Electrolyte Oxidation Pathways in Lithium-Ion Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Electrolyte decomposition in lithium-ion batteries limits device lifetime and performance.
• Understanding complex decomposition mechanisms is challenging due to varied compositions and operating conditions.

Purpose of the Study:

• To investigate electrolyte oxidation and reduction mechanisms at multiple cell voltages.
• To elucidate the dominant decomposition pathways in LiCoO2-based cells.

Main Methods:

• Utilized *operando* pressure measurements, solution Nuclear Magnetic Resonance (NMR), and electrochemical techniques.
• Employed two-compartment LiCoO2/Li cells with a lithium-ion conducting glass-ceramic separator to isolate electrode reactions.

Main Results:

• Chemical oxidation, initiated by reactive oxygen release from LiCoO2 at high states-of-charge (onset ~4.7 V vs Li/Li+), is the primary decomposition process at the positive electrode.
• Identified soluble electrolyte decomposition products formed at both electrodes.
• Established a detailed reaction scheme rationalizing the observed species formation.

Conclusions:

• Electrolyte decomposition at the positive electrode is intrinsically linked to the active material's surface reactivity and oxygen release.
• Findings provide critical insights for mitigating degradation in high-voltage LiCoO2 and nickel-containing cathode materials (e.g., NMCs).
• Understanding these mechanisms is key to enhancing the longevity and performance of advanced lithium-ion batteries.