Silicon-Carbon Complex Particles for Battery Anodes
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Solution Overview
Problem
Lithium ion secondary batteries using layered polysilane as negative electrode active material face issues with high BET specific surface area, leading to accelerated electrolyte decomposition and low cycle characteristics due to the generation of Solid Electrolyte Interphase (SEI).
Innovation Solution
The development of complex particles comprising nano silicon aggregated particles with a carbon layer formed from amorphous carbon, where the nano silicon particles are produced by heating a layered polysilane and grinding to a specific diameter, followed by carbonization, to reduce the specific surface area and enhance dispersibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If layered polysilane is used as negative electrode active material, then capacity is improved, but BET specific surface area increases leading to electrolyte decomposition and low cycle characteristics
Solution Approach 1:
The patent applies local quality by forming a carbon layer specifically on the surface of silicon particles. This carbon coating provides different properties at the surface (protection, low reactivity) versus the interior (high lithium insertion capacity). The carbon layer acts as a protective barrier that prevents electrolyte decomposition at the particle surface while maintaining the high capacity of bulk silicon.
Solution Approach 2:
The patent creates a composite material structure combining silicon and carbon. The silicon core provides high lithium insertion capacity, while the carbon shell provides structural stability and protects against electrolyte decomposition. This composite approach allows the system to simultaneously achieve high capacity and good cycle characteristics by combining materials with complementary properties.
2Volume of moving object
If layered polysilane is heated to produce nano silicon particles, then particle size is reduced improving capacity, but particle aggregation increases reducing dispersibility
Solution Approach 1:
The patent uses a carbon shell (thin film) to encapsulate nano silicon particles. This carbon film provides a protective layer that prevents particle aggregation while maintaining small particle size. The flexible carbon shell allows the nano particles to remain dispersed and prevents them from clumping together, thus maintaining both small size and good dispersibility.
Solution Approach 2:
The patent controls the heating temperature and atmosphere parameters during synthesis to produce nano silicon particles with optimal size and surface properties. By carefully adjusting these parameters, the patent achieves small particle size while controlling surface characteristics to prevent aggregation and maintain dispersibility in the electrode matrix.
3Reliability
If carbon layer is formed on silicon particles, then electrolyte decomposition is suppressed, but manufacturing complexity increases
Solution Approach 1:
The patent forms the carbon layer during the initial heating treatment of layered polysilane, before electrode assembly. This preliminary action integrates the carbon coating step into the material synthesis process itself, rather than adding it as a separate post-processing step. The carbonization occurs during the heating treatment at 600-900°C, combining structure formation and surface protection in one operation.
Solution Approach 2:
The patent uses carbon as an intermediary material that mediates between silicon and the electrolyte. The carbon layer serves as an intermediate protective barrier that allows lithium ions to pass through while preventing direct contact between silicon and electrolyte. This intermediary approach simplifies the overall system by using a single material (carbon) to perform multiple functions: structural support, ion transport, and chemical protection.
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 reduces irreversible capacity, suppresses electrolyte decomposition, and improves cycle characteristics by stabilizing the negative electrode, resulting in enhanced initial capacity and prolonged battery life.
Implementation Method 1
nano silicon particles produced by heating a layered polysilane
Implementation Method 2
composited carbon layer formed from an amorphous carbon and at least covering one portion of the aggregated particles
Data Source
AI summary
Provided is a negative electrode active material including complex particles formed of: nano silicon aggregated particles produced by heating a layered polysilane represented by a composition formula of (SiH)n and having a structure in which multiple six-membered rings formed from silicon atoms are connected; and a composited carbon layer formed from an amorphous carbon and at least covering one portion of the aggregated particles. A mean particle diameter D50 of the aggregated particles is within a range of 0.2 μm to 30 μm, and a mean particle diameter D50 of the complex particles is within a range of 0.5 μm to 40 μm.