Negative Electrode Composite Particle Design for Lithium Ion Batteries
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Solution Overview
Problem
The challenge in lithium ion secondary batteries is that increasing the thickness and density of the negative electrode to enhance capacity leads to decreased electrolyte solution permeability and lithium ion acceptability, resulting in potential lithium deposition issues.
Innovation Solution
A negative electrode comprising a mixture of first and second composite particles, where the first particles have a larger average diameter and lower non-graphite-based carbon coating, and the second particles have a smaller diameter and higher carbon coating, with a specific mass ratio and density range, to achieve uniform density and improved lithium ion acceptability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the thickness and density of the negative electrode are increased to enhance capacity, then the battery capacity is improved, but the electrolyte solution permeability decreases and lithium ion acceptability deteriorates
Solution Approach 1:
The patent applies local quality by creating distinct regions within the negative electrode with different properties. The surface region contains particles with smaller average diameter and higher non-graphite carbon coating content, providing high electrolyte permeability and lithium ion acceptability. The interior region contains particles with larger average diameter and lower non-graphite carbon coating content, providing high capacity. This spatial differentiation of particle properties resolves the contradiction between capacity and ion acceptability.
Solution Approach 2:
The patent uses composite materials by combining two types of composite particles with different characteristics. Each composite particle consists of a core material and a non-graphite-based carbon coating layer. The mixture of particles with different size and coating content ratios creates a composite electrode structure that simultaneously achieves high capacity and high lithium ion acceptability through the synergistic effects of different particle types.
2Quantity of substance
If the density of the negative electrode is increased to improve capacity, then the energy density is improved, but the electrolyte solution permeability decreases causing lithium deposition
Solution Approach 1:
The patent prevents lithium deposition by creating a high-permeability surface layer through the use of particles with smaller average diameter and higher non-graphite carbon coating content. This surface region with enhanced electrolyte access prevents lithium ion accumulation and deposition, while the interior region with larger particles maintains high energy density. The local quality differentiation eliminates the harmful effect of lithium deposition while preserving high energy density.
3Reliability
If the non-graphite-based carbon coating content is increased to improve lithium ion acceptability, then the charge and discharge cycle characteristics are improved, but the electrode density decreases
Solution Approach 1:
The patent applies local quality by concentrating particles with high non-graphite carbon coating content (20-80 mass%) in the surface region, where they provide excellent lithium ion acceptability and charge-discharge cycle characteristics. The interior region uses particles with lower coating content (5-20 mass%) to maintain high density and energy storage capacity. This spatial distribution optimizes both cycle life and energy density.
Solution Approach 2:
The patent uses composite materials by combining particles with different non-graphite carbon coating content ratios. The high-coating particles (20-80 mass%) provide superior electrochemical performance and cycle stability, while the low-coating particles (5-20 mass%) provide high density. The composite mixture achieves both high reliability and high energy density through the synergistic combination of different material compositions.
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 configuration enhances lithium ion acceptability and cycle characteristics by ensuring uniform electrode density and improved electrolyte solution permeability, thereby increasing battery capacity and longevity.
Implementation Method 1
a carbonaceous layer present on its surface... a carbon material capable of occluding and releasing lithium ions
Data Source
Figure 1
AI summary
There is provided a negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer on the current collector, wherein the negative electrode active material layer comprises: a first composite particle comprising a first graphite core particle and a first non-graphite-based carbon material coating a surface thereof; and a second composite particle comprising a second graphite core particle and a second non-graphite-based carbon material coating a surface thereof, and wherein an average particle diameter dA (D50) of the first composite particles is 5 to 30 µm; an average particle diameter dB (D50) of the second composite particles is 2 to 25 µm, and is smaller than the average particle diameter dA of the first composite particles; the mixing ratio of the first composite particle A and the second composite particle B is 50 : 50 to 95 : 5 in mass ratio (A : B); and a density of the negative electrode active material layer is 1.4 to 1.7 g/cm3.