Li2O Removal from Li5FeO4: A Cathode Precursor for Lithium-Ion Batteries

Lithium has been extracted both electrochemically and chemically from the defect antifluorite-type structure, Li5FeO4 (5Li2O·Fe2O3). The electrochemical data show that four lithium ions can be removed from Li5FeO4 between 3.5 and 4.5 V. vs Li0. X-ray absorption spectroscopy (XAS) data of electrochemically delithiated samples show evidence of some Fe3+ to Fe4+ oxidation during the initial charge. On the other hand, XAS data of chemically delithiated samples show no evidence of Fe3+ to Fe4+ oxidation, but rather a change in coordination of the Fe3+ ions from tetrahedral to octahedral coordination, suggesting that lithium extraction from Li5FeO4 is accompanied predominantly by the release of oxygen, the net loss being lithia (Li2O); the residual lithium-iron-oxide product has a Fe2O3-rich composition. The high lithium content in Li5FeO4 renders it an attractive cathode precursor for loading the graphite (C6) anode of lithium-ion electrochemical cells with sufficient lithium to enable the discharge of a charged component in the parent cathode, Li1.2V3O8, as well as the residual Fe2O3-rich component. The electrochemical behavior of C6/Li5FeO4−Li1.2V3O8 lithium-ion cells is compared to C6/Li2MnO3−Li1.2V3O8 cells containing a layered Li2MnO3 (Li2O·MnO2) cathode precursor with a lower Li2O content, from which lithia can be extracted at higher potentials, typically >4 V vs metallic lithium. The ability to remove Li2O electrochemically from metal oxide host structures with a high lithium content, such as Li5FeO4, has implications for Li-air cells.