EX-SITU AND IN-SITU CHARACTERIZATIONS OF THE LI REMOVAL FROM THE ANTIFLUORITE Li_5FeO_4

摘要

In order to boost the capacity of the lithium ion batteries,rncathode materials that can cycle with more than one lithium (Li) ionrnper transition metal (TM) ion are being intensively investigated. Thernantifluorite family of Li_8O_4 (4Li_2O unit cells) is an interestingrnstructure to host a high Li/TM ratio since the transition metal ionsrncan substitute part of the tetrahedral Li ions. A representativernmaterial is Li_5FeO_4 (LFO), with one Fe~(3+) ion replacing onerntetrahedral Li~+ ion and creating two vacancies. This material isrncapable of providing a Li/Fe ratio of five or about 867mAh/grncapacity in theory. Initial study of LFO has yielded intriguing resultsrnthat more than 4 Li ions can be extracted at two plateaus at about 3.5rnV and 4.0V, with capacity higher than 700mAh/g (Fig.1). Inrnaddition, in order to access all lithium ions, it is expected that O_2 isrnreleased when more than 2 Li ions are extracted from the LFO. SuchrnO_2 releasing reaction inspires a new concept to design a hybrid Lirnion/Li-O_2 cell employing dual-functioning electrodes/electrocatalystsrnthat are capable of releasing Li ion and O_2 during charging, andrnproducing Li_2O-metal oxide compounds during discharging.