Electrochemical cycling-induced spinel formation in high-charge-capacity orthorhombic LiMnO2

LixMn2O4 spinel normally undergoes a transformation from its cubic to tetra gonal phase when x exceeds 1 due to a collective Jahn-Teller distortion, re sulting in poor cyclability when both the 4 and 3 V intercalation plateaus are utilized. In this study, we show that this transformation is suppressed in spinels of composition up to x approximate to 2 obtained through the el ectrochemical cyclings of orthorhombic LiMnO2. X-ray diffraction, transmiss ion electron microscopy, and high-resolution electron microscopy studies to gether show that cycling produces a cubic spinel containing partial tetrahe dral cation site occupancy and a nanodomain structure (20 to 50 nm size) wi thin parent single-crystalline oxide particles. This structure is responsib le for the cycling stability of electrochemically produced spinel. The reve rsible capacity (272 mAh/g) and energy density (853 Wh/kg) achieved at a lo w charge-discharge rate (3;33 mA/g) in the present samples are the highest among crystalline LiMnO2 materials reported to dare. (C) 1999 The Electroch emical Society. S0013-4651 (99)01-103-9. All rights reserved.