Irreversible morphological changes of a graphite negative-electrode at high potentials in LiPF6-based electrolyte...

Area of Science:

• Electrochemistry
• Materials Science
• Surface Chemistry

Background:

• Graphite is a common anode material in lithium-ion batteries.
• Electrolyte degradation impacts battery performance and lifespan.
• Understanding graphite degradation is crucial for developing stable battery technologies.

Purpose of the Study:

• To investigate the degradation mechanism of graphite negative-electrodes in LiPF6-based electrolyte solutions.
• To elucidate the formation mechanisms of pits and fine particles on graphite surfaces.
• To utilize highly oriented pyrolytic graphite (HOPG) as a model electrode for detailed surface analysis.

Main Methods:

• In situ atomic force microscopy (AFM) to observe surface morphology changes.
• Spectroscopic analysis including X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to characterize fine particles.
• Electrochemical cycling in LiPF6-based and LiClO4-based electrolyte solutions.

Main Results:

• Pitting initiated on the HOPG basal plane around 1.75 V vs. Li(+)/Li during cathodic scanning.
• Fine particle formation was observed on the HOPG basal plane terraces at approximately 1.5 V vs. Li(+)/Li.
• The formation of pits and fine particles was successfully reproduced by adding a component to a LiClO4-based electrolyte.

Conclusions:

• The study proposes specific formation mechanisms for pits and fine particle layers on graphite electrodes.
• These findings provide insights into graphite anode degradation in lithium-ion batteries.
• The use of HOPG as a model system facilitates a deeper understanding of fundamental degradation processes.