Electrochemical lithium-ion extraction/insertion properties of Li1-xNiO2 single particles were investigated by attaching a filament microelectrode to the particle in 1 mol/dm(3) LiClO4/ethylene carbonate + propylene carbonate electrolyte. High-resolution cyclic voltammograms and galvanostatic chronopotentiograms were recorded. In addition, we observed in situ particle fracture during charge-discharge using an optical microscope equipped with a charge-coupled device camera. We found that the particle fractures when it is polarized above 4.2 V vs. Li/Li+. This phenomenon was explained by the change in crystal parameters expected to occur for x > 0.75 in Li1-xNiO2.