Copper-doped metal-organic framework-74 solid-state electrolytes for high performance all-solid-state sodium metal...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Rechargeable solid sodium metal batteries offer high energy density but suffer from poor Na+ transport and limited lifespan.
• Metal-organic frameworks (MOFs), like Mg-MOF-74, show promise as solid-state electrolytes due to their porous structure, but pristine versions have low Na+ conductivity.
• Sluggish ion movement in Mg-MOF-74 limits its effectiveness as a solid-state electrolyte for sodium batteries.

Purpose of the Study:

• To enhance Na+ transport dynamics and electrochemical stability in solid-state electrolytes for sodium metal batteries.
• To develop and investigate bimetallic MOFs as improved solid-state electrolytes.
• To overcome the limitations of pristine Mg-MOF-74 in solid sodium battery applications.

Main Methods:

• Synthesis of a series of bimetallic MOFs, specifically Cu2Mg8-MOF-74, by doping Mg-MOF-74 with copper.
• Characterization of the synthesized MOF electrolytes for Na+ transport properties and electrochemical stability.
• Density Functional Theory (DFT) calculations to understand anion anchoring mechanisms.
• Fabrication and testing of Na3V2(PO4)3|Cu2Mg8-MOF-74|Na battery cells.

Main Results:

• The bimetallic Cu2Mg8-MOF-74 electrolytes exhibited significantly improved Na+ transport compared to pristine Mg-MOF-74.
• Cu2Mg8-MOF-74 demonstrated enhanced anion (ClO4-) anchoring capabilities due to bimetallic sites, as confirmed by DFT.
• Achieved ionic conductivity of 3.18 × 10^-3 S cm^-1 and a Na+ transference number of 0.86 at room temperature.
• Na3V2(PO4)3|Cu2Mg8-MOF-74|Na cells delivered a high specific capacity of 104.5 mAh g^-1 at 1C with 91% capacity retention.

Conclusions:

• The developed bimetallic Cu2Mg8-MOF-74 is a highly effective solid-state electrolyte for rechargeable sodium metal batteries.
• Doping Mg-MOF-74 with copper successfully enhances Na+ conductivity and electrochemical stability.
• This study presents a viable strategy for optimizing MOF materials for advanced sodium battery applications.