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

Abstract

Lithium manganese oxide (LiMn 2O 4) used as a positive-electrode material in lithium-ion batteries is prepared by a new water-in-oil emulsion process. An aqueous solution containing lithium and manganese cations is emulsified in kerosene by adding sorbitan monooleate as the surfactant. When the precursor solution is agitated by a magnetic mixer, impure products are obtained. LiMn 2O 4 is formed along with residual Mn 2O 3 at elevated temperatures because of insufficient dispersion and mixing of the reactive cations. When a homogenizer with a greater agitation speed is used, however, a well-mixed precursor solution is prepared, and pure LiMn 2O 4 with a Fd 3 m structure is synthesized after calcination at 800°C for 1 h. LiMn 2O 4 powder prepared by the homogenizer has higher crystallinity, smaller particle size, and narrower size distribution than that prepared by the magnetic stirrer. Compared with powder prepared by the solid-state method, the LiMn 2O 4 powder exhibits smaller particle size and less agglomeration. Moreover, the emulsion process significantly shortens the heating time required. The prepared LiMn 2O 4 powder has a high discharge capacity (120.4 mA h g −1) on the first cycle and good cycleability.