Fast-Charging Li-Ion Electrolytes That Shift SEI Formation to the Cathode
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Solution Overview
Problem
Developing stable electrodes for fast-charging lithium ion batteries is challenging due to the severe volumetric changes in Si anodes, which lead to premature cycle life failure and safety issues caused by solid-electrolyte interphase (SEI) formation on the anode.
Innovation Solution
The solution involves using an electrolyte solution that forms a solid-electrolyte interphase (SEI) on the cathode rather than the anode, with specific electrolyte compositions and additives that promote SEI formation on the cathode while minimizing or preventing it on the anode, and potentially coating the cathodes to enhance stability and safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SEI-forming additive is added to electrolyte to form stable SEI on Si anode, then anode stability is improved, but SEI formation consumes lithium ions and reduces battery capacity
Solution Approach 1:
The patent extracts the SEI formation process from the anode and relocates it to the cathode. By using a redox couple in the electrolyte that is inert toward the Si anode but forms SEI on the cathode, the harmful lithium ion consumption at the anode is eliminated while still providing the stabilizing SEI layer where it is needed.
Solution Approach 2:
The redox couple acts as an intermediary substance in the electrolyte. It mediates the SEI formation process by being reduced at the cathode to form the protective SEI layer, while remaining inert at the anode. This intermediary enables selective SEI formation without direct electrolyte-anode reactions that would consume lithium ions.
2Reliability
If conventional electrolyte is used with Si anode, then electrolyte is readily reduced on anode forming SEI, but this leads to continuous SEI formation and breakdown during cycling reducing cycle life
Solution Approach 1:
The patent inverts the conventional approach by reversing where SEI formation occurs. Instead of forming SEI on the anode (conventional approach), the electrolyte is engineered to form SEI on the cathode through the redox couple mechanism. This inversion prevents the continuous SEI formation and breakdown cycle that plagues Si anodes while maintaining the necessary protective SEI layer.
3Quantity of substance
If Si anode is used for high capacity, then battery capacity is improved, but severe volumetric changes during cycling cause electrode degradation and safety issues
Solution Approach 1:
The patent converts the harmful effect of volumetric changes in Si anodes into a benefit by eliminating SEI formation on the anode. The large volume expansion of Si during lithiation is no longer accompanied by harmful SEI formation and breakdown cycles. The redox couple ensures SEI forms only on the cathode, transforming the previously harmful anode-electrolyte interaction into a benign process that preserves both capacity and stability.
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
This approach improves the cycle life and safety of fast-charging lithium ion batteries by reducing anode degradation and maintaining high performance over multiple charge cycles, while also enhancing the battery's operational safety.
Implementation Method 1
the electrolyte solution is selected to create, at least during a formation stage of the cell, a solid-electrolyte interphase (SEI) upon the at least one cathode rather than on the at least one anode
Implementation Method 2
a redox couple in the electrolyte solution, having a first redox pair in the anode-contacting compartment and a second redox pair in the cathode-contacting compartment, wherein the first redox pair is inert with respect to the at least one anode and the second redox pair forms a solid electrolyte interphase (SEI) on the at least one cathode
Data Source
AI summary
Fast-charging lithium ion cells are provided, which have electrolytes that do not react with the cell anodes, but instead form a solid-electrolyte interphase (SEI) on the cathodes. Advantageously, such electrolytes improve the performance of the fast-charging cells, and enhance their lifetime and safety. Various electrolyte solutions and lithium ions are proposed to limit electrolyte interactions to the cathodes, or possibly even minimize or prevent these reactions by coating the cathodes. Redox couples may be used to prevent SEI formation on the anode, while promoting SEI formation on the cathode.