Graphite Composite Particles for Battery Electrode Density Control
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Solution Overview
Problem
The pressing of negative electrodes to increase packing density leads to heterogeneous density distribution, reduced permeability of electrolytic solution, and residual stress, which degrades the cycle characteristics of lithium ion secondary batteries.
Innovation Solution
A graphite-based active material comprising first and second composite particles, where the second composite particle has a higher mass fraction of non-graphite-based carbon material, is used to create a homogeneous density distribution and improve electrolyte retention, comprising a first graphite core particle with a low hardness and a second graphite core particle with a high hardness, ensuring uniform pressure transmission during pressing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the negative electrode is pressed to increase packing density, then the capacity is improved, but the density distribution becomes heterogeneous and cycle characteristics degrade
Solution Approach 1:
The patent applies local quality by creating particles with non-uniform carbon material distribution - the surface layer has a different carbon content (5-20 mass%) compared to the interior (0-5 mass%). This local differentiation allows the particle surface to interact properly with electrolyte while the interior maintains high density, resolving the contradiction between packing density and density distribution uniformity during electrode pressing.
2Quantity of substance
If the negative electrode is pressed to increase packing density, then the capacity is improved, but the electrolyte permeability is reduced
Solution Approach 1:
The surface layer of the graphite particles is designed with higher carbon material content (5-20 mass%) compared to the interior, creating a local quality difference. This surface enrichment maintains adequate void spaces and porosity at the particle surface, ensuring electrolyte permeability is preserved even when the overall electrode packing density is increased through pressing.
3Quantity of substance
If the negative electrode is pressed to increase packing density, then the capacity is improved, but residual stress increases
Solution Approach 1:
The patent changes the physical-chemical parameters of the graphite particles by controlling the carbon material distribution and heat treatment temperature (400-1000°C). This creates particles with specific mechanical properties that reduce residual stress generation during pressing, allowing high packing density to be achieved without excessive residual stress that would degrade cycle characteristics.
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
This approach enhances the cycle characteristics of lithium ion secondary batteries by maintaining a moderate void size near the surface, improving electrolyte permeability, and reducing residual stress, thereby increasing the battery's capacity retention and cycle life.
Implementation Method 1
a non-aqueous electrolytic solution prepared by dissolving a lithium salt in a non-aqueous solvent
Implementation Method 2
a negative electrode including a negative electrode active material of a carbon material capable of intercalating and deintercalating a lithium ion
Data Source
AI summary
A graphite-based active material including: a first composite particle including a first graphite core particle and a first non-graphite-based carbon material covering the surface of the first graphite core particle; and a second composite particle including a second graphite core particle and a second non-graphite-based carbon material covering the surface of the second graphite core particle, wherein the mass fraction of the second non-graphite-based carbon material in the second composite particle, mass fraction B, is 5% by mass or more and more than the mass fraction of the first non-graphite-based carbon material in the first composite particle, mass fraction A, and the proportion of the second composite particle to the total of the first composite particle and the second composite particle is 1% by mass or more.