Negative Electrode Carbon Material for Li-Ion Batteries
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Solution Overview
Problem
Graphite carbon materials used in lithium ion secondary batteries exhibit high energy density but limited high-speed charge-discharge characteristics due to their high crystallinity, which restricts lithium ion diffusion, making them unsuitable for applications in hybrid vehicles.
Innovation Solution
A carbon material with a highly developed crystal structure is produced using a stock oil composition with specific properties, including a high 10 vol% distillation temperature, high aromatic component content, and sufficient normal paraffin content, to form extensive lithium ion diffusion channels and enhance charge-discharge capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If graphite carbon material with high crystallinity is used as negative electrode material, then energy density per unit volume is improved, but high-speed charge-discharge characteristics deteriorate due to limited lithium ion diffusion
Solution Approach 1:
The invention changes the structural parameters of graphite carbon material by controlling crystal orientation and interlayer spacing. Specifically, it develops (002) plane orientation perpendicular to the sheet surface and controls interlayer spacing to 0.335-0.345 nm, which maintains high energy density while improving lithium ion diffusion characteristics for high-speed charge-discharge performance
Solution Approach 2:
The invention creates a composite structure combining highly oriented graphite crystallites with controlled amorphous carbon phases. This composite approach at the microstructural level allows simultaneous achievement of high energy density from the crystalline graphite and improved ion diffusion from the controlled interlayer spacing and orientation
2Quantity of substance
If graphite carbon material is used to increase service capacity in compact batteries, then energy density is improved, but lithium ion diffusion in carbon layer is restricted
Solution Approach 1:
The invention optimizes physical parameters of the graphite structure including interlayer spacing (0.335-0.345 nm) and crystal orientation ((002) plane perpendicular to sheet surface). These parameter changes enable increased service capacity while maintaining adequate lithium ion diffusion rate by creating optimal pathways for ion transport
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 achieves excellent high-speed charge-discharge characteristics and increased charge capacity, making it suitable for lithium ion secondary batteries, particularly for use in hybrid vehicles.
Implementation Method 1
heavy oil is subjected to high-temperature treatment to cause thermal decomposition and polycondensation reaction
Implementation Method 2
thermal decomposition and polycondensation reaction, producing liquid crystal spheres referred to as the 'mesophase'
Implementation Method 3
when the bulk mesophase undergoes polycondensation to carbonization and solidification
Implementation Method 4
during charge-discharge, intercalation-deintercalation of lithium ions takes place at the edges of the hexagonal mesh
Data Source
AI summary
The invention provides a stock oil composition for a carbon material for a negative electrode for a lithium ion secondary battery, having a 10 vol% distillation temperature of 280°C or higher as the distillation property, a density of at least 0.90 g/cm3 at a temperature of 15°C and a normal paraffin content of at least 3 parts by weight with respect to 100 parts by weight as the total weight of the stock oil composition; and having an aromatic component content of 30-85 parts by weight with respect to 100 parts by weight as the total weight of the stock oil composition and an aromatic component molecular weight of 250-1600 when the aromatic components and non-aromatic components are separated by elution chromatography.