Neutron diffraction study of electrochemically delithiated LiMn2O4 spinel

Partially electrochemically delithiated LiMn2O4 has been studied by a combi nation of in situ X-ray and ex situ neutron diffraction to help shed furthe r light on structural phenomena in the >4 V range. LixMn2O4 samples were ex tracted from charged half-cells and their structures refined by the Rietvel d method. At ca. 4.1 V, a spinel-phase of composition Li0.74Mn2O4 correspon ds to a distinct step in the charging curve, suggestibly related to a Mn3(high-spin) to Mn4+ (low-spin) transition. The refined composition for the lambda-MnO2 phase at 4.3 V was Li0.28Mn2O4, and showed no evidence of lithi um/hydrogen ion-exchange. Electrochemical delithiation to form the lambda-M nO2 phase is concluded to involve a single spinel phase and not a coexisten ce of two-phases. (C) 1999 Elsevier Science B.V. All rights reserved.