Electrolyte Solvation Engineering Stabilizing Anode-Free Sodium Metal Battery With 4.0 V-Class Layered Oxide Cathode

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Anode-free sodium metal batteries (AFSMBs) offer high energy density but face challenges with electrolyte and interfacial instability, particularly at extreme temperatures.
• Existing electrolytes struggle to maintain stable interfaces at high voltages and across wide temperature ranges (-40°C to 60°C).

Purpose of the Study:

• To develop an advanced electrolyte design strategy for stabilizing anode-free sodium metal batteries under demanding conditions.
• To improve the electrochemical performance and cycle life of high-voltage sodium-based batteries.

Main Methods:

• Electrolyte solvation engineering was employed to create a weakly solvating anion-stabilized (WSAS) electrolyte.
• The strategy balanced Na+-solvent and Na+-anion interactions to promote contact ion pairs (CIPs) and aggregates (AGGs) at the interface.
• Performance was evaluated using 4.0 V-class layered oxide cathodes and industrial multi-layer anode-free pouch cells across a wide temperature range.

Main Results:

• The WSAS electrolyte facilitated the formation of a uniform and stable interfacial layer, enabling highly stable cycling of 4.0 V-class layered oxide cathodes from -40°C to 60°C.
• Excellent reversibility of Na plating/stripping was achieved with an ultrahigh average Coulombic efficiency (CE) of 99.89%.
• Industrial anode-free pouch cells demonstrated 80% capacity retention after 50 cycles and maintained 74.3% capacity at -30°C.

Conclusions:

• The WSAS electrolyte design effectively addresses interfacial instability in anode-free sodium metal batteries at extreme temperatures.
• This breakthrough significantly advances the development of high-energy-density sodium batteries for practical applications.