A MANGANESE OXYIODIDE CATHODE FOR RECHARGEABLE LITHIUM BATTERIES

The increasing demand for portable electronic devices is driving the d evelopment of compact lightweight batteries of high energy density(1). Lithium-ion batteries tend to be the systems of choice, as they offer higher energy densities and longer operational lifetimes than other r echargeable battery systems(1,2). But commercially available lithium-i on batteries make use of layered LiCoO2 cathodes(3,4), and the high co st and toxicity of cobalt therefore motivate the development of cheape r and environmentally benign cathode materials. In this regard, mangan ese oxides are attractive alternatives, and the spinel LiMn2O4 has bee n investigated intensively as a cathode(5,6); however, the fading on c ycling of its energy-storage capacity poses problems, More recently, a ttention has been focused on the synthesis of layered LiMnO2 as a cath ode material, but its cycling characteristics remain to be established (7-9). Here we report the synthesis and electrochemical performance of a new manganese oxide cathode, the oxyiodide Li1.5Na0.5MnO2.85I0.12. Our material exhibits a high reversible capacity of 260 mA h g(-1) in the range 1.5-4.3 V with excellent cycling characteristics. Furthermor e, the amorphous nature of the material (as determined by X-ray diffra ction) and smooth discharge behaviour may help to overcome the problem s associated with lattice distortions that have plagued manganese oxid es with more crystalline structures(5-9).