Electrolyte-Dependent Sodium Plating for Anode-Free Na-Ion Batteries Studied by Operando Optical Microscopy

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Anode-free sodium ion batteries (SIBs) offer higher energy density and reduced cost by omitting anode host materials.
• Efficient sodium (Na) plating and stripping are critical challenges for anode-free SIBs.

Purpose of the Study:

• To evaluate different electrolyte classes for Na plating/stripping on a carbon-coated aluminum current collector.
• To assess the performance of anode-free SIBs using the most effective electrolyte.

Main Methods:

• Comparative analysis of carbonate-based, glyme-based, and localized high-concentration electrolytes.
• Electrochemical measurements across wide temperature and current ranges (-30°C to +60°C, 0.25-14 mA cm⁻²).
• Operando optical microscopy to study Na growth modes.

Main Results:

• Glyme-based electrolytes demonstrated superior Na plating/stripping with uniform crystalline deposition.
• Anode-free full cells with glyme-based electrolyte achieved 75.3% capacity retention over 400 cycles.
• Low initial areal capacity loss (IACL) of 0.14-0.16 mAh cm⁻² was observed.

Conclusions:

• Glyme-based electrolytes are highly effective for anode-free SIBs, enabling efficient Na plating/stripping.
• Anode-free SIBs with glyme-based electrolytes show potential for high energy density (projected 290 Wh/kg) and long cycle life.
• Commercially viable anode-free SIBs are feasible with optimized electrolytes and components.