Borohydride and halide dual-substituted lithium argyrodites

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sulfide solid electrolytes, particularly lithium argyrodites, are leading candidates for all-solid-state batteries due to their high ionic conductivity and processability.
• Developing novel solid electrolytes with enhanced performance is critical for advancing battery technology beyond current lithium-ion limitations.

Purpose of the Study:

• To synthesize and characterize novel borohydride/halide dual-substituted argyrodite-type solid electrolytes.
• To investigate the ionic conductivity, electrochemical stability, and performance of these electrolytes in all-solid-state batteries.

Main Methods:

• Synthesis of Li_7-PS_6-(BH₄)X electrolytes (X = Cl, Br, I) using a two-step ball-milling method without post-annealing.
• Ionic conductivity measurements using electrochemical impedance spectroscopy.
• Electrochemical performance evaluation in Li symmetric cells and all-solid-state battery configurations.

Main Results:

• The composition Li_5.35PS_4.35(BH₄)_1.15Cl_0.5 achieved the highest ionic conductivity of 26.1 mS cm^-1 after low-temperature sintering.
• Stable lithium plating/stripping cycling (>2,000 hours) and a high critical current density (2.1 mA cm^-2) were observed in Li symmetric cells.
• An initial coulombic efficiency of 86.4% was achieved in an all-solid-state battery using this electrolyte and a pure lithium anode.

Conclusions:

• Borohydride/halide dual substitution in argyrodite electrolytes significantly enhances ionic conductivity by increasing Li vacancies and site disorder.
• The developed electrolytes show promising stability for lithium metal anodes, crucial for high-energy-density solid-state batteries.
• Despite limited thermal stability, the wide compositional range and high ionic conductivity highlight their potential for practical all-solid-state battery applications.