Electrochemical Cycling‐Induced Spinel Formation in High‐Charge‐Capacity Orthorhombic LiMnO2

spinel normally undergoes a transformation from its cubic to tetragonal phase when x exceeds 1 due to a collective Jahn‐Teller distortion, resulting 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 ≈ 2 obtained through the electrochemical cycling of orthorhombic . X‐ray diffraction, transmission electron microscopy, and high‐resolution electron microscopy studies together show that cycling produces a cubic spinel containing partial tetrahedral cation site occupancy and a nanodomain structure (20 to 50 nm size) within parent single‐crystalline oxide particles. This structure is responsible for the cycling stability of electrochemically produced spinel. The reversible capacity (272 mAh/g) and energy density (853 Wh/kg) achieved at a low charge‐discharge rate (3.33 mA/g) in the present samples are the highest among crystalline materials reported to date. © 1999 The Electrochemical Society. All rights reserved.