Si-Sn-V Alloy Negative Electrode for Battery Cycle Life
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Solution Overview
Problem
Lithium ion secondary batteries using silicon-based negative electrode materials face a trade-off between capacity and cycle durability due to amorphous-crystal phase transitions, leading to reduced cycle life and capacity retention.
Innovation Solution
A negative electrode active material comprising a Si-Sn-V alloy with specific mass percentage ranges (Si: 27-100%, Sn: 0-73%, V: 0-73%) is used, with Sn and V additives to suppress phase transitions, ensuring high capacity and extended cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Si fine particles are used as negative electrode active material to achieve high discharge capacity per volume, then the capacity is improved, but the negative electrode material undergoes amorphous-crystal phase transition when Si is alloyed with Li, causing volume change and reduction in cycle life
Solution Approach 1:
The invention changes the compositional parameters by introducing Sn and V elements to form a three-component alloy system (Si-Sn-V). This compositional modification suppresses the amorphous-crystal phase transition that occurs in pure Si when alloyed with Li, thereby maintaining structural stability and extending cycle life while preserving high discharge capacity.
Solution Approach 2:
The invention creates a composite alloy material combining Si, Sn, and V elements. The composite structure leverages the high capacity of Si while incorporating Sn and V to suppress harmful phase transitions. This composite approach allows simultaneous achievement of high capacity and improved cycle durability.
2Quantity of substance
If Si series active material is used to ensure high capacity, then the capacity is improved, but the cycle durability is reduced due to volume change from phase transition
Solution Approach 1:
By modifying the alloy composition parameters and introducing Sn and V elements, the invention suppresses the phase transition behavior. This parameter change strategy maintains the high capacity characteristics of Si while improving cycle durability through compositional optimization.
Solution Approach 2:
Sn and V elements act as intermediary components that mediate the interaction between Si and Li. These intermediary elements suppress the direct amorphous-crystal phase transition in Si during lithium alloying, thereby protecting the structural integrity and extending cycle durability while maintaining high capacity.
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 Si-Sn-V alloy maintains high discharge capacity and cycle durability, with discharge capacity retention of 92% after 50 cycles and 44% after 100 cycles, outperforming conventional materials.
Implementation Method 1
the negative electrode material shifts from an amorphous state to a crystalline state when Si is alloyed with Li. As a result, the volume is greatly changed, which causes a reduction in cycle life of the electrode
Data Source
AI summary
A negative electrode active material for an electric device includes an alloy containing Si in a range of greater than or equal to 27% by mass and less than 100% by mass, Sn in a range of greater than 0% by mass and less than or equal to 73% by mass, V in a range of greater than 0% by mass and less than or equal to 73% by mass, and inevitable impurities as a residue. The negative electrode active material can be obtained with, for example, a multi DC magnetron sputtering apparatus by use of Si, Sn, and V as targets. An electric device using the negative electrode active material can achieve long cycle life and ensure a high capacity and cycle durability.