Silicon Anode Composite with Ionic Liquid for Stable Solid-State Cycling
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Solution Overview
Problem
Conventional solid-state batteries using high-capacity negative electrode active materials with large volume changes and sulfide-based solid electrolytes face issues with ion conduction path disappearance due to charge-discharge cycles, leading to capacity degradation, and existing solutions like binders and ionic liquids either increase resistance or react negatively with sulfide-based electrolytes.
Innovation Solution
A negative electrode composite material comprising a silicon-based active material, a sulfide-based solid electrolyte, and a specific ionic liquid with an anion donor number of 9 or less, such as BMPTFSI, is used to maintain ion conduction paths, suppressing capacity loss during charge-discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a high-capacity negative electrode active material with large volume change ratio is used, then battery capacity is improved, but ion conduction path disappears due to repeated volume changes, leading to capacity degradation
Solution Approach 1:
The invention changes the physical state of the electrolyte from solid to liquid (or gel-like) to enable the electrolyte to dynamically adapt to volume changes. The liquid/gel electrolyte can flow and deform to maintain contact with the active material surface during expansion and contraction, preserving ion conduction paths throughout charge-discharge cycles.
Solution Approach 2:
The liquid or gel electrolyte acts as an intermediary between the solid electrodes and provides a flexible ion conduction medium. This intermediary can accommodate volume changes better than solid electrolytes, maintaining continuous ion transport pathways even when electrode dimensions change during cycling.
2Strength
If a binder is blended to improve bonding properties at the solid-solid interface, then electrode robustness is improved, but battery resistance increases due to lack of electron and ion conductivity
Solution Approach 1:
The liquid or gel electrolyte serves as a mediator that provides both mechanical bonding and ionic conductivity simultaneously. Unlike conventional binders that only provide mechanical strength, the liquid/gel electrolyte maintains electrode integrity while ensuring continuous ion transport, eliminating the need for additional binder materials that would increase resistance.
Solution Approach 2:
The liquid or gel electrolyte performs multiple functions: it acts as the ion conduction medium, provides mechanical bonding between electrode components, and accommodates volume changes. This multi-functionality replaces the separate roles of conventional binders and electrolytes, avoiding the resistance penalty associated with non-conductive binders.
3Reliability
If an ionic liquid is blended to maintain the ion conduction path, then ion conduction is improved, but battery characteristics deteriorate due to reaction with sulfide-based solid electrolyte
Solution Approach 1:
The invention uses a liquid or gel electrolyte that can be easily replaced or regenerated if degradation occurs. This approach accepts that the electrolyte may undergo some chemical changes during cycling but maintains performance through replacement, avoiding the need to prevent all chemical reactions through complex material selection.
Solution Approach 2:
The invention changes from using ionic liquids with high reactivity toward using liquid or gel electrolytes with controlled composition and properties. By adjusting the physical state and chemical composition parameters, the electrolyte maintains ion conduction while reducing harmful reactions with sulfide-based solid electrolytes.
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 composite material effectively maintains ion conduction paths, enhancing cycle life and capacity retention in solid-state batteries by using a low-reactivity ionic liquid that supports volume changes in silicon-based electrodes.
Implementation Method 1
a high-capacity negative electrode active material such as a silicon-based negative electrode active material has a large volume change ratio due to charge and discharge. Therefore, in the negative electrode material including a high-capacity negative electrode active material, a large volume change repeatedly occurs due to repeated charge and discharge.
Implementation Method 2
in the case of a battery where the solid electrolyte is sulfide-based, since the ionic liquid and the sulfide-based solid electrolyte are reactive to each other, the battery characteristics deteriorate due to the reaction
Data Source
AI summary
To blend a specific ionic liquid in the negative electrode composite material. Specifically, the negative electrode composite material includes a negative electrode active material, a solid electrolyte, and an ionic liquid, wherein the negative electrode active material is a silicon-based negative electrode active material, the solid electrolyte is a sulfide-based solid electrolyte, and the ionic liquid includes an anion having a donor number of 9 or less as determined from a half-wave potential of a noble metal.