Synthesis and reaction mechanism of 3 V LiMnO2

LiMnO2 with orthorhombic structure (Pm2m) was synthesized by hydro-thermal method using gamma-MnOOH and lithium hydroxide as starting material. A proc ess for the synthesis was proceeded by an ion exchange reaction, obtaining 190 Ah/kg of reversible capacity in 2 h lithiation and 160 Ah/kg in half an hour lithiation. Investigation for the changes of host material on each st eps of lithiation process was carried out in view of crystal structure, che mical state of lithium and proton in connection with electrochemical behavi or. When the orthorhombic phase appeared, a spectrum of solid-echo proton-N MR (H-NMR) on gamma-MnOOH became diminished, while a spectrum of solid-echo lithium-NMR (Li-7-NMR) emerged with three different kinds signals which is accompanied by spinning side band at around 37 ppm, 74 ppm and 1, ppm resp ectively. As longer lithiation in process, the ratio of intensity of each p eaks was changing, implying an occupation of lithium site might be changed in process. After cycling test on LiMnO2, it was hard to have a look of phe nomenon of spinel frame transition which might be seen in spinel material a t low temperature synthesis showing chemical shift of Li-NMR at around 600 ppm. We have tried to elucidate the mechanism of ion exchange reaction and also propose a method to enhance a rate for the process effectively in a sh ort time. (C) 1999 Elsevier Science S.A. All rights reserved.