance during the particle formation process itself, rather than as a separate post-treatment step. This preliminary action integrates the coating step into the existing manufacturing workflow, providing structural stability benefits while minimizing additional manufacturing complexity
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 negative active material exhibits improved cycle life, reduced volume expansion, and enhanced high-rate charge/discharge capabilities, leading to better performance in lithium batteries.
Implementation Method 1
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.
Implementation Method 2
A negative active material and a rechargeable lithium battery including the negative active material... The negative active material exhibits improved cycle life, reduced volume expansion, and enhanced high-rate charge/discharge capabilities
Data Source
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AI summary
A negative active material for a rechargeable lithium battery and a rechargeable lithium battery that includes the negative active material are disclosed. 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.