Coated Spherical Graphite Structure for Li-Ion Cycle Stability

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Solution Overview

Problem

Lithium ion secondary batteries require a negative electrode material with excellent cycle capacity-maintaining properties, especially for applications in vehicles where repeated charging and discharging lead to reduced battery life.

Innovation Solution

Spherically-shaped coated graphite with specific particle size and shape distributions, along with a carbonaceous substance coating, is used as the negative electrode material, optimizing the volume ratios of fine and coarse grains, secondary particle shapes, and pore volumes to enhance cycle capacity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If spherically-shaped graphite is used as negative electrode material, then charging-discharging efficiency is improved, but cycle capacity-maintaining property deteriorates due to expansion and shrinkage

Engineering Contradiction:

Improvecharging-discharging efficiencyVSAvoidcycle capacity-maintaining property

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The spherically-shaped graphite is segmented into primary particles with controlled size distribution (0.8-3.0 μm diameter range with specific volume ratios). This segmentation reduces internal stress during lithium insertion/extraction, mitigating expansion and shrinkage while maintaining high charging-discharging efficiency through optimized particle size distribution.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses composite material structure by combining spherically-shaped graphite with specifically controlled pore structures (pore volume ≤0.017 cm³/g, pore size 7.8-36.0 nm) and surface coatings. This composite approach maintains the high conductivity and efficiency of graphite while the controlled pores and surface structure suppress harmful expansion and shrinkage, improving cycle capacity-maintaining property.

Inventive Principle:

Principle #40Composite materials

2Productivity

If pore volume is increased to improve lithium ion diffusion, then charging efficiency is improved, but structural stability deteriorates leading to greater expansion and shrinkage

Engineering Contradiction:

Improvelithium ion diffusion efficiencyVSAvoidstructural stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The invention optimizes pore volume to a specific range (≤0.017 cm³/g) and pore size distribution (7.8-36.0 nm) to achieve the right balance. This parameter optimization allows sufficient lithium ion diffusion pathways while maintaining structural integrity, preventing excessive expansion and shrinkage during charge-discharge cycles.

Inventive Principle:

Principle #35Parameter changes

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 spherically-shaped coated graphite significantly reduces cycle capacity degradation, maintaining high performance and efficiency in lithium ion secondary batteries, particularly in vehicles, by suppressing expansion and shrinkage and improving charging-discharging efficiency.

Implementation Method 1

Lithium ions move between the negative electrode and the positive electrode in the discharging and charging processes

Methodology Applied

Scientific EffectIonic conduction: Conduction (electrical)

Implementation Method 2

a carbonaceous substance covering the spherically-shaped graphite, wherein a pore volume of pores with a pore size of not less than 7.8 nm and not more than 36.0 nm is not more than 0.017 cm3/g

Methodology Applied

Scientific EffectPhysical containment: Physical Containment

Data Source

PatentUS11840452B2Spherically-shaped coated graphite, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Publication Date: 2023.12.12 JFE CHEMICAL CORP

AI summary

Provided is spherically-shaped coated graphite exhibiting excellent cycle capacity-maintaining property when used as a negative electrode material for a lithium ion secondary battery. The spherically-shaped coated graphite includes: spherically-shaped graphite in which primary particles with an equivalent spherical diameter of not more than 0.8 μm have a volume ratio of more than 40.0% and not more than 70.0%, and primary particles with an equivalent spherical diameter of not less than 1.5 μm and not more than 3.0 μm have a volume ratio of not less than 3.0% and not more than 17.0%, in a particle size distribution of primary particles obtained using X-ray computed tomography; and a carbonaceous substance covering the spherically-shaped graphite, and a pore volume of pores with a pore size of 7.8 nm to 36.0 nm is not more than 0.017 cm3/g, and a mass of infiltrated dibutyl phthalate is less than 0.70 g/cm3.