Understanding and Suppressing the Destructive Cobalt(II) Species in Graphite Interphase

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Cobalt species dissolution from LiCoO2 cathodes causes lithium-ion battery performance fade, particularly at high voltage and temperature.
• The established mechanism involves Co2+ deposition on graphite anodes, disrupting the solid electrolyte interphase (SEI).

Purpose of the Study:

• To investigate the speciation and behavior of dissolved cobalt on graphite anodes.
• To elucidate the role of cobalt species in electrolyte decomposition and interphase degradation.
• To develop a strategy for mitigating cobalt-induced battery failure.

Main Methods:

• Electrochemical analysis of LiCoO2-based lithium-ion cells.
• Surface characterization of graphite anodes.
• Electrolyte analysis and performance testing with a novel film-forming additive.

Main Results:

• Dissolved cobalt exists as both Co0 and Co2+ on the graphite anode.
• Co0 species, formed during lithiation, can be reoxidized to Co2+ and exhibit higher catalytic activity for carbonate electrolyte decomposition than Co2+.
• A ~4 nm interphase engineered using 3-sulflone additive effectively suppressed cobalt-induced degradation.

Conclusions:

• The dual-state nature (Co0 and Co2+) and catalytic activity of dissolved cobalt significantly contribute to battery failure.
• Engineered interphases provide an effective strategy to prevent cobalt-induced degradation of graphite anodes.
• This work offers insights into failure mechanisms in cobalt-containing cathodes and guides future electrolyte design for enhanced battery stability.