Operando insights into ammonium-mediated lithium metal stabilization: surface morphology modulation and enhanced SEI...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Lithium-ion batteries (LiBs) face limitations in specific energy and power, necessitating advanced anode materials.
• Lithium metal anodes offer high capacity but suffer from dendrite growth, leading to short circuits and cell failure.

Purpose of the Study:

• To investigate the electrochemical behavior of ammonium hexafluorophosphate (NH4PF6) as a protic additive in carbonate-based electrolytes for lithium metal anodes.
• To elucidate the functional mechanism of NH4PF6 in stabilizing lithium deposition and preventing dendrite formation.

Main Methods:

• Operando confocal Raman spectroscopy
• In situ optical microscopy
• X-ray photoelectron spectroscopy (XPS)

Main Results:

• The ammonium cation (NH4+) chemically modifies the lithium metal anode-electrolyte interphase.
• Formation of an N-rich solid electrolyte interphase (SEI) and electrochemical pitting of the lithium surface were observed.
• Stable lithium deposition and stripping were achieved by decreasing local current density, effectively limiting dendritic growth.

Conclusions:

• NH4PF6 acts as a functional additive, promoting a stable SEI layer and controlled lithium plating.
• This approach mitigates dendrite formation, enhancing the safety and cycle life of lithium metal batteries.
• The findings pave the way for practical applications of high-energy lithium metal anodes in rechargeable cells.