Direct Evaluation of the Electrode/Electrolyte Interface with Additives by Single-Particle Electrochemical...

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Controlling interfacial reactions is key for high-performance lithium-ion batteries (LIBs).
• Electrolyte additives form protective interphase films, but observing their formation on single active materials is difficult due to composite electrode structures.
• Single-particle electrochemical measurement (SPEM) offers a novel approach to study these phenomena.

Purpose of the Study:

• To investigate the electrochemical and resistance changes during *in-situ* additive introduction on a single LiCoO2 particle (LCO-SP).
• To demonstrate the capability of SPEM in observing interphase layer formation at the electrode/electrolyte interface on a single-particle level.

Main Methods:

• Utilized single-particle electrochemical measurement (SPEM) with an open-type cell.
• Employed AC impedance spectroscopy to analyze resistance components.
• Introduced LiPO2F2 additive *in-situ* to a charged LCO-SP in an ethylene carbonate-LiN(SO2F)2 electrolyte.

Main Results:

• Additive-free LCO-SP showed a single asymmetric semicircular arc in impedance spectra, representing internal, charge transfer, and interphase resistances.
• Additive presence altered the impedance spectra, indicating changes in the charge transfer process.
• *In-situ* additive introduction led to two semicircular arcs and increased low-frequency resistance, confirming interphase layer growth on the LCO-SP.

Conclusions:

• SPEM effectively enables direct and precise observation of resistance behavior at the electrode/electrolyte interface on a single-particle scale.
• This technique provides valuable insights into the *in-situ* formation and impact of interphase layers during additive introduction.
• SPEM is a powerful tool for understanding and optimizing LIB performance by studying interfacial phenomena.