Fluoride modification of materials, whether through doping or anion substitution in cathode intercalation materials or incorporation of LiF at anode/cathode interfaces, is emerging as a highly promising strategy to impart desirable properties such as higher surface exchange kinetics, improved stability, and precise structural modification of Li storage materials. For example, the success of a truly cycleable Li anode will rely upon the ability to design improved interfacial stability at the solid electrolyte interphase (SEI) and support homogeneous Li transport to suppress or avoid dendrites, a process where LiF has been suggested to play an important role. Meanwhile, cathode materials, ranging in complexity from binary oxides to cation-disordered rock-salt phases, have been shown recently to benefit strongly from fluoride incorporation or substitution of oxide anions, respectively. There are numerous challenges, however, in rationally developing classes of fluoride-based materials owing to the intransigence of LiF as a typical precursor, and/or the toxicity of many alternative fluorine-containing precursors in the liquid or gas phase. Such challenges have arguably acted as a bottleneck for exploring the broad phase space of fluoride-modified materials. In this talk, we report methodologies developed recently in our group to manipulate fluoride-forming reactions, and specifically those that form LiF, for modifying the interfaces and bulk composition of Li storage materials. We focus on strategies to coat conformal, electronically-connected LiF on transition metal oxides using electrochemical methods in which precursors in the electrolyte are activated by electron transfer, controllably liberating F-. We show that careful manipulation of LiF morphology, such as its quantity, microstructure, and three-dimensionality can be achieved by modulating the cell parameters, including electrolyte chemistry, rate, depth-of-discharge, and temperature during the LiF formation step. We discuss how these parameters influence the subsequent effectiveness of fluoride incorporation into the bulk oxide phases upon charge and subsequent cycling, which fundamentally alters the electrochemical properties of the cathode. The potential of electrochemical “soft synthesis” on facilitating access to new phases for Li storage will be discussed.

In situ fluoride modification of Li storage materials for advanced battery chemistries

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.