Li₂O removal from Li₅FeO₄: A cathode precursor for lithium-ion batteries

Lithium has been extracted both electrochemically and chemically from the defect antifiuorite-type structure, Li₅FeO₄ (5Li ₂O-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 Fe ³⁺ 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 (Li ₂O); the residual lithium-iron-oxide product has a Fe ₂O_3- rich composition. The high lithium content in Li ₅FeO₄ 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, Li_1.2V₃O₈, as well as the residual Fe₂O₃-rich component. The electrochemical behavior of C₆/Li₅FcO₄-Li_1.2V ₃O₈ lithium-ion cells is compared to C₆/Li ₂MnO₃-Li_1.2V₃O₈ 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 Li ₅FeO₄, has implications for Li-air cells.