Towards Solid-State Batteries Using a Calcium Hydridoborate Electrolyte

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Solid-state batteries offer safer and potentially cheaper alternatives to conventional lithium-ion batteries.
• Abundant elements like calcium are desirable for sustainable energy storage solutions.
• Developing efficient solid electrolytes is crucial for advancing solid-state battery technology.

Purpose of the Study:

• To report a new solid calcium hydridoborate electrolyte with high ionic conductivity.
• To investigate the structural properties facilitating ion transport.
• To demonstrate the electrochemical performance of the electrolyte in a solid-state battery cell.

Main Methods:

• Synthesis and characterization of the calcium hydridoborate electrolyte (Ca(BH4)2·2NH2CH3).
• Ionic conductivity measurements at various temperatures.
• Electrochemical cell fabrication and testing (Ca|electrolyte|Pt).
• Electrode surface analysis using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS).
• Three-electrode cell testing with CaₓSn and Sn electrodes for improved reversibility.

Main Results:

• The novel electrolyte exhibits high ionic conductivity (σ(Ca²⁺) ~10⁻⁵ S cm⁻¹ at 70°C).
• The material possesses an open, flexible structure with weak dihydrogen bonds, promoting Ca²⁺ ion migration.
• High ionic transport number (t_ion = 0.9916) and low electronic conductivity were confirmed.
• Reversible calcium plating and stripping were achieved in a three-electrode configuration.

Conclusions:

• The developed solid calcium hydridoborate electrolyte shows significant promise for solid-state batteries.
• Its properties enable efficient and stable calcium ion transport.
• This material contributes to the development of cheaper and safer electrical energy storage systems.