Sulfur-Modified Silicon-Carbon Anode Powder for SEI and Swelling Control
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Solution Overview
Problem
Existing silicon-based electrochemically active materials in Li-ion batteries suffer from large volume expansion during charging, leading to mechanical degradation and poor cycle performance due to SEI formation, which limits both capacity and cycle life, especially in batteries for electric vehicles.
Innovation Solution
A composite powder comprising silicon-based sub-particles embedded in a carbonaceous matrix with controlled sulfur content enhances the elasticity of the matrix, allowing it to accommodate volume changes and reduce SEI formation, thereby improving coulombic efficiency and cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon-based electrochemically active material is used in the anode to improve energy density, then the battery capacity increases, but the volume expansion during charging causes mechanical degradation and reduces cycle life
Solution Approach 1:
The patent embeds silicon-based particles inside carbonaceous particles, creating a nested structure where the inner silicon particles can expand and contract during lithiation/delithiation cycles while being contained within the outer carbon shell. This nesting approach allows the silicon to undergo volume changes without causing mechanical degradation to the overall particle structure, thereby maintaining cycle life while preserving high capacity.
Solution Approach 2:
The patent creates a composite particle consisting of silicon-based material embedded within a carbonaceous matrix. The carbonaceous component provides mechanical stability and structural integrity, while the silicon-based component provides high electrochemical capacity. This composite structure combines the advantages of both materials, enabling high capacity retention over many cycles.
2Quantity of substance
If silicon-based material is used to increase energy density, then more lithium ions can be stored, but SEI formation increases leading to lithium loss and poor cycle performance
Solution Approach 1:
The carbonaceous particle acts as an intermediary between the silicon-based material and the electrolyte. The carbon shell provides a stable interface that limits direct contact between the silicon and electrolyte, thereby reducing SEI formation. This intermediary layer protects the silicon from excessive SEI growth while still allowing lithium ion transport, preserving lithium availability for electrochemical reactions.
3Reliability
If thick SEI is formed on the anode to protect silicon particles, then particle stability improves, but electrical resistance increases limiting high current performance
Solution Approach 1:
The carbonaceous shell is designed to be thin yet flexible, providing just enough protection to stabilize the silicon particles during volume changes without creating a thick barrier that would impede electron and ion transport. The flexible nature of the carbon shell allows it to accommodate silicon expansion and contraction, maintaining particle integrity while preserving electrical conductivity for high-rate performance.
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 composite powder achieves higher initial and average coulombic efficiency and extended cycle life by minimizing mechanical stress and SEI formation, ensuring stable battery performance.
Implementation Method 1
the matrix material comprises a carbonaceous material, the powder further comprising sulfur, the sulfur content by weight in said powder being at least 0.1% of the content of carbonaceous material by weight and at most 1% of the content of carbonaceous material by weight
Implementation Method 2
its large volume expansion during charging, which is as high as 300% when the lithium ions are fully incorporated, e.g. by alloying or insertion, in the anode's active material—a process often called lithiation
Implementation Method 3
a thick SEI, a Solid-Electrolyte Interface, may be formed on the anode. A SEI is a complex reaction product of the electrolyte and lithium
Data Source
AI summary
A powder suitable for use in a negative electrode of a battery, wherein the powder comprises particles, wherein the particles comprise a matrix material and silicon-based sub-particles embedded in the matrix material, wherein the matrix material comprises a carbonaceous material, wherein the powder further comprises sulfur, the sulfur content by weight in said powder being at least 0.1% of the content of carbonaceous material by weight in said powder and at most 1% of the content of carbonaceous material by weight in said powder.