Electronic structure-driven sodiophilicity enables stable anode-free sodium batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anode-free sodium metal batteries (AFSBs) promise high energy density and low cost.
• Key limitations include low Coulombic efficiency and capacity decay due to irreversible sodium loss.
• Sodium nucleation and growth on current collectors critically impact AFSB performance and safety.

Purpose of the Study:

• To identify a descriptor for governing sodium nucleation and growth on current collectors.
• To engineer a stable interface for uniform and reversible sodium deposition in AFSBs.
• To enhance the cycle life and energy density of AFSBs.

Main Methods:

• Utilized the d-band center (εd) of collector surfaces as an electronic structure descriptor.
• Performed experimental tests and computational calculations to establish a relationship between εd and sodium nucleation overpotential.
• Engineered a TiO2 interphase layer on current collectors.

Main Results:

• A volcano-type relationship was observed between the d-band center and sodium nucleation overpotential.
• An intermediate εd was found to balance sodium binding and diffusion for uniform deposition.
• The engineered TiO2 interphase enabled 4000 stable cycles with 99.82% average Coulombic efficiency.
• Achieved high energy density (325 Wh/kg) in AFSBs and pouch cells.

Conclusions:

• The d-band center is a unifying descriptor for sodium-related behaviors in AFSBs.
• Optimizing the d-band center through interface engineering is crucial for stable sodium metal batteries.
• The developed framework offers a generalizable approach for designing interfaces in anode-free battery systems.