Interdependence of Support Wettability - Electrodeposition Rate- Sodium Metal Anode and SEI Microstructure

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Anode-free sodium metal batteries (AF-SMBs) offer high energy density but face challenges with sodium metal anode stability.
• The current collector's surface chemistry and sodium electrodeposition conditions critically influence the formation of the solid electrolyte interphase (SEI).

Purpose of the Study:

• To investigate the effect of sodiophilic (Na2Te) versus sodiophobic (Cu) current collector supports on sodium metal microstructure and SEI formation.
• To analyze the impact of electrodeposition rate on sodium metal and SEI characteristics under industrially relevant conditions (6 mAh cm−2, 0.5–3 mA cm−2).

Main Methods:

• Combined synchrotron X-ray nanotomography and grazing-incidence wide-angle X-ray scattering (GIWAXS) for detailed microstructural analysis.
• Cryogenic ion beam (cryo-FIB) microscopy for high-resolution imaging of the SEI.
• Mesoscale modeling to understand the SEI's role in electrodeposit growth and electrochemical stability.

Main Results:

• Significant differences observed in sodium film morphology, internal porosity, and crystallographic preferred orientation (e.g., (110) vs. (100) and (211)) based on support chemistry and deposition rate.
• Na2Te supports resulted in a higher prevalence of sodium fluoride (NaF) in the SEI, whereas Cu supports showed more sodium hydride (NaH) and sodium hydroxide (NaOH).
• Preferred orientation of sodium crystallites is thickness-dependent due to competitive grain growth.

Conclusions:

• Current collector chemistry and electrodeposition rate are crucial parameters for controlling sodium metal anode behavior in AF-SMBs.
• The SEI's ionic conductivity and morphology, influenced by these parameters, play a key role in regulating electrodeposit growth and preventing electrochemical instability.