Moisture-Controlled Electrolyte Engineering Enables Durable Calcium-Ion Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Calcium-ion batteries (CIBs) are promising alternatives to lithium-ion batteries due to calcium's abundance and high volumetric capacity.
• However, electrolyte instability and sensitivity to moisture hinder CIB development.

Purpose of the Study:

• To systematically examine Ca(ClO4)2 and Ca(PF6)2 electrolytes for CIBs.
• To identify optimal solvents and develop stringent dehydration methods to overcome electrolyte instability.
• To evaluate the electrochemical performance of moisture-controlled electrolytes in CIBs.

Main Methods:

• Systematic examination of Ca(ClO4)2 and Ca(PF6)2 electrolytes.
• Solvent selection focusing on acetonitrile (ACN) and carbonate-based solvents.
• Development of advanced dehydration techniques using 3 Å molecular sieve (MS3A) and vacuum drying to achieve parts-per-million (ppm) moisture levels.
• Electrochemical testing of Prussian blue (PB) half cells and PB-hard carbon full cells.

Main Results:

• Acetonitrile (ACN) demonstrated superior performance as a solvent for reversible Ca2+ electrochemistry compared to carbonate solvents.
• Optimized dehydration procedures reduced electrolyte moisture to ppm levels, significantly enhancing electrochemical performance.
• Prussian blue (PB) half cells achieved reversible capacities up to ~95 mAh g-1.
• PB-hard carbon full cells with dried Ca(ClO4)2 electrolytes exhibited stable cycling over 240 cycles, with ~99% Coulombic efficiency and ~17% capacity loss.

Conclusions:

• A moisture-controlled electrolyte is crucial for enabling practical and stable calcium-ion batteries.
• The developed dehydration method effectively stabilizes electrolytes, paving the way for high-performance CIBs.
• This research addresses key challenges in CIB technology, promoting their viability as next-generation energy storage solutions.