Carbon-Coated Graphite Anode Material Balancing 2C Rate and Efficiency
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Solution Overview
Problem
Current carbon materials for lithium ion secondary battery negative electrodes, such as mesophase-based graphite particles, face issues with low initial efficiency and insufficient 2C discharge rate due to high specific surface area and inadequate firing conditions, which hinder their application in hybrid vehicles requiring high input-output characteristics.
Innovation Solution
Pulverizing mesophase microbeads to achieve a specific particle diameter and graphitizing them at moderate temperatures, followed by coating with amorphous carbon and firing at lower temperatures to form a carbonaceous film, resulting in a carbon material with improved initial efficiency and 2C discharge rate while maintaining a low specific surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mesophase-based graphite particles are used to improve cycle durability, then cycle durability is improved, but input-output characteristics deteriorate
Solution Approach 1:
The patent applies local quality by creating a dual-structure carbon material where mesophase-based graphite particles (providing cycle durability) are coated with amorphous carbon particles (providing input-output characteristics). Each component maintains its local functional properties while contributing to overall performance.
Solution Approach 2:
The patent uses composite materials by combining mesophase-based graphite particles with amorphous carbon particles to create a hybrid carbon material that exhibits both excellent cycle durability and superior input-output characteristics, overcoming the limitations of single-component materials.
2Power
If particle diameter is reduced to improve input-output characteristics, then input-output characteristics are improved, but specific surface area increases causing low initial efficiency
Solution Approach 1:
The patent applies parameter changes by carefully controlling the particle diameter of mesophase-based graphite particles within a specific range (0.5-5 μm) and adjusting the coating amount of amorphous carbon (0.1-10 mass%) to optimize both input-output characteristics and initial efficiency, demonstrating the importance of precise parameter control.
Solution Approach 2:
The amorphous carbon coating provides local quality improvement by creating a conductive network on the particle surfaces, enhancing electron transport and initial efficiency without requiring further reduction in particle diameter.
3Power
If specific surface area is increased to improve input-output characteristics, then input-output characteristics are improved, but initial efficiency decreases
Solution Approach 1:
The patent resolves this contradiction by creating a composite structure where amorphous carbon particles coat the mesophase-based graphite particles, providing high surface area for reactions while the core particles maintain structural integrity and efficiency.
Solution Approach 2:
The amorphous carbon coating acts as an intermediary layer that facilitates lithium ion transport and electron conduction, improving input-output characteristics without directly exposing excessive surface area that would cause side reactions and reduce initial efficiency.
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 resulting carbon material exhibits enhanced initial efficiency and 2C discharge rate with a reduced specific surface area, addressing the limitations of existing materials and enabling stable performance in lithium ion secondary batteries for hybrid vehicles.
Implementation Method 1
firing a graphitized material particle coated with the carbonaceous precursor at 900°C to 1200°C for more than 3 hours to thereby form the carbonaceous fired body
Implementation Method 2
graphitizing the carbonaceous particles at 2600°C to 3200°C to form graphitized material particles
Data Source
AI summary
Provided is a carbon material for a negative electrode of a lithium ion secondary battery, which has a small particle diameter, high initial charge-discharge efficiency, and a high 2C discharge rate, and achieves both input-output characteristics and durability. Disclosed is a carbon material for a negative electrode of a lithium ion secondary battery, in which a 50% by volume particle diameter (D50) in a cumulative frequency distribution is 1.0 µm or more and less than 5.0 µm, a specific surface area (SBET) by a BET method is 6.5 m2/g or less, a tap density (DTAP) is 0.70 g/cm3 or more, and a Raman R value obtained by Raman spectroscopy is more than 0.100 and less than 0.300, and the carbon material has a carbonaceous film on a surface of graphitized material particles of a mesophase microbead.