Tailoring Chloride Solid Electrolytes for Reversible Redox.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Solid-state electrolytes are crucial for next-generation batteries, offering higher energy density and safety.
• Current solid-state batteries face limitations due to inactive solid-state electrolytes acting as dead weight in cathodes, reducing overall energy density.
• Achieving sufficient ionic percolation in solid-state battery cathodes requires high weight fractions of the electrolyte.

Purpose of the Study:

• To design and synthesize novel redox-active solid-state electrolytes.
• To investigate the Na+ intercalation mechanisms in modified solid-state electrolytes.
• To enhance the energy density and electrochemical performance of solid-state battery cathodes.

Main Methods:

• Aliovalent substitution of Zr4+ with redox-active M5+ (Nb or Ta) in Na2ZrCl6 to form Na2-xMxZr1-xCl6 solid solutions.
• Electrochemical characterization of the synthesized solid solutions and end-member NaMCl6 materials.
• Fabrication and testing of cathode composites using the novel electrolytes paired with oxide cathode materials.

Main Results:

• Synthesized Na2-xMxZr1-xCl6 solid solutions exhibit high ionic conductivities and active sites for Na+ storage.
• Niobium- and tantalum-containing chlorides operate at high electrochemical potentials (2.2-2.8 V vs Na9Sn4).
• Cathode composites using these redox-active electrolytes showed an 83-102% increase in energy density and 39-81% improvement in areal discharge capacity.

Conclusions:

• Redox-active solid-state electrolytes can be designed by incorporating active cations into the electrolyte structure.
• This approach overcomes the dead weight limitation of inactive electrolytes, significantly boosting battery performance.
• The study opens new avenues for discovering advanced solid-state electrolytes and designing high-performance solid-state batteries.