Molecular Wedge Reconstructing the Solvation Structure for Low-Temperature Ah-Level Anode-Free Sodium Metal...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anode-free sodium metal batteries (AFSMBs) offer high energy density but suffer from poor low-temperature performance due to sluggish kinetics.
• Practical, all-climate applications of AFSMBs are hindered by their limited operational temperature range.

Purpose of the Study:

• To develop a novel electrolyte design strategy for wide-temperature operation of high-energy-density AFSMBs.
• To enhance the kinetics of sodium plating/stripping and improve cycling stability at low temperatures.

Main Methods:

• A molecular wedging strategy was employed for electrolyte design, utilizing bulky cosolvents to disrupt the solvation structure.
• The electrolyte's effect on sodium deposition/dissolution and interfacial chemistry was investigated across a temperature range of 25°C to -40°C.
• Performance of AFSMBs and Ah-level pouch cells with the new electrolyte was evaluated.

Main Results:

• The molecular wedging electrolyte enabled highly reversible sodium plating/stripping with 99.98% Coulombic efficiency and low overpotential (<30 mV) from 25°C to -40°C.
• High-cathode-loading AFSMBs demonstrated stable cycling (>205 cycles) at -40°C with 93 mAh g^-1 discharging capacity.
• Ah-level pouch cells achieved high energy densities of 170-184 Wh kg^-1 and stable cycling at -40°C.

Conclusions:

• The molecular wedging strategy effectively reconstructs solvation structure, enabling wide-temperature function in AFSMBs.
• This approach overcomes low-temperature limitations, paving the way for practical, all-climate AFSMB applications.
• The developed electrolyte is crucial for advancing high-energy-density, cost-effective sodium metal batteries.