Lithium Iron Chloride Battery Research
Scientists are looking beyond familiar metal-centered chemistries to build safer and more capable rechargeable batteries. A team led by Professor Ru-Shi Liu in the Department of Chemistry at National Taiwan University found converging experimental and computational evidence for chlorine anion redox in lithium iron chloride (Li₂FeCl₄).
The study helps explain structural and electronic changes that accompany charging in this halide cathode. Researchers from the National Synchrotron Radiation Research Center in Taiwan and Nagoya Institute of Technology in Japan collaborated on the project. Their findings were published in the journal Small.
All-Solid-State Cell Assembly
The research team built an all-solid-state cell using Li₂FeCl₄ as the cathode. The setup included a Li₃InCl₆ solid electrolyte, a Li₁₀GeP₂S₁₂ interlayer, and a lithium-indium alloy anode.
Electrochemical measurements identified two distinct oxidation features. These features appeared near 3.8 and 4.2 V versus Li⁺/Li.
Chlorine Contributes to the Higher-Voltage Oxidation Process
The lower-voltage process linked primarily to Fe²⁺/Fe³⁺ oxidation. The higher-voltage feature indicated an additional contribution involving chlorine.
To investigate the origin of the second process, the team combined X-ray photoelectron spectroscopy and X-ray absorption spectroscopy with density functional theory calculations. These measurements showed changes in chlorine’s electronic state upon charging.
Chlorine-Derived Nonbonding Orbitals Contribute to Charge Compensation
Calculations of the partial density of states and crystal orbital Hamilton population identified occupied, chlorine-derived nonbonding orbitals. These electronic states can contribute to charge compensation when electrons are removed.
Battery Research Questions
Why are researchers looking at anions in battery cathodes?
Conventional cathodes rely heavily on transition metals for charge. Drawing additional charge from negatively charged atoms like oxygen, sulfur, and chlorine offers a promising route for safer and more capable rechargeable batteries.
What materials made up the test cell?
The all-solid-state cell utilized a Li₂FeCl₄ cathode, a Li₃InCl₆ solid electrolyte, a Li₁₀GeP₂S₁₂ interlayer, and a lithium-indium alloy anode.
What did the spectroscopic and computational tests reveal?
The combination of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and density functional theory calculations showed shifts in chlorine’s electronic state and identified nonbonding orbitals capable of charge compensation during charging.
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