Lithium–manganese spinel is prepared by a hydrothermal process that uses ethanol as the co-solvent. The crystallinity, particle morphology and electrochemical performance of the spinel are examined and compared with those obtained without the co-solvent. The amount of co-solvent and reaction time are adjusted to control the properties. The addition of ethanol leads to uniform particle size and shape, as well as higher crystallinity, than for spinel prepared in pure water. The co-solvent also reduces the time required for synthesis. A prolonged reaction time is effective in obtaining high-purity Li–Mn spinel in pure water but more impurities form after a long reaction time in an ethanol-added solvent. A mechanism for this process is suggested. A report is given of the electrochemical performance of Li–Mn spinel, including the capacity, rate capability and cyclability, as well as the effects of the co-solvent on these properties.