Si-Al-Fe Alloy Matrix for Lithium Battery Capacity Retention
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Solution Overview
Problem
Lithium secondary batteries using non-carbonaceous materials like Si and Sn face capacity deterioration due to volumetric expansion during charge and discharge, which affects the battery's lifespan.
Innovation Solution
A silicon-based alloy with a specific composition of Si, Al, and Fe, including silicon nanoparticles dispersed in an alloy matrix with a Si3Al3Fe2/Si2Fe ratio of 2 to 12, is used as a negative active material to inhibit volumetric expansion and improve capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If non-carbonaceous materials such as Si and Sn are used as negative active materials, then capacity density is improved (at least 10 times greater than graphite), but volumetric expansion occurs during charge and discharge, causing capacity deterioration
Solution Approach 1:
The patent uses a composite alloy matrix consisting of Si-Al-Fe intermetallic compounds (specifically SiAlON phase and SiO2 phase) combined with inactive silicon. This composite structure provides both high capacity density from the silicon content and structural stability to accommodate volumetric expansion during lithium insertion/extraction cycles, thereby maintaining capacity retention
Solution Approach 2:
The patent optimizes the compositional parameters of the alloy matrix, specifically controlling the Si/Al/Fe atomic ratio and the ratio of SiAlON to SiO2 phases. By adjusting these parameters, the material achieves a balance between active silicon content (for high capacity) and matrix stability (for preventing expansion damage), resolving the contradiction between capacity density and capacity retention
2Quantity of substance
If silicon content is increased to improve capacity density, then more lithium ions can be intercalated, but volumetric expansion increases, causing greater damage to the electrode structure
Solution Approach 1:
The inactive silicon and Si-Al-Fe intermetallic compound matrix act as an intermediary structure that surrounds and constrains the active silicon nanoparticles. This intermediary matrix accommodates the volumetric expansion of active silicon during lithium intercalation, preventing direct structural damage to the electrode while still allowing high lithium ion capacity through the active silicon content
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 silicon-based alloy with a balanced Si3Al3Fe2/Si2Fe ratio enhances the strength of the alloy matrix, reducing damage from volumetric expansion and improving the capacity retention rate of lithium batteries during repeated charge and discharge cycles.
Implementation Method 1
due to volumetric expansion of the materials during a charge and discharge process, the capacity of the battery may deteriorate
Data Source
AI summary
A negative active material, a lithium battery including the negative active material, and a method of preparing the negative active material. The negative active material includes a silicon-based alloy including Si, Al, and Fe. The silicon-based alloy includes an active phase of silicon nanoparticles and an inactive phase of Si3Al3Fe2 and Si2Fe in a ratios suitable to improve the lifespan of the lithium battery.