Negative Electrode Coating for Li-Ion Power and Efficiency
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Solution Overview
Problem
The existing use of graphite as a negative electrode in nonaqueous electrolyte secondary batteries limits input/output characteristics, and amorphous carbon coatings on graphite surfaces can lead to electrolyte decomposition and decreased charge/discharge efficiency, especially at the initial charge/discharge stage.
Innovation Solution
A secondary battery negative electrode with a film containing elements like P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, or Ta covering amorphous carbon on active material particles, which improves lithium ion permeability and reduces reaction resistance, formed by exposing the electrode precursor to an atmosphere containing the film's raw material at 200°C or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If amorphous carbon is provided on the surface of the negative electrode active material to improve input/output characteristics, then the input/output characteristics are improved, but the electrolyte liquid is decomposed and charge/discharge efficiency decreases
Solution Approach 1:
The patent applies different materials to different locations: amorphous carbon is applied to the surface of graphite particles to improve input/output characteristics, while a protective film containing specific elements (P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, or Ta) is formed on the surface of the amorphous carbon to prevent electrolyte decomposition. This local differentiation allows each layer to perform its specific function optimally.
Solution Approach 2:
The negative electrode active material uses a composite structure combining graphite particles with amorphous carbon coating, and further combines this with a protective film containing specific elements. This multi-layer composite structure integrates the high capacity of graphite with the improved kinetics of amorphous carbon and the protective properties of the element-containing film, resolving the contradiction between power and efficiency.
2Power
If amorphous carbon is used to cover graphite particles to improve input/output characteristics, then the input/output characteristics are improved, but electrolyte decomposition occurs especially at initial charge/discharge stage
Solution Approach 1:
The protective film containing specific elements (P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, or Ta) acts as an intermediary layer between the amorphous carbon and the electrolyte. This intermediate film prevents direct contact between the electrolyte and amorphous carbon surface, thereby preventing electrolyte decomposition while allowing lithium ion transport to maintain improved input/output characteristics.
Solution Approach 2:
The patent converts the potentially harmful effect of amorphous carbon (electrolyte decomposition) into a benefit by forming a protective film that prevents decomposition. The amorphous carbon's high reactivity, which initially causes electrolyte decomposition, is harnessed for improved lithium ion insertion/extraction kinetics, while the protective film eliminates the harmful decomposition effect.
3Device complexity
If graphite is used as negative electrode active material, then the battery structure is simple and cost-effective, but input/output characteristics are limited
Solution Approach 1:
The patent changes the surface properties of graphite particles by coating with amorphous carbon and forming a protective film containing specific elements. This parameter change (surface composition and structure) transforms the electrode from having limited input/output characteristics to having enhanced power capability, while maintaining the overall graphite-based structure for simplicity.
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 input/output characteristics and maintains charge/discharge efficiency while suppressing electrolyte decomposition and degradation during high-temperature storage.
Implementation Method 1
the film is formed by exposing the negative electrode precursor to an atmosphere at 200° C. or less containing a raw material of the film
Implementation Method 2
amorphous carbon which covers at least parts of surfaces of the active material particles
Implementation Method 3
the film having a lithium ion permeability
Data Source
AI summary
A secondary-battery negative electrode includes: a negative electrode collector; and a negative electrode active material layer provided on a surface of the negative electrode collector, and the negative electrode active material layer includes active material particles and amorphous carbon which covers at least parts of surfaces of the active material particles. At least a part of a surface of the amorphous carbon is covered with a film having a lithium ion permeability, the film contains an element M, and the element M is at least one selected from the group consisting of P, Si, B, V, Nb, W, Ti, Zr, Al, Ba, La, and Ta.