Fluoride-Ion Cell Core-Shell Electrodes for Stable Cycling
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Solution Overview
Problem
Existing fluoride-ion batteries face challenges with the stability and reliability of metal nanoparticles due to high surface energies, reactivity with electrolytes, and significant volume changes during electrochemical processes, leading to undesirable side-reactions and limited cycling stability.
Innovation Solution
The development of core-shell nanoparticles with a metal core surrounded by a metal halide or oxyhalide shell, which protects the active material from electrolyte reactions and accommodates volume changes, allowing for stable ion conduction and long-term cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If metal nanoparticles are used as electrode materials, then high surface energy and reactivity provide enhanced electrochemical activity, but they suffer from significant volume changes and side-reactions with electrolytes leading to poor cycling stability
Solution Approach 1:
A protective shell layer is introduced as an intermediary between the metal nanoparticle core and the electrolyte. This shell prevents direct contact and harmful side-reactions while allowing fluoride ion transport, thus maintaining electrochemical activity while improving cycling stability.
Solution Approach 2:
The protective shell is designed as a thin film structure that can accommodate the volume changes of the metal core during electrochemical cycling. This flexible shell structure prevents particle degradation while maintaining structural integrity over multiple cycles.
2Reliability
If solid-state fluoride-conducting electrolytes are used, then fluoride-ion batteries can operate with reversible fluoride exchange, but the limited conductivity requires operation above room temperature (e.g., 150°C)
Solution Approach 1:
The patent modifies the physical state parameter of the electrolyte from solid to liquid, which fundamentally changes the ionic conductivity characteristics. Liquid electrolytes provide higher fluoride ion conductivity at room temperature, eliminating the need for elevated operating temperatures while maintaining reversible fluoride exchange capability.
3Temperature
If liquid electrolytes with dissolved fluoride salts are used, then fluoride-ion batteries can operate at room temperature, but significant chemical reactivity between electrode materials and electrolyte reduces discharge reliability and capacity
Solution Approach 1:
The protective shell serves as an intermediary barrier between the electrode material and liquid electrolyte. It prevents harmful chemical reactions while permitting fluoride ion transport, thus enabling room temperature operation with maintained discharge reliability and capacity.
4Adaptability or versatility
If metal nanoparticles are used to accommodate volume changes, then electrochemical reactions can proceed, but high surface energy leads to undesirable side-reactions with electrolytes
Solution Approach 1:
The protective shell acts as an intermediary layer that physically separates the high-energy metal nanoparticle surface from the electrolyte, preventing side-reactions while allowing the nanoparticle to accommodate volume changes during electrochemical cycling.
Solution Approach 2:
The shell is designed as a flexible thin film that can stretch and contract to accommodate the volume changes of the metal core during charge-discharge cycles, while continuously preventing harmful electrolyte contact with the reactive metal surface.
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 core-shell structure enhances the stability and conductivity of fluoride-ion batteries, enabling reliable long-term cycling and improved performance at room temperature.
Implementation Method 1
allowing for stable ion conduction and long-term cycling
Implementation Method 2
accommodates volume changes, allowing for stable ion conduction and long-term cycling
Data Source
AI summary
A method of making core-shell and yolk-shell nanoparticles, and to electrodes comprising the same. The core-shell and yolk-shell nanoparticles and electrodes having the same are suitable for use in electrochemical cells, such as fluoride shuttle batteries. The shell may protect the metal core from oxidation, including in an electrochemical cell. In some embodiments, an electrochemically active structure includes a dimensionally changeable active material forming a particle that expands or contracts upon reaction with or release of fluoride ions. One or more particles are at least partially surrounded with a fluoride-conducting encapsulant and optionally one or more voids are formed between the active material and the encapsulant using sacrificial layers or selective etching. When the electrochemically active structures are used in secondary batteries, the presence of voids can accommodate dimensional changes of the active material.