Silicon-Anode Li-Ion Battery Electrolyte for Stable SEI Cycling
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Solution Overview
Problem
Lithium ion secondary batteries using silicon or silicon oxide as negative electrode active materials face significant challenges due to large volume expansion during charging, leading to damage of the solid electrolyte interface film and deterioration of cycle characteristics.
Innovation Solution
Incorporating an imide salt containing a first element such as K, Na, Mg, Ca, Cs, Al, or Zn in the electrolytic solution, along with a compound containing the same element in the negative electrode active material, to form a coating layer that stabilizes the SEI film and enhances cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If silicon or silicon oxide is used as negative electrode active material to increase capacity, then the battery capacity is improved, but the volume expansion during charging damages the SEI film and deteriorates cycle characteristics
Solution Approach 1:
The patent applies preliminary action by adding an imide salt containing a first element (K, Na, Mg, Ca, Cs, Al, or Zn) to the electrolytic solution before battery operation. This imide salt proactively forms a stable coating layer on the silicon-based negative electrode active material surface during initial cycles, preventing subsequent SEI film damage from volume expansion. The compound containing the first element in the negative electrode active material works synergistically with the imide salt to pre-establish protective structures that withstand charging-induced expansion.
Solution Approach 2:
The imide salt containing the first element acts as an intermediary substance between the silicon-based negative electrode active material and the electrolytic solution. It forms a mediating coating layer that buffers the harmful interaction between the expanding silicon and the electrolyte, preventing direct contact that would cause SEI film breakdown. This intermediary layer transmits mechanical stress from volume expansion without allowing electrolyte decomposition, thus protecting cycle characteristics while maintaining high capacity.
2Quantity of substance
If the negative electrode active material expands in volume during charging, then the capacity is improved, but the SEI film is damaged and electrolytic solution decomposes
Solution Approach 1:
The patent implements beforehand cushioning by incorporating a compound containing the first element (K, Na, Mg, Ca, Cs, Al, or Zn) within the negative electrode active material structure and adding an imide salt of the first element to the electrolytic solution. This combination creates a cushioning effect that absorbs and distributes the mechanical stress from volume expansion before it can damage the SEI film or cause electrolyte decomposition. The imide salt forms a resilient coating layer that cushions against expansion forces, preventing harmful effects while maintaining capacity.
3Ease of operation
If conventional electrolytic solutions are used with silicon-based negative electrodes, then the battery operates, but the cycle characteristics deteriorate due to SEI film damage
Solution Approach 1:
The patent applies parameter changes by modifying the electrolytic solution composition to include an imide salt containing the first element (K, Na, Mg, Ca, Cs, Al, or Zn) at a specific concentration (5-20 molar proportion relative to lithium salt). This parameter change in electrolyte composition fundamentally alters the interfacial chemistry between the electrolyte and silicon-based negative electrode, transforming the unstable SEI film formation process into a stable coating layer formation process. The changed electrolyte parameters enable both easy operation and improved cycle characteristics.
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 solution significantly improves the cycle characteristics of the battery by preventing decomposition of the electrolytic solution and maintaining the integrity of the SEI film, resulting in enhanced performance and longevity.
Implementation Method 1
a solid electrolyte interface (SEI) film formed on the surface of the negative electrode active material
Implementation Method 2
the electrolytic solution is decomposed and the cycle characteristics of the battery deteriorate
Data Source
AI summary
A lithium ion secondary battery includes: a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolytic solution. The negative electrode includes a negative electrode active material which contains silicon or a silicon alloy and a compound containing a first element, the electrolytic solution contains an imide salt which contains the first element and an imide anion, and the first element is any one or more elements selected from the group consisting of K, Na, Mg, Ca, Cs, Al, and Zn.