Graphite-Silicon Anode Particle Sizing for Stable Cycle Life
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Solution Overview
Problem
Silicon-based materials in lithium secondary batteries experience significant volume changes during charging and discharging, leading to reduced ionic and electrical conductivity, and poor initial lifetime characteristics, making it difficult to commercialize their use as anode active materials.
Innovation Solution
An anode material layer comprising large-particle graphite, small-particle silicon-based material, and fine-particle graphite, with specific diameter ratios, is used to form a conductive path and improve adhesion, thereby enhancing electron conductivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based material is used as anode active material to increase capacity, then theoretical capacity increases significantly (4,200 mAh/g vs 372 mAh/g for graphite), but volume change during charging and discharging causes breaking of physical contact and spalling, resulting in decreased ionic conductivity, electrical conductivity, and initial lifetime characteristics
Solution Approach 1:
The silicon-based material is divided into fine particles with a specific size range (0.1 to 10 μm, preferably 0.5 to 5 μm). This segmentation reduces the overall volume change impact on the electrode structure, prevents particle aggregation, and maintains stable physical contact between active materials and conductive agents throughout charge-discharge cycles, thereby preserving electrical conductivity and initial lifetime characteristics while utilizing silicon's high capacity
Solution Approach 2:
The electrode is designed with a heterogeneous composition where fine silicon-based particles are distributed among graphite particles and conductive agents. This local quality approach ensures that silicon particles benefit from the buffering effect of surrounding graphite and conductive materials, maintaining optimal contact and conductivity in the local microenvironment while achieving high overall capacity
2Use of energy by moving object
If silicon-based material is used to achieve high capacity, then energy density increases, but volume change causes spalling and breaking of physical contact, leading to decreased electrical conductivity and ionic conductivity
Solution Approach 1:
Silicon-based material is segmented into fine particles (0.1 to 10 μm) that are dispersed throughout the electrode. This segmentation prevents large-volume expansion from causing structural collapse, maintains continuous conductive pathways, and preserves electrical conductivity while achieving high energy density through silicon's superior capacity
Solution Approach 2:
The electrode employs a composite structure combining silicon-based material with graphite and conductive agents in specific ratios. This composite approach leverages silicon's high capacity while graphite and conductive materials provide structural stability and maintain electrical pathways, achieving high energy density without sacrificing conductivity
Data Source
AI summary
The present disclosure relates to an anode for a lithium secondary battery, wherein an anode material layer is formed on at least one surface of an anode current collector, and the anode material layer includes large-particle graphite, a small-particle silicon-based material, and fine-particle graphite, and satisfies the following conditions 1 to 3: [Condition 1] Average diameter D50 of the large-particle graphite (D1): 1 to 50 µm [Condition 2] Average diameter D50 of the small-particle silicon-based material (D2):0.155D1 to 0.414D1 [Condition 3] Average diameter D50 of the fine-particle graphite (D3):0.155D1 to 0.414D1, or 0.155D2 to 0.414D2.