Silicon Anode Covering Structure for Battery Cycle Stability
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Solution Overview
Problem
Silicon-containing compounds in secondary batteries undergo significant volume changes during charging and discharging, leading to deterioration of the internal structure and reduced cyclability.
Innovation Solution
A secondary battery design featuring a Si-based negative electrode active material with a covering material that has an elastic modulus lower than the binder, allowing for expansion and contraction to prevent structure collapse, and includes a surface conductor to maintain electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a Si-containing compound is used as a negative electrode active material to increase battery capacity, then the battery capacity is improved, but the internal structure deteriorates due to volume changes during charging and discharging
Solution Approach 1:
The patent applies nesting by placing the Si-containing compound (active material core) inside a covering material layer. This nested structure allows the core to expand and contract during charging and discharging while being protected by the outer covering layer, thereby maintaining internal structure stability while utilizing the high capacity of silicon-based materials.
Solution Approach 2:
The covering material is designed with specific mechanical properties (elastic modulus of 0.1-10 GPa and elongation at break of 100% or more) to act as a flexible shell that can accommodate volume changes of the Si-containing compound during electrochemical cycles, preventing structural deterioration while maintaining battery capacity.
2Duration of action of stationary object
If the covering material has low elastic modulus to allow expansion and contraction, then cyclability is improved, but structural strength may be compromised
Solution Approach 1:
The patent optimizes the elastic modulus parameter of the covering material to a specific range (0.1-10 GPa) that balances flexibility for volume change accommodation with sufficient structural strength. This parameter optimization allows the material to exhibit both cyclability improvement through expansion/contraction and maintained structural integrity.
Solution Approach 2:
The patent employs composite material design by combining the Si-containing compound core with a polymer-based covering material having specific mechanical properties. This composite structure integrates the high capacity of silicon with the flexibility and strength of the polymer matrix, achieving both improved cyclability and maintained structural strength.
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 solution enhances the cyclability and energy density of the battery by minimizing structural deterioration and maintaining electrical conductivity during repeated charge cycles.
Implementation Method 1
The covering material has an elongation at break of 100% or higher, and has a recovery of 70% or higher after being stretched to an elongation at break of 100%. Thus, the secondary battery according to an embodiment allows the covering material to expand and contract in accordance with expansion and contraction of the active material core
Data Source
AI summary
A secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode includes a Si-based negative electrode active material and a negative electrode binder. The Si-based negative electrode active material includes an active material core and a covering material. The active material core includes a Si-containing compound. The covering material covers at least a portion of a surface of the active material core. The covering material has an elastic modulus lower than an elastic modulus of the negative electrode binder. The covering material has an elongation at break of 100% or higher, and has a recovery of 70% or higher after being stretched to an elongation at break of 100%.