Emulsion-derived lithium manganese oxide powder for positive electrodes inlithium-ion batteries

Lithium manganese oxide (LiMn2O4) used as a positive-electrode material in lithium-ion batteries is prepared by a new water-in-oil emulsion process. A n aqueous solution containing lithium and manganese cations is emulsified i n kerosene by adding sorbitan monooleate as the surfactant. When the precur sor solution is agitated by a magnetic mixer, impure products are obtained. LiMn2O4 is formed along with residual Mn2O3 at elevated temperatures becau se of insufficient dispersion and mixing of the reactive cations. When a ho mogenizer with a greater agitation speed is used, however, a well-mixed pre cursor solution is prepared, and pure LiMn2O4 with a Fd 3 m structure is sy nthesized after calcination at 800 degreesC for 1 h. LiMn2O4 powder prepare d by the homogenizer has higher crystallinity, smaller particle size, and n arrower size distribution than that prepared by the magnetic stirrer. Compa red with powder prepared by the solid-state method, the LiMn2O4 powder exhi bits smaller particle size and less agglomeration. Moreover, the emulsion p rocess significantly shortens the heating time required. The prepared LiMn2 O4 powder has a high discharge capacity (120.4 mA h g(-1)) on the first cyc le and good cycleability. (C) 2001 Elsevier Science B.V. All rights reserve d.