Aqueous Li-ion battery enabled by halogen conversion-intercalation chemistry in graphite

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous lithium-ion batteries (ALIBs) offer enhanced safety but are limited by low energy densities.
• Water-in-salt electrolytes expand the electrochemical window of ALIBs to 3-4 volts.
• Current ALIBs suffer from low lithium intercalation capacities in transition-metal-oxide cathodes.

Purpose of the Study:

• To develop a high-capacity cathode material for ALIBs.
• To achieve higher energy densities in aqueous lithium-ion batteries.
• To explore novel electrochemical mechanisms beyond traditional intercalation.

Main Methods:

• Investigated halogen conversion-intercalation chemistry in graphite.
• Synthesized and characterized a composite electrode material (C3.5[Br0.5Cl0.5]).
• Assembled and tested a 4-volt-class aqueous Li-ion full cell with a passivated graphite anode.

Main Results:

• Achieved a specific capacity of 243 mAh/g for the composite electrode at 4.2 V vs. Li/Li+.
• Demonstrated reversible formation of a stage-I graphite intercalation compound in water-in-bisalt electrolyte.
• The full cell exhibited an energy density of 460 Wh/kg and ~100% Coulombic efficiency.

Conclusions:

• The novel anion conversion-intercalation mechanism significantly boosts ALIB energy density.
• This approach combines high energy conversion reactions with intercalation reversibility.
• The developed system offers a safer alternative for high-performance aqueous energy storage.