Chemical vs. electrochemical solid electrolyte interphase formation in potassium-ion batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Potassium-ion batteries (KIBs) are a promising alternative to lithium-ion technology due to abundant materials and enhanced safety.
• KIBs offer potential for low-cost electric vehicles and grid storage, but limited cycle life hinders adoption.
• Solid electrolyte interphase (SEI) instability is a primary cause of capacity fade in KIBs.

Purpose of the Study:

• To investigate the differences in SEI formation pathways on potassium metal and graphite electrodes.
• To understand how electrolyte composition and formation method influence SEI characteristics.
• To provide insights for designing electrolytes that enhance KIB stability and cycle life.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) was used to analyze SEI chemistry on different electrode materials.
• Four-dimensional scanning transmission electron microscopy (4D-STEM) provided structural information.
• SEI formation was studied on potassium metal, graphite, and inert electrodes using two distinct KFSI-based electrolytes.

Main Results:

• Distinct SEI chemical compositions and structures were observed between potassium metal and graphite electrodes.
• The formation pathway (chemical vs. electrochemical) significantly impacts SEI properties.
• Electrolyte formulation (G4 vs. 13-DX) influences SEI stability and chemistry.

Conclusions:

• The SEI formed on potassium metal is not fully representative of the SEI formed on graphite in KIBs.
• Understanding SEI formation mechanisms is critical for optimizing electrolyte design for KIBs.
• This research offers guidance for developing more stable electrolytes to improve KIB cycle life.