Highly Reversible Conversion-Type CoSn₂ Cathode for Fluoride-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• All-solid-state fluoride-ion batteries (FIBs) offer high energy density and safety.
• Current challenges for FIBs include low fluoride ion conductivity and poor cycle stability in pure metal cathodes, hindering low-temperature operation.

Purpose of the Study:

• To develop a novel conversion-type cathode material for all-solid-state FIBs.
• To overcome the limitations of pure metal cathodes for improved low-temperature performance and cycle stability.

Main Methods:

• Synthesis and characterization of a cobalt-tin intermetallic alloy (CoSn2) as a conversion-type cathode.
• Electrochemical testing of the CoSn2 cathode in all-solid-state FIBs at various temperatures.
• Analysis of the charge-discharge mechanisms and structural evolution of the cathode material.

Main Results:

• The CoSn2 cathode achieved a discharge capacity of 229 mAh g-1 after 250 cycles at 60°C.
• During charging, CoSn2 decomposes into CoF2 and SnF2 nanocrystals, forming a nanoscale SnF2 network that enhances fluoride ion conduction.
• The cathode exhibits a highly reversible redox reaction, merging back into the CoSn2 phase during discharge, ensuring high cycle stability.

Conclusions:

• The CoSn2 intermetallic alloy is a promising cathode material for all-solid-state FIBs, enabling efficient operation at lower temperatures.
• The nanoscale structure and reversible conversion mechanism of CoSn2 significantly improve ionic conductivity and cycle life.
• This research paves the way for enhanced performance of all-solid-state FIBs in demanding temperature conditions.