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

Abstract

Lithium has been extracted both electrochemically and chemically from the defect antifluorite-type structure, Li 5 FeO 4 (5Li 2 O·Fe 2 O 3 ). The electrochemical data show that four lithium ions can be removed from Li 5 FeO 4 between 3.5 and 4.5 V. vs Li 0 . X-ray absorption spectroscopy (XAS) data of electrochemically delithiated samples show evidence of some Fe 3+ to Fe 4+ oxidation during the initial charge. On the other hand, XAS data of chemically delithiated samples show no evidence of Fe 3+ to Fe 4+ oxidation, but rather a change in coordination of the Fe 3+ ions from tetrahedral to octahedral coordination, suggesting that lithium extraction from Li 5 FeO 4 is accompanied predominantly by the release of oxygen, the net loss being lithia (Li 2 O); the residual lithium-iron-oxide product has a Fe 2 O 3 -rich composition. The high lithium content in Li 5 FeO 4 renders it an attractive cathode precursor for loading the graphite (C 6 ) anode of lithium-ion electrochemical cells with sufficient lithium to enable the discharge of a charged component in the parent cathode, Li 1.2 V 3 O 8, as well as the residual Fe 2 O 3 -rich component. The electrochemical behavior of C 6 /Li 5 FeO 4 −Li 1.2 V 3 O 8 lithium-ion cells is compared to C 6 /Li 2 MnO 3 −Li 1.2 V 3 O 8 cells containing a layered Li 2 MnO 3 (Li 2 O·MnO 2 ) cathode precursor with a lower Li 2 O content, from which lithia can be extracted at higher potentials, typically >4 V vs metallic lithium. The ability to remove Li 2 O electrochemically from metal oxide host structures with a high lithium content, such as Li 5 FeO 4, has implications for Li-air cells.