Yolk-Shell Silicon-Carbon Particles for Stable Li-Ion Anodes
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Solution Overview
Problem
Existing lithium secondary batteries using silicon as a negative electrode material face issues with low first cycle Coulombic efficiency and poor long-term stability due to volume expansion and electrolyte penetration through carbon shell mesopores, leading to decreased capacity retention and rate-limiting properties.
Innovation Solution
A yolk-shell structured particle with a carbon shell and a silicon core is developed, where the carbon shell's pore size is reduced, and silica is partially etched to create a buffer structure, reducing electrolyte penetration and enhancing initial efficiency and cycle stability, and the silicon particle size is controlled through high-temperature heat treatment to improve rate-limiting properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a carbon shell with mesopores is used in silicon-carbon composite, then electrolyte penetration is enhanced, but side reactions increase causing decreased initial efficiency and Coulombic efficiency
Solution Approach 1:
The patent uses a carbon shell with controlled mesopores (2-3 nm) that balances electrolyte penetration and side reaction prevention. The porous structure allows necessary ion transport while the controlled pore size limits excessive electrolyte access to silicon surface, resolving the contradiction between electrolyte access and side reaction prevention.
Solution Approach 2:
The patent creates a silicon-carbon composite structure where carbon shell encapsulates silicon core. This composite approach combines the high capacity of silicon with the stability and conductivity of carbon, while the carbon shell acts as a barrier reducing direct electrolyte-silicon contact and minimizing side reactions.
2Quantity of substance
If silicon is used as negative electrode material, then theoretical capacity is significantly higher than graphite, but volume expansion by 300% causes continuous SEI layer production and poor long-term stability
Solution Approach 1:
The patent segments the silicon into small particles (50-200 nm) and encapsulates them within a carbon shell. This segmentation prevents continuous SEI formation by isolating individual silicon particles, while the carbon shell provides structural stability during volume expansion, maintaining long-term battery performance.
Solution Approach 2:
The carbon shell acts as a pre-established buffer that accommodates the 300% volume expansion of silicon during lithiation. This beforehand cushioning prevents structural collapse and continuous SEI formation, ensuring long-term stability while preserving the high capacity of silicon.
3Productivity
If silicon particle size is reduced to increase surface area, then capacity density improves, but first cycle Coulombic efficiency decreases
Solution Approach 1:
The patent applies different properties to different parts of the structure: the silicon core is divided into fine particles (50-200 nm) for high capacity density, while the carbon shell provides a protective environment that manages electrolyte interaction. This local differentiation allows high surface area without the penalty of low first cycle efficiency.
Solution Approach 2:
The carbon shell acts as an intermediary between the silicon particles and the electrolyte. It allows necessary lithium ion transport to reach the silicon surface for high capacity utilization, while simultaneously preventing excessive electrolyte contact that would cause low first cycle efficiency, thus mediating between these conflicting requirements.
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
The yolk-shell structure effectively buffers volume expansion, reduces electrolyte penetration, and enhances the initial efficiency and cycle stability of lithium secondary batteries, leading to improved rate-limiting properties and increased first cycle Coulombic efficiency.
Implementation Method 1
a carbon shell; and a silicon (Si) core provided inside the carbon shell, wherein at least a part of the shell is spaced apart from the core
Implementation Method 2
the particle with a yolk-shell structure has a micropore particle volume of 0.15 cm3/g or less
Data Source
AI summary
A particle with a yolk-shell structure including a shell including carbon; and a care including silicon (Si) provided inside the shell, wherein at least a part of the shell is spaced apart from the core, and the particle with the yolk-shell structure has a micropore volume of 0.15 cm3/g or less, and a method for preparing the same.