Cathode materials for 5V lithium batteries
Complex spinel-structure oxides based on Li2MM'3O8 and LiMM'O4 have been systematically investigated on the basis of solid state chemistry and thermodynamics, and are found to constitute a novel family of cathode materials for 5 V lithium batteries. We have targeted lithium cathode materials that operate over 5 V, linked to large capacity and good cycling stability. The spinels prepared by solid state synthesis have been characterised using powder X-ray and neutron diffraction, impedance measurements, thermal analyses, magnetic measurements, XANES spectroscopy, Mossbauer spectroscopy and electrochemical measurements. In a single lithium cell, Li2CoMn3O8 and LiCoMnO4 are shown to be the first cathode materials to operate at discharge voltages over 5 V; Li2FeMn3O8 operates at a discharge plateau commencing at 5 V and centred on 4.9 V, offering potentially great economic and environmental advantages as a lithium cathode. LiCoMnO4 exhibits a discharge capacity of ca. 95 mAhg-1 at a long plateau centred on 5.0 V in a cell, Li/LiPF6, propylene carbonate / LiCoMnO4, and therefore has superior energy density to LiMn2O4, the cathode material used in state-of-the-art cells. This renders LiCoMnO4 potentially very attractive as a cathode material in practical 5 V lithium battery systems.