Evidence of structural fatigue has been detected at the surface of discharged Li-x[Mn-2]O-4 spinel electrodes in Li/Li-x[Mn-2]O-4 cells. Transmission electron microscopy has revealed a degradation of the structural integrity of Li[Mn-2]O-4 crystals in electrodes that were cycled between 3.3 and 2.2 V, where the transformation from cubic Li-2[Mn-2]O-4 to tetragonal Li-2[Mn-2]O-4 is expected. It has also been observed in cells cycled at voltages above the 3 V plateau that domains of tetragonal Li-2[Mn-2]O-4 coexist with cubic Li[Mn-2]O-4, even at 500 mV above the thermodynamic voltage expected for the onset of the tetragonal phase. It is proposed that the presence of Li-2[Mn-2]O-4 on the particle surface may contribute to some of the capacity fade observed during cycling of Li/Li-x[Mn-2]O-4 cells.