A low-cost, lithium-rich zirconium-based oxyhalide solid electrolyte featuring an efficient ion transport structure

Area of Science:

• Materials Science
• Electrochemistry
• Solid-state ionics

Background:

• Halide solid electrolytes are crucial for high-performance all-solid-state lithium batteries (ASSLBs) due to their stability and compressibility.
• Low-cost Li₂ZrCl₆ shows promise but suffers from low room-temperature ionic conductivity.
• Improving ionic conductivity is key to unlocking the potential of halide solid electrolytes for ASSLBs.

Purpose of the Study:

• To enhance the ionic conductivity of Li₂ZrCl₆ by incorporating lithium and oxygen.
• To investigate the structural and electrochemical properties of the modified electrolyte.
• To evaluate the performance of an all-solid-state lithium battery utilizing the novel electrolyte.

Main Methods:

• Incorporation of Li₂O into Li₂ZrCl₆ via high-energy ball milling to induce lithium enrichment and phase transition.
• Structural characterization and ionic conductivity measurements at 25 °C.
• Density Functional Theory (DFT) calculations to understand the mechanisms of conductivity enhancement.
• Fabrication and electrochemical testing of an all-solid-state lithium battery (ASSLB) with the new electrolyte.

Main Results:

• Synthesis of a monoclinic Li₆ZrCl₆O₂ electrolyte with a structure similar to Li₃ScCl₆, distinct from the trigonal phase.
• Achieved an ionic conductivity of 6.69 × 10⁻⁴ S cm⁻¹ at 25 °C.
• DFT calculations and experiments confirmed enhanced lithium concentration, crystal structure transformation, and optimized surface structure.
• The ASSLB demonstrated an initial coulombic efficiency of 84.85%, a discharge capacity of 204.58 mAh g⁻¹, and 93.5% capacity retention after 100 cycles.

Conclusions:

• Lithium enrichment and phase transition induced by Li₂O incorporation significantly improve the ionic conductivity of Li₂ZrCl₆.
• The synthesized Li₆ZrCl₆O₂ solid electrolyte shows excellent potential for developing high-performance ASSLBs.
• The study provides a viable strategy for optimizing halide solid electrolytes for next-generation energy storage.