Materials that undergo a conversion reaction with lithium (e.g., metal fluorides) often accommodate more than one Li atom per transition-metal, and are promising candidates for high-capacity electrodes for lithium batteries. However, little is known about the mechanisms involved in the conversion process, the origins of the large polarization during electrochemical cycling, and why some materials are reversible (FeF2) while others are not (CuF2). We investigated the conversion reaction of binary metal fluorides, FeF2 and CuF2, via a series of local and bulk probes to better understand the mechanisms underlying their contrasting electrochemical behavior. During the reaction with lithium, metallic iron nanoparticles (< 5nm) nucleate in close proximity to the converted LiF phase forming an interconnected bi-continuous network, which provides a pathway for electron transport through the insulating LiF media. In addition, the massive interface formed between the nanoscale solid phases provides a pathway for ionic transport during the conversion process.

Conversion electrodes for lithium batteries: Evolution of nanostructure during lithiation

243rd National Meeting (2012)

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