Intercalation-type catalyst for non-aqueous room temperature sodium-sulfur batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Ambient-temperature sodium-sulfur (Na-S) batteries are promising alternatives to lithium-ion batteries due to high theoretical specific energy and abundant sulfur resources.
• A major challenge hindering practical Na-S battery application is the shuttle effect of sodium polysulfides.

Purpose of the Study:

• To develop a novel intercalation-conversion hybrid positive electrode material for ambient-temperature Na-S batteries.
• To address the sodium polysulfide shuttling issue and enhance battery performance and stability.

Main Methods:

• Coupling an intercalation-type catalyst, Molybdenum Ditelluride (MoTe2), with a conversion-type active material, sulfur.
• Vertically growing MoTe2 nanosheets on graphene flakes to create abundant catalytic sites.
• Assembling a composite positive electrode in a coin cell with excess sodium (Na).
• Utilizing in-situ synchrotron-based operando X-ray diffraction and ex-situ time-of-flight secondary ion mass spectrometry for mechanistic studies.

Main Results:

• Achieved a high discharge capacity of 1,081 mAh g^-1 (based on sulfur mass).
• Demonstrated excellent cycle stability with a capacity fade rate of 0.05% per cycle over 350 cycles at 0.1 C.
• Operated under demanding conditions: high sulfur loading (3.5 mg cm^-2) and lean electrolyte (7 μL mg^-1).
• Revealed the electrocatalytic mechanism of MoTe2 in sulfur redox reactions.

Conclusions:

• The developed MoTe2-sulfur hybrid electrode effectively suppresses polysulfide shuttling in Na-S batteries.
• This hybrid material demonstrates significant potential for high-performance, stable ambient-temperature Na-S battery applications.
• The study provides fundamental insights into the catalytic role of MoTe2 in Na-S battery chemistry.