Silicon Anode Particle Structure for Stable Li-Ion Battery Cycling
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Solution Overview
Problem
Lithium ion secondary batteries face poor cycle characteristics due to significant volume expansion of silicon-based negative electrode materials, leading to damage and degradation of the conductive path, interface peeling, and SEI coating film cracks, which reduces battery performance.
Innovation Solution
A negative electrode material comprising silicon particles with an internal region of large crystallite size and a surface region of amorphous silicon or small crystallite size, along with a controlled thickness and composition of the surface region, to uniformly diffuse lithium ions and suppress local volume changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon is used as negative electrode active material to achieve higher capacity, then battery capacity is improved, but volume expansion during charging causes damage to conductive path and interface peeling
Solution Approach 1:
The invention applies local quality by creating a surface region with different properties (amorphous or fine crystalline silicon with crystallite size of 200 nm or less) compared to the internal region (coarse crystalline silicon with crystallite size of more than 200 nm). This gradient structure allows the surface to accommodate volume expansion while the interior maintains structural integrity, resolving the contradiction between high capacity and cycle stability.
Solution Approach 2:
The invention uses composite materials by combining silicon particles with a specific dual-region structure (amorphous/fine crystalline surface region + coarse crystalline internal region). This composite structure leverages the advantages of both amorphous silicon (flexibility to accommodate expansion) and crystalline silicon (high capacity), achieving both improved capacity and cycle characteristics.
2Quantity of substance
If silicon particles undergo volume expansion during charging, then lithium ion insertion is enhanced, but conductive path is cut and SEI coating film cracks occur
Solution Approach 1:
The surface region with amorphous or fine crystalline structure (crystallite size of 200 nm or less) provides local flexibility to accommodate volume expansion during lithium ion insertion, while the coarse crystalline internal region (crystallite size of more than 200 nm) maintains overall structural integrity. This local quality gradient prevents conductive path disruption and SEI film cracking.
3Quantity of substance
If the negative electrode active material layer is made thicker to increase capacity, then battery capacity is improved, but interface peeling between active material layer and current collector occurs
Solution Approach 1:
The surface region of the silicon particles, comprising amorphous or fine crystalline silicon (crystallite size of 200 nm or less), acts as a buffer zone that accommodates volume expansion during charging. This local quality gradient at the particle surface prevents stress concentration at the interface between the active material layer and current collector, maintaining adhesion even with thicker active material layers.
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 proposed electrode material enhances the cycle characteristics of lithium ion secondary batteries by ensuring uniform lithium diffusion and reducing local stress, thereby improving discharge capacity and maintaining battery performance over cycles.
Implementation Method 1
The surface region includes amorphous silicon or silicon having a crystallite size of 200 nm or less. The internal region includes silicon having a crystallite size of more than 200 nm
Data Source
AI summary
This negative electrode material for a lithium ion secondary battery may include silicon particles. The silicon particles may have an average particle size of 1 μm or more and 10 μm or less. Each of the silicon particles may have an internal region and a surface region. The surface region may include amorphous silicon or silicon having a crystallite size of 200 nm or less. The internal region may include silicon having a crystallite size of more than 200 nm.